Patent Grant
8052249
The present invention relates to electrostatic actuators and, more particularly, to an electrostatic actuator used for a liquid-discharging mechanism such as an inkjet head of an inkjet recording apparatus.
An inkjet recording apparatus is used as an image recording apparatus or an image forming apparatus such as a printer, a facsimile machine, a copy machine, etc. An inkjet recording apparatus is equipped with an inkjet head as a droplet-discharging head. Generally, such an inkjet head comprises: a single or a plurality of nozzles for discharging droplets of ink; a discharge chamber connecting with the nozzles; and pressure generating means fox generating a pressure to pressurize the ink in the discharge chamber, the discharge chamber may be referred to as a pressurizing chamber, an ink chamber, a liquid chamber, a pressurizing liquid chamber, a pressure chamber or an ink passage. Droplets of ink are discharged from the nozzles by pressurizing the ink in the discharge chamber using a pressure generated by the pressure generating means.
Generally, a piezoelectric type, a thermal type and an electrostatic type are used for the inkjet head as a droplet discharge head. The piezoelectric inkjet head discharges droplets of ink by deforming a vibration plate (a diaphragm) that forms a wall of the discharge chamber by using an electromechanical transducer such as a piezoelectric element as the pressure generating means. The thermal inkjet head discharges droplets of ink by film boiling using an electrothermal transducer such as a heat-generating resistor provided in the discharge chamber. The electrostatic inkjet head discharges droplets of ink by deforming a vibration plate that forms a wall of the discharge chamber by an electrostatic force.
In recent years, the thermal type and the electrostatic type, which do not use parts containing lead, have attracted attention from the viewpoint of environmental issues. Especially, several electrostatic inkjet heeds have been suggested from the viewpoint of low power consumption in addition to the lead-free feature.
Japanese Laid-Open Patent Application No. 6-71882discloses an electrostatic inkjet head provided with a pair of electrodes with an air gap formed therebetween. One of the two electrodes serves as a vibration plate, and an ink chamber to be filled with ink is formed on a side of the vibration plate opposite to the electrode facing the vibration plate. An electrostatic attraction force is generated between the pair of electrodes by applying a voltage across the electrodes (between the vibration plate and electrode), which results in deformation of the electrode (vibration plate). The vibration plate returns to the original position due to an elastic force when the voltage is canceled, and a droplet of ink is discharged due to the return force of the vibration plate.
Additionally, Japanese Laid-Open Patent Application No. 2001-18383 and WO99/34979 disclose a structure of an inkjet head in which a small air gap is formed between the vibration plate and the electrode by etching a sacrifice layer, and a liquid chamber substrate is joined thereon.
Further, Japanese Laid-Open Patent Application No. 11-314363 discloses an inkjet head which can be driven at a low voltage by forming a vibration plate of a cantilever beam or a straddle mounted beam with a gap into which ink can flow, and filling a high dielectric-constant ink in the gap.
Additionally, Japanese Laid-Open Patent Application No. 9-193375 discloses an inkjet head having a vibration plate and an electrode that are positioned nonparallel to each other.
Further, Japanese Laid-open Patent Application No. 2001-277505 discloses an inkjet head, which attempts a low-voltage drive by varying a thickness of a dielectric insulating layer formed on the electrode so as to generate a nonparallel electric field.
In the electrostatic inkjet head containing the electrostatic actuator equipped with the vibration plate and the electrode facing the vibration plate, it is necessary to make the air gap between the electrodes very small so as to achieve a low-voltage drive.
However, in the head disclosed in the above-mentioned Japanese Laid-open Patent Application No. 6-71882, since the air gap is formed by formation of a cavity by etching and bonding a vibration plate substrate by anode junction, it is very difficult to accurately form such a small air gap with little variation, which causes a problem that the yield rate is low.
Thus, in the head disclosed in the above-mentioned Japanese Laid-open Patent Application No. 2001-18383, although the air gap is formed with sufficient accuracy in accordance with a gap-forming method using etching of the sacrifice layer, there is a problem in that a reliability of the vibration plate is low since etching holes for etching the sacrifice layer are formed in the vibration plate. Additionally, since the approach of sealing the etching holes by an insulating layer after etching the sacrifice layer is used, the insulating layer for sealing the etching holes must be thick, thus, there is a problem in that the rigidity of the vibration plate increases and a drive voltage increases, which causes a fluctuation in the rigidity of the vibration plate. Further, there is unevenness in the surface of the actuator substrate due to the formation of the air gap, and high alignment accuracy is required when joining a liquid chamber substrate. Moreover, since the junction area is small, it tends to cause a work mistake such as destruction due to a contact at the time of joining etc., and there is also a problem that a reliability is decreased and the yield rate is decreased.
Moreover, in the head disclosed in the above-mentioned Japanese Laid-Open Patent Application, No. 11-314363, although the air gap is formed by etching the sacrifice layer, the vibration plate has a structure of a cantilever beam or a straddle mounted beam and the air gap is communicated with the liquid chamber. In this case, since there is no need of forming the etching holes for etching the sacrifice layer and ink is allowed to enter the air gap, it is possible to achieve a low-voltage drive by using a high dielectric-constant ink which reduces an effective air gap. However, a problem tends to occur that an ink component is subjected to condensation since a voltage is applied to the ink in the gap, and there is a problem in that a high-speed drive cannot be performed due to the conductance of the ink in the gap.
Moreover, the above-mentioned Japanese Laid-Open Patent Application No. 9-193375 and Japanese Laid-Open Patent Application No. 2001-277505 do not disclose any method of forming a nonparallel air gap or any specific method for varying the thickness of the dielectric insulating layer, and, thus, a problem that it is very difficult to form a small air gap with little variation is not solved.
In the electrostatic inkjet head, the dimensional accuracy of a distance between the vibration plate and the electrode greatly affects the performance of the electrostatic inkjet head. Especially, in the case of an inkjet head, if the variation in the characteristic of each actuator is large, accuracy in printing and reproducibility of image quality goes down remarkably. Moreover, in order to attain a low-voltage operation, the size of the air gap must be 0.2 μm to 2.0 μm, which requires higher dimensional accuracy.
Japanese Laid-Open Patent Application No. 2001-18383 and WO99/34979 disclose a head constituted by forming a small air gap between the vibration plate and the electrode by applying a sacrifice layer process (etching the sacrifice layer) and joining a flow passage substrate thereon. According to this approach, the size o the air gap is determined by variation in a process of forming the sacrifice layer, and, thus, variation in the size can be suppressed, thereby obtaining an actuator or a head having high accuracy and high reliability.
Moreover, when the air gap is formed using the sacrifice layer process as mentioned above, it is necessary to seal the through holes for removing the sacrifice layer (sacrifice layer removal holes). Thus, WO99/34979 disclose that the sacrifice layer removal holes are closed by a Ni film or SiO2 film formed by a PVD or CVD method after the sacrifice layer is removed. However, if the sacrifice layer removal holes are sealed by such a film deposition method, the components of the film may enter the air gap. Additionally, the sacrifice layer removal holes also serve to maintain a strength of the partition wall, and they cannot be made small. Therefore, the sacrifice layer removal holes being sealed by the film deposition using a PVD or CVD method may influence the operation characteristic and reliability of the actuator and it cannot deal with densification.
Moreover, in the head disclosed in Japanese Laid-Open Patent Application No. 2001-18383, there is formed a step in the partition parts and the vibration plate, which requires high accuracy in joining the flow passage substrate. Moreover, since the thin vibration plate is floated on the surrounding parts after the sacrifice layer is removed, the vibration plate may be damaged in the subsequent process and it is difficult to manufacture the actuator with a sufficient yield rate.
Additionally, although the sacrifice layer removal holes are sealed by a film formed by a film deposition method using a vacuum device, the use of the vacuum device may cause a problem. If the film deposition is performed by the vacuum device, the film deposition process is performed in a vacuum environment and the air gap between the vibration plate and the electrode is sealed in vacuum. Therefore, there is a problem in that the vibration plate may be bent due to a negative pressure inside the air gap when the actuator is exposed to an atmosphere. Additionally, if there is variation in the bent of the vibration plate, there may occur variation in the displacement of the vibration plate. In addition, since the vacuum seal cannot provide a damping effect of a gas sealed in the air gap, variation in amplitude of vibration with respect to variation in the thickness of the vibration plate becomes large.
In order to solve such a problem, it is necessary to provide a structure or a process for opening the air to the atmosphere, which causes an increase in the cost and deterioration in the yield rate. Thus, if the conventional sacrifice layer process is used, it is difficult to obtain an electrostatic actuator having high-accuracy and reliability at a low cost.
In the meantime, in an inkjet recording apparatus, in order to achieve high-definition recording of a color image at high speed, high-density processing using a micro-machining technology is used to obtain a high-quality image. Thus, materials of parts constituting the head are shifted from metal or plastic to silicon, glass or ceramics. Especially, silicon is used as a material, which is suitable for the micro-processing.
Moreover, in respect of colorization, developments of ink and recording media are a main streams, and developments have been progressed with respect to components and compositions of ink so as to optimize absorbability, coloring characteristic and color-mixture prevention characteristic or improve a long-term storage of printed media and storage stability of ink itself.
In such a case, depending on a combination of ink and a material of component parts of the head, the component parts may be dissolved in the ink. Especially, if a flow passage formation member is formed of silicon, silicon is eluted in ink and is deposited on a nozzle part, which causes degradation of image quality due to nozzle clogging or deterioration of coloring of ink. Moreover, in the head using a vibration plate formed of a thin silicon film, if the silicon forming the vibration plate is eluted in ink, the vibration characteristic may be changed or the vibration plate cannot vibrates.
If the material of the component parts is changed to solve the problem, it is difficult to realize high-density processing or processing accuracy may be deteriorated in many cases. Moreover, the change in the material requires a large change in the fabrication process or assembly process, which results in decrease of nozzle density and consequently causing degradation of the print quality.
On the other hand, if the problem is solved by adjustment of components of ink, a high-quality image may be deteriorated since the components and composition of ink are originally adjusted so that permeability and coloring characteristics with respect to recording medium are optimized so as to improve the printing quality and storage stability is improved.
Thus, in the conventional inkjet head, a thin film having an ink resistance is formed on a surface of a flow passage forming member that is brought into contact with ink. For example, forming titanium, titanium compound, or aluminum oxide on the surface which contacts with ink is disclosed in WO98/42513. Forming an oxide film on the surface which contact with ink is disclosed in Japanese Laid-Open Patent Application No. 5-229118. Forming a thin film such as oxide, nitride or metal having an ink resistance on a surface of a silicon oxide film is disclosed in Japanese Laid-Open Patent Application No. 10-291322. Forming an organic resin film on a surface of the ink chamber formed of a piezoelectric material is disclosed in Japanese Laid-Open Patent Application No. 2000-246895.
In the above-mentioned head, an organic resin film such as paraxylene may be formed as a corrosion resistant film on sidewalls of an ink chamber having a complex three-dimensional configuration and the vibration plate. Since the organic resin film such as paraxylene is formed by the vacuum vapor deposition method, the covering characteristic of the film is not good due to its nature of deposition, and a large unevenness arises in the distribution of film thickness inside the liquid chamber or on the vibration plate.
When an area where the film thickness is small contacts with ink for a long time, there is a large problem arises in the long-time reliability since the corrosion resistant film is dissolved and finally the base material is subjected to corrosion. Moreover, a large bend is generated due to a distribution of internal stresses caused by variation of film thickness of the organic resin film on the vibration plate, which causes a large variation in the ink injection characteristic.
Moreover, in the head in which a metallic ink resistant film is formed on the vibration plate by a sputtering method or a vapor deposition method, the covering characteristic of the corrosion resistant film is poor similar to the above-mentioned organic resin film. Depending on the location, an area in which the corrosion resistant film is formed with a very small thickness, and when ink contacts such an area for long time, the corrosion resistant film is dissolved and finally the base material is subjected to corrosion. Therefore, a long-time reliability cannot be obtained, and further a large bent is generated in the vibration plate due to fluctuation in the thickness of the metallic ink-resistant film, which causes variation in the ink injection characteristic.
