Patent Application
20080151008
This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2006-342339 filed Dec. 20, 2006.
1. Technical Field
The present invention relates to a liquid droplet ejecting head, an image forming device, and a method of manufacturing a liquid droplet ejecting head.
2. Related Art
There have conventionally been known inkjet recording devices which selectively eject ink droplets from plural nozzles of an inkjet recording head (hereinafter, simply called “recording head” upon occasion) serving as a liquid droplet ejecting head which moves reciprocally in a main scanning direction, and print characters, images and the like onto a recording medium such as a recording sheet or the like which is conveyed-in along a sub scanning direction.
In developing low-cost, piezo-type (piezoelectric element) recording heads of high resolutions of 1200 dpi and, further, 2400 dpi as next-generation recording heads, in order to address the demand for improvements in the printing quality, the printing speed, and the like of the printer, research aiming for decreased size and higher density, operation at a lower voltage, and higher-speed response of the piezoelectric elements has progressed.
Among these, in the case of the structure of a piezoelectric element which is formed by patterning a lower electrode, it is important to make the thickness of the substrate, which becomes the vibrating plate on which a piezoelectric body is formed, thin in order to improve the displacement efficiency. However, if the substrate overall is made to be thin, there is the contradictory relationship that the rigidity of the substrate decreases and the stability of displacement worsens.
Further, by making the piezoelectric elements high density, the influence with respect to the piezoelectric elements by the rigidity of the substrate increase, accordingly, the dispersion in displacement efficiency among the respective piezoelectric elements becomes large when the rigidity of the substrate decreases.
An aspect of the present invention is a liquid droplet ejecting head including: a nozzle that ejects a liquid droplet; a pressure chamber that is connected to the nozzle; a vibrating plate that forms one portion of the pressure chamber; a lower electrode that is formed on a surface of the vibrating plate, and exhibits one polarity; a piezoelectric body that is flexurally-deformable, formed on a surface of the lower electrode, and disposed at a position facing the pressure chamber with the vibrating plate therebetween; and an upper electrode that is formed at a surface of the piezoelectric body opposite the surface at which the lower electrode is formed, the upper electrode exhibiting another polarity, when viewed from a direction perpendicular to the surface of the lower electrode, the piezoelectric body being provided further toward an inner side than a peripheral wall of the pressure chamber, and the lower electrode being of a size such that one portion thereof overlaps with the peripheral wall of the pressure chamber, and being individuated per each piezoelectric body.
Exemplary embodiments of the invention will be described in detail with reference to the following figures, wherein:
Hereinafter, preferred exemplary embodiments of the present invention will be described in detail on the basis of the examples illustrated in the drawings. Note that description will be given by using an inkjet recording device 10 as an example of an image forming device. Accordingly, description is given with the liquid being an ink 110, and the liquid droplet ejecting head being an inkjet recording head 32. Further, description is given with the recording medium being a recording sheet P.
As shown in
The sheet supplying section 12 is structured with a stocker 24 in which the recording sheets P are layered and stocked, and a conveying device 26 which pulls the recording sheet P one-by-one from the stocker 24 and conveys it to the registration adjusting section 14. The registration adjusting section 14 includes a loop forming portion 28 and a guide member 29 which controls the posture of the recording sheet P. Due to the recording sheet P passing through this section, the skew is corrected by utilizing the stiffness of the recording sheet P, and the conveying timing is controlled, and the recording sheet P is supplied to the recording section 20. Further, via a sheet discharging belt 23, the discharging section 22 accommodates the recording sheet P, on which an image has been formed at the recording section 20, at a tray 25.
A sheet conveying path 27 along which the recording sheet P is conveyed is structured between the recording head portion 16 and the maintenance portion 18 (the sheet conveying direction is shown by arrow PF). The sheet conveying path 27 includes star wheels 17 and conveying rollers 19, and continuously (without stoppage) conveys the recording sheet P while nipping the recording sheet P between the star wheels 17 and the conveying rollers 19. Ink droplets are ejected from the recording head portion 16 onto the recording sheet P, and an image is formed on the recording sheet P. The maintenance portion 18 includes maintenance devices 21 which are disposed so as to oppose inkjet recording units 30, and carries out processings such as capping, wiping, preliminary ejecting, suctioning, and the like on the inkjet recording heads 32 (see
As shown in
An image is recorded on the recording sheet P by ink droplets being ejected from the nozzles 56 onto the recording sheet P which is conveyed continuously along the sheet conveying path 27. Note that at least four of the inkjet recording units 30 are disposed in correspondence with the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) in order to record a so-called full-color image for example.
As shown in
Here, the basic printing region width is the maximum width among recording regions from which margins, at which printing is not carried out, are subtracted from the both ends of the recording sheet P, and generally, is larger than the maximum sheet width PW which is the object of printing. This is because there is the concern that the recording sheet P will be conveyed while inclined at a predetermined angle with respect to the conveying direction (i.e., while skewed), and because the demand for borderless printing is high.
Next, the inkjet recording head 32 in the inkjet recording device 10 of the above-described structure will be described in detail. Note that
As shown in
The volume of the ink pooling chamber 38 is regulated by the ceiling plate 40 and a partitioning wall 42. Plural ink supply ports 36 are formed in lines at predetermined places of the ceiling plate 40. Further, air dampers 44 (a photosensitive dry film 96 which will be described later), which are made of resin and mitigate pressure waves, are provided in the ink pooling chamber 38, further toward the inner side than the ceiling plate 40 and between the ink supply ports 36 which form the lines.
Any material, such as glass, ceramic, silicon, resin, or the like for example, may be used as the material of the ceiling plate 40, provided that it is an insulator which has strength such that it can become the support of the inkjet recording head 32. Further, metal wires 90, which are for energizing driving ICs 