Especially, this problem is serious in the electrostatic head rather than the piezoelectric head since the distance between the vibration plate and the electrode varies due to the vibration plate being bent and the drive voltage differing from the design value.
Further, in the head in which the above-mentioned corrosion resistant film is formed, the reliability of operation is low such that the vibration plate contacts the electrode due to an influence of an external environment such as humidity since the air gap between the vibration plate and the electrode is not sealed.
Moreover, in the head in which the air gap between the vibration plate and the electrode is sealed so as not to receive an influence from an external environment, there is a restriction of pH value of ink that is usable since the corrosion resistant film is not formed on the vibration plate, and, thus, matching with ink roust be maintained and a cost is increased.
In an aspect of this disclosure, there is provided an electrostatic actuator having less variation in characteristics and having a high-reliability and various apparatuses using such an electrostatic actuator.
In another aspect, there is provided an electrostatic actuator which can be driven at a low voltage and various apparatuses using such an electrostatic actuator.
In another aspect, there is provided an electrostatic actuator and apparatuses using such an electrostatic actuator which can provide a stable liquid discharge characteristic and a sufficient long-time reliability by preventing component parts from being corroded and preventing an influence of an external environment.
Further, there is provided, according to another aspect, an electrostatic actuator comprising: a substrate; an electrode formed on the substrate; a plurality of partition parts formed on the electrode; a vibration plate formed on the partition parts, the vibration plate being deformable by an electrostatic force generated by a voltage applied to the electrode; and an air gap formed between the plurality of partition parts by etching a part of a sacrifice layer formed between the electrode and the vibration plate, wherein the partition parts comprise remaining parts of the sacrifice layer after the etching.
In the aforementioned electrostatic actuator, since the air gap between the vibration plate and the electrode is formed by etching the sacrifice layer, the distance between the vibration layer and the electrode can be accurately set to the thickness of the sacrifice layer. Additionally, the partition parts defining the air gap between the vibration plate and the electrode are formed by the remaining parts of the sacrifice layer after forming the air gap by etching, an upper surface of the vibration plate can be made flat. The aforementioned electrostatic actuator formed by a semiconductor manufacturing process has a stable performance with less variation in characteristics.
In the aforementioned electrostatic actuator, the substrate is preferably a silicon substrate.
The aforementioned electrostatic actuator may further comprise dummy electrodes at positions corresponding to the partition parts, the dummy electrodes being electrically separated from the electrode by separation grooves.
In the aforementioned electrostatic actuator, the sacrifice layer is preferably formed of a material selected from a group consisting of polysilicon, amorphous silicon, silicon oxide, aluminum, titanium nitride and polymer. Additionally, the electrode is preferably formed of a material selected from a group consisting of polysilicon, aluminum, titanium, titanium nitride, titanium silicide, tungsten, tungsten silicide, molybdenum, molybdenum silicide and ITO.
In the aforementioned electrostatic actuator, an insulating layer may be formed on the electrode, and the separation grooves are filled with the insulating layer. A thickness of the insulating layer preferably equal to or greater than one half of a width of each of the separation grooves.
In the aforementioned electrostatic actuator, the sacrifice layer may be divided by separation grooves, and an insulating layer may be formed on the sacrifice layer so that the separation grooves are filled with the insulating layer. A thickness of the insulating layer preferably is equal to or greater than one half of a width of each of the separation grooves.
In the aforementioned electrostatic actuator, the sacrifice layer is preferably formed of a conductive material, and the remaining parts of the sacrifice layer may be electrically connected to one of the substrate, the electrode and the vibration plate so that the remaining parts are at the same potential with the one of the substrate, the electrode and the vibration plate. Additionally, the sacrifice layer is preferably formed of a conductive material, and at least one of the remaining parts of the sacrifice layer and the dummy electrodes may serve as a part of electric wiring.
The aforementioned electrostatic actuator may further comprise insulating layers on the electrode and a surface of the vibration plate facing the electrode, wherein the sacrificing layer may be formed of one of polysilicon and amorphous silicon, and the insulating layers may be formed of silicon oxide.
In the aforementioned electrostatic, the sacrificing layer is formed of silicon oxide and the electrode may be formed of polysilicon.
In the aforementioned electrostatic actuator, a through hole may be formed in the vibration plate for removing by etching the parts of the sacrifice layer through the through hole so as to form the air gap.
In the aforementioned electrostatic actuator, the through hole may be located near the partition parts. The vibration plate may have substantially a rectangular shape, and a shorter side of the vibration plate may be substantially equal to or less than 150 μm. A distance of the air gap measured in a direction perpendicular to a surface of the electrode facing the vibration plate may be substantially 0.2 μm to 2.0 μm.
Additionally, in the aforementioned electrostatic actuator, a plurality of the through holes may be arranged along a longer side of the vibration plate at an interval equal to or less than a length of the shorter side of the vibration plate.
The aforementioned electrostatic actuator may further comprise: a through hole formed in the vibration plate for removing the parts of the sacrifice layer through the through hole so as to form the air gap; and a resin film formed on a surface opposite to a surface facing the electrode, wherein the through hole are sealed by a joining surface of the resin film. A cross-sectional area of each of the through holes may be substantially equal to or greater than 0.19 μm2 and equal to or less than 10 μm2. A thickness of an insulator layer in a periphery of an opening of the through hole may be substantially equal to or greater than 0.1 μm. The air gap between the electrode and the vibration plate may be substantially equal to or greater than 0.1 μm. The resin film may have a corrosion resistance with respect to a substance to be brought into contact with the vibration plate. The resin film may be formed of one of a polybenzaoxazole film and a polyimide film.
The aforementioned electrostatic actuator may further comprise a member joined to an upper surface of the vibration plate, wherein the through holes are sealed by a joining surface of the member.
The aforementioned electrostatic actuator may further comprise an insulating layer formed on a surface of the vibration plate facing the electrode, wherein a thickness of the insulating layer near a center between the partition parts adjacent to each other is larger than a thickness of the insulating layer near the partition parts.
The aforementioned electrostatic actuator may further comprise an insulating layer formed on the electrode, wherein a thickness of the insulating layer near a center between the partition parts adjacent to each other is larger than a thickness of the insulating layer near the partition parts.
In the aforementioned electrostatic actuator, a cavity may be formed between the electrode and the substrate, and the electrode may have a connection through hole connecting the cavity to the air gap.
The aforementioned electrostatic actuator may further comprise insulating layers on both sides of the electrode, wherein a total thickness of the electrode and the insulating layers exceeds a thickness of the vibration plate.
Additionally, there is provided, according to another aspect of this disclosure, a method for manufacturing an electrostatic actuator comprising the steps of: forming an electrode on a substrate; forming a sacrifice layer on the electrode; forming a vibration plate on the sacrifice layer, the vibration plated being deformable by an electrostatic force generated by a voltage applied to the electrode; and forming an air gap between the electrode and the vibration plate by removing a part of the sacrifice layer by etching so that remaining parts of the sacrifice layer after the etching form partition parts that define the air gap.
According to the aforementioned method, since the air gap between the vibration plate and the electrode is formed by etching the sacrifice layer, the distance between the vibration layer and the electrode can be accurately set to the thickness of the sacrifice layer. Additionally, the partition parts defining the air gap between the vibration plate and the electrode are formed by the remaining parts of the sacrifice layer after forming the air gap by etching, an upper surface of the vibration plate can be made flat. Thus, the electrostatic actuator is formed by a semiconductor manufacturing process, which results in a stable performance with less variation in characteristics.
In the aforementioned method, the air gap forming step preferably includes etching the part of the sacrifice layer after forming the electrode and the vibration plate.
Additionally, the aforementioned method may further comprise a step of forming an insulating layer on the electrode before forming the sacrificing layer, wherein the air gap forming step includes etching the insulating layer so that a thickness of the insulating layer near a center between the partition parts adjacent to each other is larger than a thickness of the insulating layer near the partition parts.
The aforementioned method may further comprise a step of forming an insulating layer on a surface of the vibration plate facing the electrode after forming the sacrificing layer, wherein the air gap forming step includes etching the insulating layer so that a thickness of the insulating layer near a center between the partition parts adjacent to each other is larger than a thickness of the insulating layer near the partition parts.
The aforementioned method may further comprise: a step of forming an insulating layer on the electrode; and a step of forming an insulating layer on a surface of the vibration plate facing the electrode, wherein the etching of the sacrifice layer is performed by one of a plasma-etching method using sulfur hexafluoride (SF6) or xenon difluoride (XeF2) and a wet-etching method using tetra-methyl-ammonium-hydroxide (TMAH).
The aforementioned method for manufacturing an electrostatic actuator may further comprise the steps of: forming a through hole in the vibration plate for removing the part of the sacrifice layer; and forming a resin film on the vibration plate so as to seal the through hole.
In the aforementioned method for manufacturing an electrostatic actuator, the vibration plate forming step may include a step of forming the vibration plate in a rectangular shape having a shorter side substantially equal to or smaller than 150 μm. The vibration plate forming step may include a step of forming a bend-preventing film that prevents the vibration plate from being bent. Additionally, the resin film forming step may include a step of changing a surface condition of the vibration plate by exposing a surface of the vibration plate, on which the resin film is formed, to a fluorine compound gas including sulfur hexafluoride (SF6) and xenon difluoride (XeF2). Further, the resin film forming step may include a step of changing a surface condition of the vibration plate by exposing to plasma a surface of the vibration plate on which the resin film is formed. The resin film forming step may include forming the resin film by a material having a corrosion resistance with respect to a liquid to be brought into contact with the vibration plate. The resin film forming step may include forming the resin film by a spin-coating method.
The aforementioned method for manufacturing an electrostatic actuator may further comprise the steps of: forming a plurality of through holes in the vibration plate for removing the part of the sacrifice layer; and joining a sealing member to the surface of the vibration plate so as to seal the through holes.
Additionally, there is provided according to another aspect of this disclosure a droplet discharging head comprising: a nozzle for discharging a droplet of a liquid; a liquid pressurizing chamber connecting with the nozzle and storing the liquid; and an electrostatic actuator for pressurizing the liquid stored in the liquid pressurizing chamber, wherein the electrostatic actuator comprises: a substrate; an electrode formed on the substrate; a plurality of partition parts formed on the electrode; a vibration plate formed on the partition parts, the vibration plate being deformable by an electrostatic force generated by a voltage applied to the electrode; and an air gap formed between the plurality of partition parts by etching a part of a sacrifice layer formed between the electrode and the vibration plate, wherein the partition parts comprise remaining parts of the sacrifice layer after the etching.
In the aforementioned droplet discharging head, a plurality of through holes may be formed in the vibration plate for removing by etching the parts of the sacrifice layer through the through holes so as to form the air gap, and a flow passage forming member forming the liquid pressurizing chamber may seal the through holes of the vibration plate. The through holes may be formed near the partition parts.
Further, there is provided according to another aspect of this disclosure a liquid supply cartridge comprising: a droplet discharging head for discharging droplets of a liquid; and a liquid tank integrated with the droplet discharging head for supplying the liquid to the droplet discharging head, wherein the droplet discharging head comprises: a nozzle for discharging the droplets of the liquid; a liquid pressurizing chamber connecting with the nozzle and storing the liquid; and an electrostatic actuator for pressurizing the liquid stored in the liquid pressurizing chamber, wherein the electrostatic actuator comprises: a substrate; an electrode formed on the substrate; a plurality of partition parts formed on the electrode; a vibration plate formed on the partition parts, the vibration plate being deformable by an electrostatic force generated by a voltage applied to the electrode; and an air gap formed between the plurality of partition parts by etching a part of a sacrifice layer formed between the electrode and the vibration plate, wherein the partition parts comprise remaining parts of the sacrifice layer after the etching.
Additionally, there is provided according to another aspect of this disclosure an inkjet recording apparatus comprising: an inkjet head for discharging droplets of ink; and an ink tank integrated with the inkjet head for supplying the ink to the inkjet head, wherein the inkjet head comprises: a nozzle for discharging droplets of the ink; a liquid pressurizing chamber connecting with the nozzle and storing the ink; and an electrostatic actuator for pressurizing the ink stored in the liquid pressurizing chamber, wherein the electrostatic actuator comprises: a substrate; an electrode formed on the substrate; a plurality of partition parts formed on the electrode; a vibration plate formed on the partition parts, the vibration plate being deformable by an electrostatic force generated by a voltage applied to the electrode; and an air gap formed between the plurality of partition parts by etching a part of a sacrifice layer formed between the electrode and the vibration plate, wherein the partition parts comprise remaining parts of the sacrifice layer after the etching.
Additionally, there is provided according to another aspect of this disclosure a liquid jet apparatus comprising: a droplet discharge head for discharging droplets of a liquid; and a liquid tank integrated with the droplet discharging head for supplying the liquid to the droplet discharging head, wherein the droplet discharging head comprises: a nozzle for discharging the droplets of the liquid; a liquid pressurizing chamber connecting with the nozzle and storing the liquid; and an electrostatic actuator for pressurizing the liquid stored in the liquid pressurizing chamber, wherein the electrostatic actuator comprises: a substrate; an electrode formed on the substrate; a plurality of partition parts formed on the electrode; a vibration plate formed on the partition parts, the vibration plate being deformable by an electrostatic force generated by a voltage applied to the electrode; and an air gap formed between the plurality of partition parts by etching a part of a sacrifice layer formed between the electrode and the vibration plate, wherein the partition parts comprise remaining parts of the sacrifice layer after the etching.
Additionally, there is provided according to another aspect of this disclosure a micro pump comprising: a flow passage through which a liquid flows: an electrostatic actuator for deforming the flow passage so that the liquid flows in the flow passage, wherein the electrostatic actuator comprises: a substrate; an electrode formed on the substrate; a plurality of partition parts formed on the electrode; a vibration plate formed on the partition parts, the vibration plate being deformable by an electrostatic force generated by a voltage applied to the electrode; and an air gap formed between the plurality of partition parts by etching a part of a sacrifice layer formed between the electrode and the vibration plate, wherein the partition parts comprise remaining parts of the sacrifice layer after the etching.
Additionally, there is provided according to another aspect of this disclosure an optical device comprising: a mirror reflecting a light; and an electrostatic actuator for deforming the mirror, wherein the electrostatic actuator comprises: a substrate; an electrode formed on the substrate; a plurality of partition parts formed on the electrode; a vibration plate formed on the partition parts, the vibration plate being deformable by an electrostatic force generated by a voltage applied to the electrode; and an air gap formed between the plurality of partition parts by etching a part of a sacrifice layer formed between the electrode and the vibration plate, wherein the partition parts comprise remaining parts of the sacrifice layer after the etching, and the mirror is formed on the vibration plate so that the mirror is deformable by deformation of the vibration plate.
The aforementioned and other aspects, features and advantages will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.
A description will now be given, with reference to
In the figures, 1 denotes a substrate which forms an actuator; 11 an insulating layer; 12a an electrode (may be referred to as individual electrode); 14 a sacrifice layer; 15 an insulating layer (may be referred to as a vibration plate side insulating layer); 16 a vibration plate electrode layer; and 17 an insulating layer which also serves as a stress-adjustment of a vibration plate. Additionally, 19 denotes a vibration plate constituted by the insulating layer 15, the vibration plate electrode layer 16 and the insulating layer 17. Further, 14a denotes an air gap formed by removing a part of the sacrifice layer; “g” a distance of the air gap; 60 a sacrifice layer removing hole (through hole); 50a a partition part; 14b a remaining sacrifice layer which remains in the partition part 50a; and 10 an actuator forming part in which the actuator is formed.
The actuator forming part 10 of the first embodiment comprises: the substrate 1 which forms the actuator; the electrodes 12a formed on the substrate 1; the partition parts 50a formed on the electrodes 12a; the vibration plate 13 which is formed on the partition parts 50a and is deformable by an electrostatic force generated by a voltage applied to the electrodes 12a; and the air gap 14a formed between adjacent partition parts 50a. The air gap 14a is formed by removing by etching parts of the sacrifice layer 14 formed between the electrodes 12a and the electrodes 16 of the vibration plate 19. It is noted that other parts of the sacrifice layer 14, which are not removed by etching, remain in the partition parts 50a.
The actuator forming member 10 is formed by repeating a film deposition and film processing (photo-lithography and etching) so as to form electrodes and insulation layers on a substrate having a high degree of cleanness. A high-temperature process may be used to form the actuator forming member 10 by using silicon to make the substrate 1. It should be noted that the high-temperature process refers to a process for forming a high-quality film such as a thermal oxidizing method or a thermal nitriding method, a thermal CVD method which forms a high-temperature oxide film (HTO) or an LP-CVD method which forms a good-quality nitride film. By adopting the high-temperature process, high-quality electrode materials and insulating materials become usable, which can provide an actuator device having excellent conductivity and insulation. Moreover, the high-temperature process is excellent in controllability and reproducibility of a film thickness, thereby providing an actuator device having little variation in the electric properties. Further, since the controllability and reproducibility are excellent, process design becomes easy and a mass production at low cost can be achieved.
In
Important factors to fill the insulating layer in the separation groove are a film deposition method, which can form a conformal insulating layer, and a relationship between the width of the separation groove and the thickness of the insulating layer.
Here, as a material of the electrode layer 12 for forming the electrodes 12a, a compound silicide such as polysilicon, titanium silicide, tungsten silicide or molybdenum silicide or a metal compound such as titanium nitride may be preferably used. Since these materials can be deposited and processed with a stable quality and can be made into a structure which withstands a high-temperature process, there is less restriction with respect to temperatures in other processes. For example, a HTO (High-Temperature-Oxide) film or the like can be laminated on the electrode layer 12 as the insulating layer 13, the HTO film being an insulating layer having high reliability. Thus, the selection range can be enlarged, and cost reduction and improvement of reliability can be attempted. Additionally, a material such as aluminum, titanium, tungsten, molybdenum or ITO can also be used. By using these materials, a remarkable resistance reduction can be attempted, which results in reduction in a drive voltage. Additionally, since deposition and processing of films made of these materials can be easily achieved with a stable quality, cost reduction and improvement of reliability can be attempted.
In
Here, as a material of the sacrifice layer 14, it is preferable to use polysilicon or amorphous silicon. These materials can be very easily removed by etching, and it is preferable to use an isotropic dry etching method using SF6 gas, a dray etching method using XeF2 gas or a wet etching method using a solution of tetra methyl ammonium hydroxide (TMAH). Additionally, since polysilicon and amorphous silicon are generally-used, inexpensive materials and withstand a high temperature, a degree of freedom of a process in a subsequent process is also high. Further, since variation in the distance “g” of the air gap 14a, which is very important, can be extremely small by arranging silicon oxide films (insulating layers 13 and 15) having a high etching resistance above and below the sacrifice layer, an accurate actuator having little variation in properties can be obtained. Moreover, mass production is also easy at low cost.
As for a material of the sacrifice layer 14, titanium nitride, aluminum, silicone oxide or polymer material such as a resin film may be used. Additionally, from among resin films, a photosensitive resin material (a resist material) is preferably used since such a material can be easily processed. Although an etchant (etching material) and the air gap forming process depend on the material forming the sacrifice 14 and process difficulty and process cost thereof may also vary depending on the material of the sacrifice layer 14, the material of the sacrifice layer 14 can be selected based on its purpose.
When a silicone oxide film is used for the sacrifice layer 14, it is preferable to use polysilicon as a protective film (etching stopper) of the etching of the sacrifice layer. The polysilicon film may be commonly used for the electrode layer 12 and the vibration plate electrode layer. In order to remove the oxide film forming the sacrifice layer 14, it is preferable to use a wet etching method, a HF vapor method, a chemical dry etching method, etc. If an insulating layer is needed inside the air gap 14a, the insulating layer may be formed by oxidizing a surface of the polysilicon film remaining as an etching stopper. Thus, if a silicon oxide film is used as the sacrifice layer 14, the removal of the sacrifice layer 14 can be performed by using etching materials used in semiconductor manufacturing processes. Additionally, if polysilicon films are formed on both sides of the sacrifice layer 14, a manufacturing process with little variation can be achieved. Further, the polysilicon film can be uses as an electrode as it is, which enables mass production at a low cost. Moreover, the thus-obtained actuator also provides high quality and accuracy.
Moreover, similar process can be achieved by various combinations of the material of the sacrifice layer 14 and the etchant. For example, the sacrifice layer 14 may be removed by O2 plasma or an exfoliation liquid when a polymer material is used for the sacrifice layer 14. The sacrifice layer 14 may be removed by a liquid such as KOH when aluminum is used for the sacrifice layer 14. The sacrifice layer 14 may be removed by chemicals such as a mixture solution of NH2OH and H2O2 when titanium nitride is used for the sacrifice layer 14.
In
Additionally, similar to the case of filling the insulating layer 13 in the separation grooves 82 of the electrode layer 12, it is preferable to form the insulating layer 15 with a thickness equal to or less than ½ of the width of the separation grooves 84 of the sacrifice layer 14 in the case where the insulating layer 15 is filled in the separation grooves 84 of the sacrifice layer 14. However, it is also possible to fill an entire vibration plate layer (lamination of the insulating layer 15, the vibration plate electrode layer 16 and the insulating layer 17) in the separation grooves 84. Therefore, normally, the width of the separation grooves 84 of the sacrifice layer 14 can be larger than the width of the separation grooves 82 of the electrode layer 12. As mentioned above, a level difference (step or unevenness) of the surface of the actuator forming member can be almost eliminated, and the effect of such is the same as that explained before.
As a material of the vibration plate electrode layer 16 which constitutes a part of the vibration plate 19, materials such as polysilicon, titanium silicide, tungsten silicide, molybdenum silicide, titanium nitride, aluminum, titanium, tungsten, molybdenum may be used for the same reason as the material of the electrode layer 12. Additionally, a transparent film such as an ITO film, a nesa film or a ZnO film can also be used. When the transparent film is used, the inspection inside the air gap 14a can be easily performed. Thus, an abnormality can be detected during a manufacturing process, which contributes to an attempt of cost reduction and improvement of reliability.
As mentioned above, the surface of the actuator forming member 10 (the surface of the vibration plate 19) can be substantially flat due to filling of the insulating layer 13 in the separation grooves 82 of the electrode layer 12, filing of the insulating layer 15 in the separation grooves 84 of the sacrifice layer 14, the sacrifice layer 14b being remained in the partition parts 50a, and etching of the sacrifice layer 14 through the sacrifice layer removing holes 60 formed in the vibration plate 19. Since the surface of the actuator is flattened, a resin film forming process can be performed, as mentioned later, for the purpose of acquiring an environment resistance (measures for high humidity) by sealing the sacrifice layer removing holes 60 and also acquiring a corrosion resistance of the vibration plate 19. Moreover, when it is necessary to join a separate member to the actuator device, such a joining process can be easily performed.
As mentioned above, the electrostatic actuator according to the present embodiment has little variation in properties and has high reliability. Additionally, the electrostatic actuator according to the present embodiment can be manufactured by mass production at a low cost.
A description will now be given, with reference to
In the figures, 1 denotes a substrate which forms an actuator; 11 an insulating layer; 12a an electrode (may be referred to as individual electrode); 12b a dummy electrode; 14 a sacrifice layer; 15 an insulating layer (may be referred to as a vibration plate side insulating layer); 16 a vibration plate electrode layer; and 17 an insulating layer which also serves as a stress-adjustment of a vibration plate. Additionally, 19 denotes a vibration plate constituted by the insulating layer 15, the vibration plate electrode layer 16 and the insulating layer 17. Further, 14a denotes an air gap formed by removing a part of the sacrifice layer; “g” a distance of the air gap; 60 a sacrifice layer removing hole (through hole); 50a a partition part; 14b a remaining sacrifice layer which remains in the partition part 50a; and 10 an actuator forming part in which the actuator is formed.
The actuator forming part 10 of the second embodiment comprises: the substrate 1 which forms the actuator; the electrode layer 12 (electrodes 12a and dummy electrodes 12b) formed on the substrate 1; the partition parts 50a formed on the electrodes layer 12; the vibration plate 19 which is formed on the partition parts 50a and is deformable by an electrostatic force generated by a voltage applied to the electrodes 12a; and the air gap 14a formed between adjacent partition parts 50a. The air gap 14a is formed by removing by etching parts of the sacrifice layer 14 formed between the electrodes 12a and the electrodes 16 of the vibration plate 19. It is noted that other parts of the sacrifice layer 14, which are not removed by etching, remain in the partition parts 50a as a remaining sacrifice layer 14b.
The actuator forming member 10 is formed by repeating a film deposition and film processing (photo-lithography and etching) so as to form electrodes and insulation layers on a substrate having a high degree of cleanness. A high-temperature process may be used to form the actuator forming member by using silicon to make the substrate 1. It should be noted that the high-temperature process refers to a process for forming a high-quality film such as a thermal oxidizing method or a thermal nitriding method, a thermal CVD method which forms a high-temperature oxide film (HTO) or an LP-CVD method which forms a good-quality nitride film. By adopting the high-temperature process, high-quality electrode materials and insulating materials become usable, which can provide an actuator device having excellent conductivity and insulation. Moreover, the high-temperature process is excellent in controllability and reproducibility of a film thickness, thereby providing an actuator device having little variation in the electric properties. Further, since the controllability and reproducibility are excellent, process design becomes easy and a mass production at low cost can be achieved.
In
In order to completely fill the separation grooves 82 by the insulating layer 13, it is preferable to set a thickness of the insulating layer 13 substantially equal to or greater than ½ of a width of the separation groove so as to form the surface of the insulating layer substantially flat. Or, it is preferable to set the width of the separation groove equal to or smaller than twice the thickness of the insulating layer. According to the above-mentioned relationship, the separation groove can be completely filled by the insulating layer, which results in a substantially flat surface of the insulating layer. Thus, since a surface level difference can be mostly eliminated by forming the insulating layer with a thickness substantially equal to or greater than ½ of the width of the separation grooves 82 of the electrode layer 12, subsequent processes explained below, such as an air gap forming process, a resin film forming process or a joining process with other members, can be easily performed. As a result, an actuator having an air gap with an accurate distance thereof can be obtained, and, at the same time, it can be attempted to reduce a cost and improve reliability.
Here, as a material of the electrode layer 12 for forming the electrodes 12a, a compound silicide such as polysilicon, titanium silicide, tungsten silicide or molybdenum silicide or a metal compound such as titanium nitride may be preferably used. Since these materials can be deposited and processed with a stable quality and can be made into a structure which withstands a high-temperature process, there is less restriction with respect to temperatures in other processes. For example, a HTO (High-Temperature-Oxide) film or the like can be laminated on the electrode layer 12 as the insulating layer 13, the HTO film being an insulating layer having high reliability. Thus, the selection range can be enlarged, and cost reduction and improvement of reliability can be attempted. Additionally, a material such as aluminum, titanium, tungsten, molybdenum or I′TO can also be used. By using these materials, a remarkable resistance reduction can be attempted, which results in reduction in a drive voltage. Additionally, since deposition and processing of films made of these materials can be easily achieved with a stable quality, cost reduction and improvement of reliability can be attempted.
In
Here, as a material of the sacrifice layer 14, it is preferable to use polysilicon or amorphous silicon. These materials are most easily removable by etching, and it is preferable to use an isotropic dry etching method using SF6 gas, a dray etching method using XeF2 gas or a wet etching method using a solution of tetra methyl ammonium hydroxide (TMAH). Additionally, since polysilicon and amorphous silicon are generally-used, inexpensive materials and withstand a high temperature, a degree of freedom of a process in a subsequent process is also high. Further, since variation in the distance “g” of the air gap 14a, which is very important, can be extremely small by arranging silicon oxide films (insulating layers 13 and 15) having a high etching resistance above and below the sacrifice layer, an accurate actuator having little variation in properties can be obtained. Moreover, mass production is also easy at low cost.
As for a material of the sacrifice layer 14, titanium nitride, aluminum, silicone oxide or polymer material such as a resin film may be used. Additionally, from among resin films, a photosensitive resin material (a resist material) is preferably used since such a material can be easily processed. Although an etchant (etching material) and the air gap forming process depend on the material forming the sacrifice 14 and process difficulty and process cost thereof may also vary depending on the material of the sacrifice layer 14, the material of the sacrifice layer 14 can be selected based on its purpose.
When a silicone oxide film is used for the sacrifice layer 14, it is preferable to use polysilicon as a protective film (etching stopper) of the etching of the sacrifice layer. The polysilicon film may be commonly used for the electrode layer 12 and the vibration plate electrode layer. In order to remove the oxide film forming the sacrifice layer, it is preferable to use a wet etching method, a HF paper method, a chemical dry etching method, etc. If an insulating layer is needed inside the air gap 14a, the insulating layer may be formed by oxidizing the polysilicon film remaining as an etching stopper. Thus, if a silicon oxide film is used as the sacrifice layer 14, the removal of the sacrifice layer 14 can be performed by using etching materials used in semiconductor manufacturing processes. Additionally, if polysilicon films are formed on both sides of the sacrifice layer, a manufacturing process with little variation can be achieved. Further, the polysilicon film can be uses as an electrode as it is, which enables mass production at a low cost. Moreover, the thus-obtained actuator also provides high quality and accuracy.
Moreover, similar process can be achieved by various combinations of the material of the sacrifice layer and the etchant. For example, the sacrifice layer 14 may be removed by O2 plasma or an exfoliation liquid when a polymer material is used for the sacrifice layer 14. The sacrifice layer 14 may be removed by a liquid such as KOH when aluminum is used for the sacrifice layer 14. The sacrifice layer 14 may be removed by chemical such as a mixture solution of NH2OH and H2O2 when titanium nitride is used for the sacrifice layer 14.
In
In the example of
Moreover, the sacrifice layer 14b can remain in the partition parts due to existence of the insulating layer 15 filled in the separation grooves 64. The effect of small steps or unevenness is as mentioned above.
Moreover, since the filled insulating layer is securely fixed to the wall surfaces of the sacrifice layer 14b, which results in the vibration plate 19 being firmly fixed by the partition parts 50a, an accuracy of the distance “g” of the air gap 14b of the thus-obtained actuator is high and also excellent in structural durability.
Additionally, similar to the case of filling the insulating layer 13 in the separation grooves 32 of the electrode layer 12, it is preferable to form the insulating layer 15 with a thickness equal to or less than ½ of the width of the separation groove of the sacrifice layer 14 in the case where the insulating layer 15 is filled in the separation grooves 84 of the sacrifice layer 14. However, it is also possible to fill an entire vibration plate layer (lamination of the insulating layer 15, the vibration plate electrode layer 16 and the insulating layer 17) in the separation grooves 84. Therefore, normally, the width of the separation grooves 84 of the sacrifice layer 14 can be larger than the width of the separation grooves 82 of the electrode layer 12. As mentioned above, a level difference (step or unevenness) of the surface of the actuator forming member can be almost eliminated, and the effect of such is the same as that explained before.
As a material of the vibration plate electrode layer 16 which constitutes a part of the vibration plate 19, materials such as polysilicon, titanium silicide, tungsten silicide, molybdenum silicide, titanium nitride, aluminum, titanium, tungsten, molybdenum may be used for the same reason as the material of the electrode layer 12. Additionally, a transparent film such as an ITO film, a nesa film or a ZnO film can also be used. When the transparent film is used, the inspection inside the air gap 14a can be easily performed. Thus, an abnormality can be detected during a manufacturing process, which contributes to an attempt of cost reduction and improvement of reliability.
As mentioned above, the surface of the actuator forming member 10 (the surface of the vibration plate 19) can be substantially flat due to filling of the insulating layer 13 in the separation grooves 82 of the electrode layer 12, filing of the insulating layer 15 in the separation grooves 84 of the sacrifice layer 14, the sacrifice layer 14b being remained in the partition parts 50a, and etching of the sacrifice layer 14 through the sacrifice layer removing holes 60 formed in the vibration plate 19. Since the surface of the actuator is flattened, a resin film forming process can be performed, as mentioned later, for the purpose of acquiring an environment resistance (measures for high humidity) by sealing the sacrifice layer removing holes 60 and also acquiring a corrosion resistance of the vibration plate. Moreover, when it is necessary to join a separate member to the actuator device, such a joining process can be easily performed. As a result, the electrostatic actuator according to the present embodiment has little variation in properties and has high reliability. Additionally, the electrostatic actuator according to the present embodiment can be manufactured by mass production at a low cost.
In the example shown in
In the example shown in
In the example of
When the remaining sacrifice layer 14b of the partition part 50a is formed of an electrically conductive material like the above-mentioned examples, the remaining sacrifice layer 14b and the dummy electrodes 12b can be used as a part of electric wiring. If an electrostatic capacity of the partition part 50a raises a problem, the electrode 16 may be divided so that a part of the electrode 16 in the area of the partition part 50a is made into a dummy electrode.
The thus-formed dummy electrode can also be used as a part of electric wiring. By using these for wiring, each actuator element can be formed in a small area, which achieves a high-density integration. Thus the actuator can be manufactured at a low cost with high performance.
When using the remaining sacrifice layer 14b and the dummy electrode 12b as electric wiring, it is necessary to connect between electrodes electrically, and, thus, openings (through holes) are provided in the insulating layers 13, 15 and 17 beforehand. However, since a level difference is produced in an area where the through holes are formed, the through holes must be formed in an area where such a level difference does not cause a problem.
A description will now be given, with reference to
In the figures, the reference numeral 1 denotes a substrate for forming the actuator; 11 an insulating layer; 12a an electrode (may be referred to as an individual electrode); 12b a dummy electrode; 13 an insulating layer (may be referred to as an electrode side insulating layer); 14 a sacrifice layer; 15 an insulating layer (may be referred to as a vibration plate side insulating layer); 16 a vibration plate electrode layer; 17 an insulating layer also serves a stress-adjustment of the vibration plate; and 18 a resin film having a corrosion resistance to ink. Additionally, the reference numeral 19 denotes a vibration plate comprising the insulating layer 15, the vibration plate electrode layer 16, the insulating layer 17 and the resin film 18. Further, the reference numeral 14a denotes an air gap formed by removing parts of the sacrifice layer 14; “g” a distance of the air gap 14a; 50a a partition part; 14b a remaining sacrifice layer remaining in the partition part 50a; and 10 an actuator forming member in which the actuator is formed.
Additionally, the reference numeral 40 in the figures denotes a vibration plate movable area where the air gap 14a is formed, and 50 denotes a partition area, where the remaining sacrifice layer 14b is formed. Moreover, the alphabet “a” In
Although the partition width “f” is larger than the length “a” of the shorter side of the vibration plate in
As shown in
As shown in
As mentioned above, the vibration plate movable area 40 can be made flat by forming the sacrifice layer removing holes 60 in the vicinity of the partition parts 50a, which does not give an influence to the displacement of the vibration plate, for example, it is useful for a case in which the vibration plate movable area 40 is used as a mirror (an optical device mentioned later) or a case in which the vibration plate movable area 40 is used as a pressurizing chamber of an inkjet head.
Additionally, the sacrifice layer removing holes 60 are preferably arranged along a longer side of the vibration plate at an interval equal to or smaller than the length “a” of the shorter side of the vibration plate.
for example, when using as actuator of an inkjet head, the configuration (when viewed form above) of the actuator is preferably a rectangular shape since it is necessary to arrange a plurality of actuators with high density. It is general to take an arrangement in which adjacent actuators are aligned in a direction of the shorter side of the rectangular shape with the partition areas 50 therebetween. Also in many cases of other micro actuators, the actuator is made into a rectangular shape.
The etching of the sacrifice layer 14 is basically performed by isotopic etching, thus, normally, it is efficient that the sacrifice layer removing holes 60 are arranged in a grid pattern in the vibration plate movable area 40 at an equal interval. However, if the sacrifice layer removing holes 60 are located in the vibration plate movable area 40, the surface of the vibration plate cannot be formed in a flat surface, and it may influence the vibration characteristics of the actuator. Thus, it is preferable to arrange the sacrifice layer removing holes 60 in end portions along the longer side of the vibration plate 19 and in the vicinity of the partition parts 50a.
Additionally, when using as an actuator of an inkjet head, it is necessary to form a small air gap such as 2.0 μm so that the rigid vibration plate 19 must be deformed at a low voltage. Moreover, in order to use the vibration plate as a wall of an ink flow passage (pressurized liquid chamber), a sacrifice layer removing area (large opening) through which liquid leakage occurs must not be in the vibration plate. Therefore, although it is necessary to form the structure in which a plurality of small sacrifice layer removing holes 60 are arranged in the partition area as in the actuator according to the present invention, it has been considered that it is difficult to form a small air gap of a relatively large area according to a sacrifice layer removing process using small sacrifice layer removing holes 60.
However, it was found that an air gap of 0.2 μm to 2.0 μm can be formed by satisfying a structure, a processing method and a processing condition as explained below.
If the shorter side is set equal to or greater than 150 μm, unetched portion may remain in a portion remote from the sacrifice layer removing holes 60. If the etching process time is elongated so a to eliminate the unetched portion, there may occur a problem that a non-etching area (an area protected by a mask and not to be etched) is etched, or a portion to be left as the remaining sacrifice layer 14b is etched due to a failure of the etching stopper. Moreover, if the etching, process time is long, a process cost is increased, which causes a problem in mass production.
Moreover, from a viewpoint of etching of the sacrifice layer 14, it can be expected that the etching efficiency is more improved as the interval (pitch) c of the arranged sacrifice layer removing holes 60 is smaller. As mentioned above, since the etching for removing the sacrifice layer 14 is an isotropic etching, the interval “c” of the sacrifice layer removing holes 60 is preferably equal to or smaller than the length “a” of the shorter side of the vibration plate.
As shown in
On the other hand, if a<c as shown in
For the purpose of reference, arrangements of the sacrifice layer removing holes 60 different from that shown in
In the arrangement shown in
In the arrangement shown in
In the arrangement shown in
Larger size of the sacrifice layer removing holes 60 is more preferable in the viewpoint of etching of the sacrifice layer 14, however, smaller size is more preferable in the viewpoint of influence given to the vibration plate movable area, acquiring a strength of the partition parts 50a and sealing the sacrifice layer removing holes 60 by a resin film (mentioned later).
The minimum of the cross-sectional area of each sacrifice layer removing hole 60 is determined by the limitation in resolution in a photographic process and a limitation of etching for removing the sacrifice layer 14. Although detailed descriptions are omitted, as a result of evaluation in detail, it was found that the limitation in etching can be eliminated by arranging a plurality of sacrifice layer removing holes 60 along a plurality of lines. Thus, it was found that the size of the sacrifice layer removing holes 60 can be determined in accordance with the processing limitation. Since the sacrifice layer removing holes 60 are formed using a conventional semiconductor manufacturing process, it is preferable to set the cross-sectional area (an area viewed from the surface of the vibration plate) of each sacrifice layer removing hole 60 equal to or greater than 0.19 μm2. The upper limit of the size of each sacrifice layer removing hole 60 is mentioned later.
In the present embodiment, as shown in
Although acquisition of a corrosion resistance differs from the environment where the actuator is used, a resin layer is a useful protective film that has a corrosion resistance under various environments. When the actuator is used as a pressurizing element of an inkjet head, a film having a corrosion resistance to ink is necessary since the surface of the vibration plate is brought into contact with ink. Especially, in a case of an inkjet head using alkaline ink having a high pH value, a corrosion resistant film is indispensable, and a resin film as a film which is dissoluble in ink (no change in film thickness) and having a durability. Specifically, it was found that a polyimede film or a polybenzaoxazole (PBO) film is preferably used.
In the present embodiment, as shown in
In order to form the resin film in the structure shown in
When forming the resin film 18 by the spin coating method, the first important factor is the surface roughness of the member on which the resin film 18 is formed. If there is unevenness of an order of several microns, the resin film 18 cannot be formed uniformly. Thus, it must be attempted to reduce roughness or unevenness in the actuator forming area including at least the vibration plate movable area 40 and the partition area 50. Since the surface flatness, is achieved by the above-mentioned various structures and methods in the actuator according to the present invention, the resin film 18 can be well-formed on the vibration plate. In the present embodiment, it can be realized that the surface roughness or unevenness in the actuator forming area is in the order of 0.5 μm or less.
When forming the resin film 18 by a spin coating method, a surface wet control of the member on which the resin film 18 is formed is important. It is preferable that fluorine exists on the surface (fluorinated) on which the resin film 18 is formed. As for the method, there are a method for exposing to SF6 gas or xenon difluoride gas and a method of applying a plasma process. Since the surface containing fluorine decreases wet property against a resin film, the process mar-gin is improved and a yield rate and quality are improved.
In the present embodiment, the fluorinate process is performed using SF6 plasma. Thereby, the wet property against the resin film on the surface of the member is decreased, which prevents the resin film 18 entering the air gap 14a through the sacrifice layer removing holes 60, and the sacrifice layer removing holes 60 are filled by the resin film 18. Moreover, in the present embodiment, the etching for removing the sacrifice layer is performed by etching using SF6 plasma, and this etching process is used as the fluorinate process so as to simplify the process of manufacturing the actuator. The material to be used and the process flow are not limited to the above mentioned.
In the case where the resin film 18 is formed by the spin coating method, the configuration of the sacrifice layer removing hole 60 (the cross-sectional area an the length of the removing hole) is important.
Larger cross-sectional area of the sacrifice layer removing holes 60 is preferable from the viewpoint of etching for removing the sacrifice layer 14, however, smaller cross-sectional area is preferable from the viewpoint of suppressing influence to the vibration plate removal area 40 and sealing of the sacrifice layer removing holes 60 by the resin layer 18. As mentioned above, the lower limit of the cross-sectional area of the sacrifice layer removing hole 60 is 0.19 μm2 when considering etching for removing the sacrifice layer 14. On the other hand, the upper limit of the cross-sectional area of the sacrifice layer removing hole 60 is determined from the viewpoint of sealing the sacrifice layer removing hole 60, and it was found that the cross-sectional area be equal to or smaller than 10 μm2. As a result of various evaluations including the above-mentioned fluorinate process and a plasma process of a surface of which the resin film 18 is formed, it was found that it is possible to fill the resin film 13 in the sacrifice layer removing hole 60 and prevent the resin film material from entering the air gap 14a only when the cross-sectional area of the sacrifice layer removing hole 60 is equal to or smaller than 10 μm2.
Additionally, it was found that the fluorinate process and the plasma process of the surface prevents variation and contributes to improvement of a yield rate (preventing the resin film material from entering the air gap 14a).
Moreover, the length of the sacrifice layer removing hole 60, that is, a thickness t2 of the insulator layer (insulating layers 15 and 17) in which the sacrifice layer removing holes 60 are formed is preferably equal to or greater than 0.1 μm. If the thickness t2 of the insulator layer in which the sacrifice layer removing holes 60 are formed is less than 0.1 μm, a sufficient strength is not maintained and it is possible that the resin film enters the air gap 14a due to destruction of a periphery of the sacrifice layer removing holes 60 caused by an impact during a resin coating process. When the thickness of the insulator layer in which the sacrifice layer removing holes 60 are formed is equal to or greater than 0.1 μm, a periphery of the sacrifice layer removing holes 60 is not destructed and sealing can be done, which improves a yield rate of the manufacturing process.
There are various other methods, such as a vacuum deposition method, which form a corrosion resistant sealing film including the resin film. From among those methods, the spin coating method is conventional and inexpensive. According to the spin coating method, the resin film can be formed with uniform thickness of about 0.05 μm to several tens μm.
By realizing the formation of the resin film including the sealing of the sacrifice layer removing holes 60 using the spin coating method, a remarkable improvement in quality and cost reduction can be achieved. Moreover, the surface characteristic can be further improved by forming the resin film using the above-mentioned method.
Other structures and features of the actuator according to the present embodiment are the same as that of the above-mentioned embodiments that are explained with reference to
Next, a description will be given, with reference to
Here, the actuator substrate is produced by depositing, in turn, an electrode material, a sacrifice layer material and a vibration plate material onto the substrate 1.
First, as shown in
Subsequently, as shown in
Thus, the vibration plate 19 can be formed with a substantially flat surface having little unevenness un the subsequent process by dividing the sacrifice layer 14 by the separation grooves 84 and embedding the sacrifice layer 14 in the insulating layer 15 or the vibration plate, layer 19 (the insulation layer 15, the vibration plate electrode layer 16 and the insulating layer 1). Accordingly, the surface of the actuator substrate can be flattened and process design of subsequent processes becomes easy.
furthermore, as shown in
In the present embodiment, the insulating layer 17 is a laminated film, of a nitride film having a thickness of 0.15 μm and an oxide film having a thickness of 0.15 μm.
Next, as shown in
Although etching for removing the sacrifice layer 14 is performed by isotropic dry etching using SF6 gas, a wet etching using alkaline etching liquid such as KOH or TMAH may be used, or a dray etching using XeF2 gas may be used. Since the sacrifice layer (polysilicon) 14 is surrounded by an oxide film, the sacrifice layer 14 can be removed under a sacrifice layer removing condition which provides high electivity with respect to the oxide film, thereby forming the air gap 14a with sufficient accuracy. Moreover, the sacrifice layer 14b, which is separated by the insulating layer 15 filled in the separation grooves 64, is remained in each partition part 50a, which allows formation of a substantially flat surface of the actuator substrate.
It should be noted that since the etching for removing the sacrifice layer is isotropic etching, it is preferable to arrange the sacrifice layer removing holes 60 at an interval equal to or smaller than the length “a” of the shorter side of the air gap (movable vibration plate).
Then, as shown in
The formation of the resin film can be easily performed by a spin coating method. According to this approach, the resin film can be formed uniformly with sufficient accuracy of the thickness from about 0.05 μm to several 10 μm. Moreover, by forming the resin film according to the above-mentioned method, the surface characteristics can be further improved.
In the electrostatic actuator produced by the above-mentioned manufacturing method, the distance “g”; of the air gap can be defined by the thickness of the sacrifice layer 14, and, thus, the air gap 14a is formed with sufficient accuracy with little variation. Therefore, there is also little variation in the vibration characteristic (discharge characteristic) of the vibration plate 19. Moreover, since a large part of the actuator can be formed by a semiconductor process, a stable mass production can be achieved with sufficient yield.
Next, a description will be given, with reference to
In the fourth embodiment shown in
In the fourth embodiment shown in
Although a thin plate is used as the sealing member 41 in the present embodiment, the present invention is not limited to such a configuration and the sealing member may be a three-dimensional configuration object. As mentioned later, when using the actuator according to the present embodiment as an inkjet head, a flow passage formation member which forms an ink flow passage (channel) is joined as the sealing member.
In the fifth embodiment shown in
However, since a normal resin film has permeability slightly, if the actuator is put in a special environment which is not usually in a nature, rapid penetration of moisture may not be prevented. In the present embodiment, in order to solve such a problem, the sealing members are joined further so as to completely seal the sacrifice layer removing holes 60.
Although a thin plate is used as the sealing member 41 in the present embodiment, the present invention is not limited to such a configuration and the sealing member may be a three-dimensional configuration object. As mentioned later, when using the actuator according to the present embodiment as an inkjet head, especially when using ink having a high pH value, it is necessary to form a corrosion resistant film such as a resin film, and a flow passage formation member may be further joined after the formation of the resin film.
In the fourth and fifth embodiments, the sealing member 41 can be joined onto the vibration plate 19 since the surface on to which the sealing member 41 is joined is flattened by various structures and methods as explained in the above-mentioned embodiments.
A description will be now be given, with reference to
In the present embodiment, the electrode side insulating layer 13 and the vibration plate side insulating layer 15 are given variation in their thickness in the area where the air gap 14a exists. The thickness of each of the insulating layer 13 and the insulating layer 15 is set to be larger in a central part of the air gap in the cross section which is taken along a line parallel to the shorter side of the vibration plate and to be smaller at opposite ends of the air gap in the cross section.
In the electrostatic actuator, when a voltage is applied across the electrode 12a and the vibration plate electrode 16, an electrostatic attraction force is generated in a direction of the air gap distance g, thereby deforming the vibration plate 19 toward the electrode 12a. The vibration plate 19 in the vibration plate movable area 40 deforms in a generally Gaussian curve (convex when viewed from the electrode 12a) with the partition area 50 as fixed ends, and the deformation is maximize at the center of the vibration plate. In some cases, the deformed vibration plate 19 may contact the electrode 12a. In such a case, the central portion of the vibration plate 19 contacts first.
Moreover, the voltage across the electrode 12a and the vibration plate electrode 16 is divided into the insulating layer 13, the air gap 14a and the insulating layer 15 at a predetermined ratio. The predetermined ratio is determined in accordance with the thickness of each insulating layer, a dielectric constant of each insulating layer, an air gap distance and a dielectric constant of the air gap. A part of the voltage which acts as the electrostatic attraction force is determined by a part of the voltage distributed to the air gap. Accordingly, if the same voltage is applied, the electrostatic attraction force increases as the thickness of each of the insulating layers 13 and 15 is reduced relative to the air gap distance “g”. In other words, a low-voltage operation of the actuator can be attempted by reducing the thickness of the insulating layer 13 and/or the thickness of the insulating layer 15. On the other hand, in order to secure the electric reliability of the actuator (for example, an initial dielectric voltage withstand and a dielectric breakdown voltage with age), a certain thickness of the insulating layers is required.
According to the above-mentioned matters, a low-voltage operation of the actuator can be achieved, while maintaining reliability, by setting the thickness of each of the insulating layers 13 and 15 at the center portion thereof, in which the deformation of the vibration plate 19 is maximum, to a value which can provide sufficient electric reliability and reducing the thickness at the opposite end portions. There is no need to vary the thickens of both the insulating layers 13 and 15, and only the thickness of the insulating layer 13 may be varied or only the thickness of the insulating layer 15 may be varied. Or, the thickness of both the insulating layers 13 and 15 may be varied as shown in
Next, a description will be give, with reference to
The process of
The difference between the processes of
As for means to change the etching selection rate, there are means to change kinds of the insulating layers 13 and 15 and/or the sacrifice layer 14, means to change the film deposition condition and/or film deposition method, means to change the etching conditions of removing the sacrifice layer 14. Although means to change the etching conditions for removing the sacrifice layer 14 is used in the present embodiment, there are various approaches also in this means. For example, a mixture ratio or an amount of flow (an amount of use) of etchant may be changed, or a power supply of plasma may be changed. Unlike the example of
Next, the resist 70 is removed by oxygen plasma as shown in
Finally, as shown in
A description will now be given, with reference to
The inkjet head shown in
The bottom wall of the liquid pressurizing chamber 21 formed in the first substrate 1 serves as a vibration plate 19A. Individual electrodes 12a are formed below the vibration plate 19A so as to opposite to the vibration plate 19A with an air gap 14a therebetween. An electrostatic actuator is constituted by the vibration plate 19A and the individual electrodes 12a.
The vibration plate 19A has a two-layer structure comprising a nitride film 5a on the side of the electrodes 12a and a polysilicon film 5b which serves as a common electrode. As explained later, the air gap 14a is formed by etching a sacrifice layer 14 formed on the electrodes 12a after forming the electrodes 12a and the vibration plate 19A. Therefore, the electrode material of the vibration plate 19A is the polysilicon film, and a nitride film having a high selectivity to an etching gas is laminated as a protective film. Thereby, an electrode material having a low selectivity to etching gas can be used, which results enlargement of selection range of the process for forming the actuator substrate and cost reduction can be attempted.
The second substrate 4 joined to the bottom surface of the first substrate 1 serves as a protective substrate for protecting the first substrate 1.
Recessed parts 45 are formed in the second substrate 4 so as to form a cavity below the individual electrodes 12a corresponding to each air gap 14a. The recessed parts 45 are connected to each other by a connection groove (not shown in the figure). Additionally, each individual electrode 12a is partially removed so as to form connection through holes 46 so that the air gap 14a is connected to the cavity formed by the recessed part 45 through the connection through holes 46.
The cavity formed below the individual electrode 12a serves as a damper when air in the air gap 14a is compressed by a displacement of the vibration plate 19A. Thus, a pressure increase in the air gap 14a due to the displacement of the vibration plate 19A can be reduced, which results in a reduction in the drive voltage of the actuator.
The connection through holes 46 (corresponding to the sacrifice layer removing holes 60 in the above-mentioned embodiments) are used as through holes when etching a sacrifice layer formed between the electrodes 12a and the vibration plate 19A.
A pressure adjusting recessed part and a connection hole which connects the pressure adjusting recessed part to outside are also formed in the second substrate 4. Additionally, a movable plate for pressure adjustment is formed in the first substrate so as to form a wall of a cavity defined by the pressure adjusting recessed part. Accordingly, by closing the connection through holes 46 after supplying a dry air into the air gap 14a and the cavities defined by the recessed part 45 and the pressure adjusting recessed part, the actuator part is not influenced by an outside environment.
Next, a description will be give, with reference to
First, as shown in
Then, a polysilicon film 20 having a thickness of 0.5 μm is formed on the oxide film 5c. The polysilicon film 20 is used as a sacrifice layer, and the thickness of the polysilicon film 20 defines the distance (dimension) of the air gap 14a.
Further, an oxide film which serves as an insulating layer 13 and the individual electrode 12a are formed on the polysilicon film 20. As a material of the individual electrode 12a, polysilicon, aluminum, TiN, Ti, W, ITO, etc. can be used.
Subsequently, the individual electrode 12a is patternized by a lithography etching method, and the insulating layer 13 and the polysilicon film 20 are also patternized in necessary patterns.
Then, as shown in
Next, a3 shown in
Since the polysilicon film 20 which serves as a sacrifice layer is surrounded by the oxide films 13 and 5c, the sacrifice layer can be removed under a sacrifice layer etching condition providing a high electivity to the oxide films 13 and 5c, which results in an accurate formation of the air gap 14a. As for the method of removing the polysilicon film 20 serving as the sacrifice layer, a wet etching method using TMAH or a normal pressure dry etching method using XF2 gas may be used.
Additionally, although, in the present embodiment, the connection through holes 46 for removing the sacrifice layer are arranged in a grid pattern, the arrangement of the connection through holes 46 is not limited to the grid pattern. A large number of connection through holes 46 may decreases the area of the individual electrode 12a which results in a decrease in the electrostatic attraction force generated between the individual electrode 12a and the vibration plate 19A. Thus, it is necessary to select the number, the configuration and dimensions of the connection through holes 46 while attempting matching with the process of removing the sacrifice layer.
Thereafter, as shown in
It should be noted that, although not shown in the figures, finally the third substrate which is a nozzle forming member is joined to the surface of the first substrate, and the electrostatic inkjet head is completed. In the inkjet head produced by the above-mentioned manufacturing method, since the gap spacing is defied by the thickness of the sacrifice layer, the air gap can be formed with sufficient accuracy and little variation. Additionally, there is no need to perform a direct bonding of a anode bonding, and a large part of the manufacturing process is a semiconductor manufacturing process, the inkjet head having a stable performance can be manufactured at a sufficient yield rate.
A description will now be give of a droplet discharge head equipped with the electrostatic actuator according to the present invention.
The droplet discharge head equipped with the electrostatic actuator according to the present invention comprises: a nozzle forming member having a nozzle from which droplets of liquid are discharged; a flow passage forming member having a liquid pressurizing chamber connected to the nozzle; and an actuator forming member in which the electrostatic actuator according to the present invention is formed. The droplet discharge head according to the present invention can be used for a droplet discharge head which discharges a liquid resist in the form of a droplet, a droplet discharge head which discharge a sample of DNA in the form of a droplet or an inkjet head which discharges droplets of ink so as to print images or documents.
For example, the inkjet head comprises: one or more nozzle holes which discharge droplets of ink; a liquid pressurizing chamber (may be referred to as a discharge chamber, a pressurizing chamber, an ink chamber, a liquid chamber, a pressure chamber or an ink flow passage); a movable vibration plate which serves as a wall of the liquid pressurizing chamber; and an electrode facing the vibration plate with an air gap therebetween. An electrostatic attraction force is generated between the electrodes (vibration plate electrode and the electrode) by applying a voltage across the electrodes. Accordingly, the vibration plate is deformed by the electrostatic attraction force, and when the voltage is canceled, the vibration plate returns to its original state due to an elastic force. The returning motion of the vibration plate generates a pressure for pressurizing the ink in the liquid pressurizing chamber. Thus, a droplet of the ink is discharged from the nozzle hole by pressuring the ink in the liquid pressurizing chamber.
A description will now be given, with reference to
The inkjet head shown in
Although the flow restriction part 37 is formed on the nozzle forming member 30 in the present embodiment, the flow restriction part 37 may be provided in the flow passage forming member 20. Additionally, although the nozzle holes 31 are provided on the side surface (face surface) of the nozzle forming member 30, the inkjet head can be of an edge shooter type in which the nozzle holes are provided on an edge surface of the nozzle forming member 30 or an edge surface of the flow passage forming member 20.
In the figures, 1 denotes a substrate which forms ah actuator; 11 an insulating layer; 12a an electrode (may be referred to as individual electrode); 12b a dummy electrode; 14 a sacrifice layer; 15 an insulating layer (may be referred to as a vibration plate side insulating layer); 16 a vibration plate electrode layer; 17 an insulating layer which also serves as a stress-adjustment of a vibration plate; and 18 a resin film having a corrosion resistance against ink. Additionally, 19 denotes a vibration plate constituted by the insulating layer 15, the vibration plate electrode layer 16 and the insulating layer 17. Further, 14a denotes an air gap formed by removing a part of the sacrifice layer; “g” a distance of the air gap; 60 a sacrifice layer removing hole (through hole); 50a a partition part; 14b a remaining sacrifice layer which remains in the partition part 14b; and 10 an actuator forming part in which the actuator is formed.
The actuator forming part 10 or the eighth embodiment comprises: the substrate 1 which forms the actuator; the electrode layer 12 (electrodes 12a and dummy electrodes 12b) formed on the substrate 1; the partition parts 50a formed on the electrodes layer 12; the vibration plate 19 which is formed on the partition parts 50a and is deformable by an electrostatic force generated by a voltage applied to the electrodes 12a; and the air gap 14a formed between adjacent partition parts 50a. The air gap 14a is formed by removing by etching parts of the sacrifice layer 14 formed between the electrodes 12a and the electrodes 16 of the vibration plate 19. It is noted that other parts of the sacrifice layer 14, which are not removed by etching, remain in the partition parts 50a as the remaining sacrifice layer 14b.
The actuator forming member 10 is formed by repeating a film deposition and film processing (photo-lithography and etching) so as to form electrodes and insulation layers on a substrate having a high degree of cleanness. A high-temperature process may be used to form the actuator forming member by using silicon to make the substrate 1. It should be noted that the high-temperature process refers to a process for forming a high-quality film such as a thermal oxidizing method or a thermal nitriding method, a thermal CVD method which forms a high-temperature oxide film (HTO) or an LP-CVD method which forms a good-quality nitride film. By adopting the high-temperature process, high-quality electrode materials and insulating materials become usable, which can provide an actuator device having excellent conductivity and insulation. Moreover, the high-temperature process is excellent in controllability and reproducibility of a film thickness, thereby providing an actuator device having little variation in the electric properties. Further, since the controllability and reproducibility are excellent, process design becomes easy and a mass production at low cost can be achieved.
The electrode layer 12 is formed on the insulating layer 11 which is formed on the substrate 1, and is divided into each channel (each drive bit) by separation grooves B2. As shown by a part A3 encircled by a dotted line in
In order to completely fill the separation grooves 82 by the insulating layer 13, it is preferable to set a thickness of the insulating layer 13 equal to or greater than ½ of a width of the separation groove so as to form the surface of the insulating layer substantially flat. Or, it is preferable to set the width of the separation groove equal to or smaller than twice the thickness of the insulating layer. According to the above-mentioned relationship, the separation groove can be completely filled by the insulating layer, which results in a substantially flat surface of the insulating layer. Thus, since a surface level difference can be mostly eliminated by forming the insulating layer with a thickness equal to or greater than ½ of the width of the separation groove of the electrode layer, subsequent processes explained below, such as an air gap forming process, a resin film forming process or a joining process with other members, can be easily performed. As a result, an actuator having an air gap with an accurate distance thereof can be obtained, and, at the same time, it can be attempted to reduce a cost and improve reliability.
Here, as a material of the electrode layer 12 for forming the electrodes 12a, a compound silicide such as polysilicon, titanium silicide, tungsten silicide or molybdenum silicide or a metal compound such as titanium nitride may be preferably used. Since these materials can be deposited and processed with a stable quality and can be made into a structure which withstands a high-temperature process, there is less restriction with respect to temperatures in other processes. For example, a HTO (High-Temperature-Oxide) film or the like can be laminated on the electrode layer 12 as the insulating layer 13, the HTO film being an insulating layer having high reliability. Thus, the selection range can be enlarged, and cost reduction and improvement of reliability can be attempted. Additionally, a material such as aluminum, titanium, tungsten, molybdenum or ITO can also be used. By using these materials, a remarkable resistance reduction can be attempted, which results in reduction in a drive voltage. Additionally, since deposition and processing of films made of these materials can be easily achieved with a stable quality, cost reduction and improvement of reliability can be attempted.
Although the air gap 14a is formed by removing by etching parts of the sacrifice layer 14, other parts of the sacrifice layer 14, which parts are indicated by 14b and embedded in the partition parts 50a in
Since the distance “g” of the air gap 14a is accurately defined by the thickness of the sacrifice layer 14 by forming the air gap 14a by the removal of the parts of the sacrifice layer 14, variation in the distance “g” of the air gap 14a is extremely small, thereby achieving an accurate actuator having little variation in characteristics.
Additionally, since foreign substance is prevented from entering the air gap, it can be produced at a stable yield and a reliable actuator can be obtained.
Further, since the sacrifice layers 14b remain in the partition parts 50a and the vibration plate 10 is firmly fixed by the partition parts 50a, the accuracy of the distance “g” of the air gap 14a can be well-maintained and the actuator is excellent in structural durability. Moreover, since the sacrifice layer 14b remain in the partition parts 50a, there is little step or unevenness on the surface of the vibration plate 19, which results in substantially flat surface being formed on the actuator forming member 10. Thus, a formation of a resin film as mentioned later or a process for joining the actuator to other members can be easily performed, which results in cost reduction and improvement of reliability.
Here, as a material of the sacrifice layer 14, it is preferable to use polysilicon or amorphous silicon. These materials are most easily removable by etching, and it is preferable to use an isotropic dry etching method using SF6 gas, a dray etching method using XeF2 gas or a wet etching method using a solution of tetra methyl ammonium hydroxide (TMAH). Additionally, since polysilicon and amorphous silicon are generally-used, inexpensive materials and withstand a high temperature, a degree of freedom of a process in a subsequent process is also high. Further, since variation in the distance “g” of the air gap 14a, which is very important, can be extremely small by arranging silicon oxide films (insulating layers 13 and 15) having a high etching resistance above and below the sacrifice layer 14, an accurate actuator having little variation in properties can be obtained. Moreover, mass production is also easy at low cost.
As for a material of the sacrifice layer 14, titanium nitride, aluminum, silicone oxide or a resist material (for example, a photosensitive resin material used for photolithography) can be used. Although an etchant (etching material) and the air gap forming process depend on the material forming the sacrifice layer 14 and process difficulty and process cost thereof may also vary depending on the material of the sacrifice layer 14, the material of the sacrifice layer 14 can be selected based on its purpose.
When a silicone oxide film is used for the sacrifice layer 14, it is preferable to use polysilicon as a protective film (etching stopper) of the etching of the sacrifice layer. The polysilicon film may be commonly used for the electrode layer 12 and the vibration plate electrode layer. In order to remove the oxide film forming the sacrifice layer, it is preferable to use a wet etching method, a HF vapor method, a chemical dry etching method, etc. If an insulating layer is needed inside the air gap 14a, the insulating layer may be formed by oxidizing the polysilicon film remaining as an etching stopper. Thus, if a silicon oxide film is used as the sacrifice layer, the removal of the sacrifice layer can be performed by using etching materials used in semiconductor manufacturing processes. Additionally, if polysilicon films are formed on both sides of the sacrifice layer, a manufacturing process with little variation can be achieved. Further, the polysilicon film can be uses as an electrode as it is, which enables mass production at a low cost. Moreover, the thus-obtained actuator also provides high quality and accuracy.
Moreover, similar process can be achieved by various combinations of the material of the sacrifice layer and the etchant. For example, the sacrifice layer 14 may be removed by O2 plasma or an exfoliation liquid when a polymer material is used for the sacrifice layer 14. The sacrifice layer 14 may be removed by a liquid such as KOH when aluminum is used for the sacrifice layer 14. The sacrifice layer 14 may be removed by chemical such as a mixture solution of NH3OH and H2O2 when titanium nitride is used for the sacrifice layer 14.
The vibration plate 19 is constituted by a laminated film having the insulating layer 15, the vibration plate electrode layer 16 which serves as a common electrode and the insulating layer 17 which also serves as stress adjustment of the vibration plate, stacked in tern. It should be noted that the insulating layer 15 serves as a protective film (etching stopper) of etching the sacrifice layer, and contributes also as a protective film for leaving the sacrifice layer 14b of the partition parts 50a. The insulating layer 15 on the wail surfaces of the sacrifice layer 14b corresponds to a material that has been filled in separation grooves 84 formed in the sacrifice layer 14 during the manufacturing process.
Steps or unevenness formed on the surface of the insulating layer 15 can be made small by filling the insulating layer 15 in the separation grooves 84 which divide the sacrifice layer 14. Moreover, the sacrifice layer 14b can remain in the partition parts due to existence off the insulating layer 15 filled in the separation grooves 84. The effect of small steps or unevenness is as mentioned above.
Moreover, since the filled insulating layer is securely fixed to the wall surfaces of the sacrifice layer 14b, which results in the vibration plate 19 being firmly fixed by the partition parts 50a, an accuracy of the distance “g” of the air gap 14a of the thus-obtained actuator is high and also excellent in structural durability.
Additionally, similar to the case of filling the insulating layer 13 in the separation grooves 82 of the electrode layer 12, it is preferable to form the insulating layer 15 with a thickness equal to or less than ½ of the width of the separation grooves 84 of the sacrifice layer 14 in the case where the insulating layer 15 is filled in the separation grooves 94 of the sacrifice layer 14. The effect of such is the same as that explained before.
As a material of the vibration plate electrode layer 16 which constitutes a part of the vibration plate 19, materials such as polysilicon, titanium silicide, tungsten silicide, molybdenum silicide, titanium nitride, aluminum, titanium, tungsten, molybdenum may be used for the same reason as the material of the electrode layer 12. Additionally, a transparent film such as an ITO film, a nesa film or a ZnO film can also be used. When the transparent film is used, the inspection inside the air gap 14a can be easily performed. Thus, an abnormality can be detected during a manufacturing process, which contributes to an attempt of cost reduction and improvement of reliability.
As mentioned above, since the surface of the actuator forming member 10 (surface of the vibration plate 19) is made flat, the flow passage forming member 20 and the nozzle forming member 30 can be joined to the surface of the actuator forming member 10 with sufficient accuracy.
In the flow passage forming member 20, the liquid pressurizing chamber 21 is formed in a portion corresponding to the vibration plate movable portion (corresponding to the air gap 14a in the figure) of the actuator forming member 10, and the common liquid chamber 25 are formed for supplying ink to each liquid pressurizing chamber 21. Moreover, although not illustrated in the figure, an ink supply port connected to the common liquid chamber is provided so as to supply ink from outside.
In the present embodiment, the flow passage substrate 2 of the flow passage forming member 20 is formed of a nickel plate having a thickness of about 150 μm. For the purpose of simplification, the substrate 2 is formed by mechanical punching for the purpose of simplification, or formed by a known photographic process technique and a wet etching technique. As a material of the flow passage forming substrate 2, a stainless steel (SUS) substrate, a glass substrate, a resin plate or a resin film, a silicon substrate, or a lamination substrate of the aforementioned may be used. Especially, since a silicon (110) substrate can be etched by anisotropical etching in a perpendicular direction, it is very useful for forming a high-density head.
There are some methods of joining the flow passage forming member 20 to the actuator forming member 10. In a case of using an adhesive, as one example, the adhesive layer can be made thin by applying a pressing force, which results in a high assembling accuracy and high ink sealing. Therefore the joining method using an adhesive can provide a high-quality inkjet head.
The nozzle forming member comprises the nozzle substrate 3 formed of a nickel plate having a thickness of 50 μl. The nozzle holes 31 are provided on the surface part of the nozzle substrate 3 so the nozzle holes 31 are connected to the respective liquid pressurizing chambers 21. Additionally, grooves which correspond to the flow restriction parts 37 are provided on the surface of the nozzle substrate facing the flow passage forming member 20. As a material of the nozzle substrate 3, a stainless steel (SUB) substrate, a glass substrate, a resin plate or a resin film, a silicon substrate, or a lamination substrate of the aforementioned may be used.
Next, a brief description will be given of an operation of the thus-formed inkjet head. When a pulsed voltage of 40 V is applied from an oscillation circuit (drive circuit) to the electrode 12a in a state where the liquid pressurizing chamber 21 is filed by ink, the surface of the electrode 12a is charged with a positive potential. Accordingly, an electrostatic attraction force is generated between the electrode 12a and the vibration plate electrode 16, thereby deforming or bending the vibration plate 19 toward the electrode 12a. Thus, the pressure in the liquid pressurizing chamber 21 is decreased, which allow ink to flow into the liquid pressurizing chamber 21 from the common liquid chamber 25 through the flow restriction part 37.
Thereafter, when the pulsed voltage is decreased to zero, the vibration plate 19, which has been deformed by the electrostatic force, returns to its original shape due to its elasticity. Consequently, the pressure of the ink in the liquid pressurizing chamber 21 rises rapidly, and a droplet of ink is discharged from she nozzle hole 31 toward a recording paper as shown in
Here, the electrostatic attraction force generated between the vibration plate electrode 16 and the electrode 12a increases in inverse proportion to the distance between the electrodes. Thus, it is important to form a small distance of the air gap 14a (air gap distance g) between the electrode 12a and the vibration plate 19.
Then, as mentioned above, a small air gap can be formed with sufficient accuracy by forming the air gap 14a by the sacrifice layer etching method
A description will now be given, with reference to
In this process, the actuator is produced by sequentially depositing an electrode material, a sacrifice layer material and a vibration plate material on the actuator substrate 1.
First, as shown in
Subsequently, as shown in
Thus, the vibration plate 19 can be formed with a substantially flat surface having little unevenness un the subsequent process by dividing the sacrifice layer 14 by the separation grooves 84 and embedding the sacrifice layer 14 in the insulating layer 15 or the vibration plate layer 19 (the insulation layer 15, the vibration plate electrode layer 16 and the insulating layer 17). Accordingly, the surface of the actuator substrate can be flattened and process design of subsequent processes becomes easy.
Furthermore, as shown in
Subsequently, the insulating layer 17 is formed with a thickness of 0.3 μm. The insulating layer 17 serves as a stress adjustment (bending prevention) film for preventing the vibration plate from being bent or deformed. In the present embodiment, the insulating layer 17 is a laminated film of a nitride film having a thickness of 0.15 μm and an oxide film having a thickness of 0.15 μm.
Next, as shown in
Then, the etching for removing the sacrifice layer 13 is performed by isotropic dry etching using SF6 gas. It should be noted that a wet etching using alkaline etching liquid such as KOH or TMAH may be used, or a dray etching using XeF2 gas may be used.
Since the sacrifice layer (polysilicon) 14 is surrounded by an oxide film, the sacrifice layer 14 can be removed under a sacrifice layer removing condition which provides high, electivity with respect to the oxide film, thereby forming the air gap 14a with sufficient accuracy.
Moreover, the sacrifice layer 14b, which is separated by the insulating layer 15 filled in the separation grooves B4, is remained in each partition part 50a, which allows to form a substantially flat surface of the actuator substrate.
It should be noted that since the etching for removing the sacrifice layer is isotropic etching, it is preferable to arrange the sacrifice layer removing holes 60 at an interval equal to or smaller than the length “a” of the shorter side of the air gap (movable vibration plate).
Thereafter, as shown in
Thereafter, as shown in
Further, since the surface of the actuator forming member 10 is flat, the flow passage part (the liquid pressurizing chamber and the flow restriction part) can be formed by a photosensitive polyimide or DFR applied by a spin coating method. In such a case, although illustration is omitted, it is not necessary to prepare the fluid passage forming member separately. Moreover, in the case of the inkjet head using alkaline ink with a high pH value, it is preferable to provide a corrosion resistant resin film on the uppermost layer of the vibration plate.
As mentioned above, since the droplet discharge head according to the present embodiment comprises the nozzle forming member 10 having the nozzle for discharging droplets of liquid, the flow passage forming member 20 having the liquid pressurizing chamber connected to the nozzle, and the actuator forming member which pressurizes a liquid in the liquid pressurizing chamber, and the actuator forming member is the electrostatic actuator according to the present invention, the thus-obtained droplet discharge head has little variation in the liquid injecting characteristic and is reliable and manufactured at a low cost.
It should be noted that as a liquid injecting head, in addition to the inkjet head equipped with the electrostatic actuator according to the present invention, the electrostatic actuator head according to the present invention may be used for a droplet discharge head which discharges a liquid resist as a droplet discharge head which discharges a liquid other than ink. Additionally, the droplet discharge head according to the present invention may be used as a droplet injecting head which is equipped to a color filter manufacturing apparatus for manufacturing a color filter of a liquid crystal display. Moreover, the droplet discharge head according to the present invention may be used as a liquid injecting head which is equipped to an electrode forming apparatus for forming electrodes of an organic electro-luminescence (EL) display or a face luminescence display (FED). In this case, the electrode material such as an electrically conductive paste is injected. Further, the droplet discharge head according to the present invention may be used as a liquid injecting head which is equipped to a biochip manufacturing apparatus for manufacturing a biochip. In this case, the droplet discharge head discharges a sample of a biological organic material or the like. Further, the droplet discharge head according to the present invention is applicable to a liquid injecting head of industrial use other than the above-mentioned liquid injecting heads.
Next, a description will be given, with reference to
The ink-cartridge integrated head 100 according to the present invention comprises an inkjet head 102 according to one of the above-mentioned embodiments having a nozzle hole 101 and an ink tank 103 for supplying ink to the inkjet head 101. The inkjet head 102 and the ink tank 103 are integrated with each other. Thus, if integrating the ink tank for supplying ink with the droplet discharge head according to the present invention, an ink-cartridge integrated with a reliable droplet discharge head (ink tank integrated head) having little variation in droplet discharging properties can be achieved at a low cost.
Next, a description will be given, with reference to
The inkjet recording apparatus shown in FIG. 26 has an apparatus body 111. Accommodated in the apparatus body 111 is a printing mechanism 112 comprising a carriage movable in a main scanning direction, a recording head according to the present invention mounted on the carriage, and an ink-cartridge for supplying ink to a recording head. A paper feed cassette (or a paper feed tray) 114 can be removable attached to a lower part of the apparatus body 111 so as to be freely inserted or removed from the front side. Additionally, a manual feed tray 115 is pivotally provided for manually feeding a print paper. Print papers 113 are fed from the paper feed cassette 114 or the manual feed tray 115. The print paper 113 on which a desired image is recorded by the printing mechanism 112 is ejected onto a paper eject tray 116 attached to the rear side of the apparatus body 111.
The printing mechanism part 112 has a main guide rod 121 extending between left and right side plates (not shown) and a sub guide rod. A carriage 123 is movably supported by the main guide rod 121 and the sub guide rod 122 in the main scanning direction (a direction perpendicular to the paper face of
The ink-cartridge 125 is provided with an atmosphere port connected to an atmosphere en upper portion thereof and a supply port for supplying ink to the inkjet head on a lower part thereof, and a porous material filled by ink is provided inside thereof. The ink-cartridge 125 maintains the ink supplied to the inkjet head at a slightly negative pressure according to the capillary force. Although the heads 124 of each color are used as a recording head in this example, a single head h having a nozzle which discharges ink droplets of each color. The backside (a downstream side in the paper feed direction) of the carriage 123 is engaged with the main rod guide 121, and the front side (an upstream side of the paper feed direction) is slidably engaged with the sub guide rod. In order to move and scan the carriage 123 in the main scan direction, a timing belt 130 is provided between a drive pulley 128 driven by a main scan motor 127 and an idle pulley 129. The timing belt 130 is fixed to the carriage 123 so that the carriage 123 is reciprocally movable in response to normal and reverse rotations of the main scan motor 127. In order to feed the print papers 113 accommodated in the paper feed cassette 114 to a position under the heads 124, the apparatus is provided with: a feed roller 131 and a friction pad 132 that separate and feed each print paper 113 from the paper feed cassette 114; a guide member guiding each print paper 113; a convey roller 134 which reverses and conveys each print paper 113; a convey roller 135 which is pressed against the circumference surface of the convey roller 134; and an end roller 136 which defines a feed angle of each print paper 113 fed by the convey roller 134. The convey roller 134 is rotationally driven by a sub scan motor 137 via a train of gears.
Also provided is a platen member 139 which serves as a print paper guide member. The platen member 139 guides each print paper 113 fed from the convey roller 134 under the recording heads 124 in response to a moving range of the carriage 123 in the main scanning direction. On the downstream side of the platen member 139 in the paper feed direction, a convey roller 141 which is rotationally driven for feeding each print paper 113 in a paper eject direction and an idle roller 142 are provided. Further, an paper eject roller 143 and an idle roller 144 that eject each print paper onto the paper eject tray 116 are provided, and also guide members 145 and 146 are provided for defining a paper eject path.
When recording, the recording heads 124 are driven in response to image signals while moving the carriage 123. Thereby, ink is discharged toward the print paper 113 which is stopped so as to record one line, and, then, receding of a next line is performed after feeding the print paper 113 by a predetermined distance. Upon receipt of a recording end signal or a signal which indicates that the trailing edge of the print paper 113 reaches a recording area, the recording operation is ended and the print paper 113 is ejected.
A recovery device 147 for recovering discharge failure of the heads 124 is located at a position outside the recording area on the right end side in the moving direction of the carriage 123. The recovery device 147 has a capping means, a suctioning means and a cleaning means. The carriage 123 is moved to the side of the recovery device 147 during print standby, and the heads 124 are capped by the capping means. Thereby, a discharge port part is maintained at a wet state, which prevents generation of discharge failure due to dry ink. Additionally, by discharging ink, which is not used for recording, during the recording, viscosity of ink at all discharge ports is maintained constant, thereby maintaining a stable discharge performance.
When a discharge failure occurs, the discharge ports (nozzles) of the heads 124 are sealed with the capping means. Then, air bubbles etc. are suctioned out of the discharge ports together with ink by the suctioning means. Additionally, ink and dusts adhering to the discharge port surface are removed by the cleaning means. Thereby, a discharge failure is recovered. The suctioned ink is ejected to a waste ink reservoir (not shown in the figure) and is absorbed by an ink-absorbing material in the waste ink reservoir.
Thus, since the above-mentioned inkjet head is equipped with the inkjet head which is the droplet discharge head according to the present invention, there is little variation in the discharge characteristic of ink droplet and recording of high-quality images can be achieved.
Although, in the above description, the inkjet recording apparatus equipped with the inkjet head using the electrostatic actuator according to the present invention is explained, the electrostatic actuator head according to the present invention may be used for a droplet discharge apparatus which discharges a liquid resist as a droplet. Additionally, the droplet discharge apparatus according to the present invention may be used as a liquid injecting apparatus which is used for a color filter manufacturing apparatus for manufacturing a color filter of a liquid crystal display. Moreover, the droplet discharge apparatus according to the present invention may be used as a liquid injecting apparatus for an electrode forming apparatus which forms electrodes of an organic electro-luminescence (EL) display or a face luminescence display (FED). In this case, the liquid injecting apparatus injects an electrode material such as a conductive past from a droplet discharge head. Further, the droplet discharge apparatus according to the present invention may be used as a liquid injecting apparatus for a biochip manufacturing apparatus for manufacturing a biochip. In this case, the liquid injecting apparatus discharges a sample of DNA, a biological organic material or the like in the form of a droplet. Further, the liquid injecting apparatus according to the present invention is applicable to a liquid injecting apparatus of industrial use other than the above-mentioned liquid injecting apparatuses.
A description will now be given, with reference to
Next, a description will be given of a principle of operation of the micro pump. Like the case of the inkjet head mentioned above, by giving a pulsed potential selectively to the electrodes 224, an electrostatic attraction force is generated between the vibration plate 222, and each deformable part 222a of the vibration plate 222 deforms toward the electrode 224. If the deformable parts 222a are driven sequentially one after another from the right side in the figure, the fluid in the flow passage flows in a direction of arrow, which enables transportation of the fluid.
In this example, the small micro pump of a low power consumption with little variation in characteristic is obtained by being equipped with the electrostatic actuator according to the present invention. It should be noted that although a plurality of deformable parts are formed in the vibration plate in this example, the number of deformable parts may be one. Moreover, in order to improve a transport efficiency, one or more valves such as, far example, check valves may be provided between the deformable parts.
A description will now be given, with reference to
The actuator substrate 302 comprises the deformable mirror 301 (corresponding to the vibration plate of the head) provided on a base substrate 321 and electrodes 324 facing respective deformable parts 301a of the mirror 301 with a predetermined air gap therebetween. The surface of the mirror 301 is formed in a substantially flat surface. The actuator substrate 302 has the same structure as the structure explained in the above-mentioned embodiment of the inkjet head except for the vibration plate having the mirror surface, and descriptions thereof will be omitted.
Here, the principle of the optical device is explained. Similar to the above-mentioned inkjet head, an electrostatic force is generated between the electrodes 324 and the respective deformable parts 301a of the mirror 301 by selectively applying the electrodes 324, and, thereby, the deformable parts 301a of the mirror 301 are deformed in a concave form and turn to concave mirrors. Therefore; when a light from a luminous source 310 is irradiated onto the mirror 301 through a lens 311 and the mirror 301 is not driven, light is reflected at art angle the same as the incident angle. On the other hand, when the mirror is driven, the driven deformable parts 301 turn to concave mirrors and the reflected light becomes a scattered light. Thereby, an optical modulation device is achieved.
Therefore, the small optical device of a low power consumption can be obtained with little variation 1 in characteristic by being equipped with the electrostatic actuator according to the present invention.
A description will be given, with reference to
Therefore, like the structure shown, in
It should be noted that, in addition to the above-mentioned micro pump and optical device (optical modulation device), the electrostatic actuator according to the present invention is applicable to an actuator (optical switch) of a multi optical lens, a micro flow meter, a pressure sensor, etc.
The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2002-228117 | Aug 2002 | JP | national |
| 2002-262345 | Sep 2002 | JP | national |
| 2002-264243 | Sep 2002 | JP | national |
| 2002-266332 | Sep 2002 | JP | national |
| 2002-270139 | Sep 2002 | JP | national |
| 2002-341752 | Nov 2002 | JP | national |
This application is a divisional of U.S. Ser. No. 10/521,055, filed Jan. 12, 2005 now U.S. Pat. No. 7,416,281, which in turn is a Section 371 national stage of International Application No. PCT/JP2003/009929, filed Aug. 5, 2003, the entire contents of which are incorporated herein by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
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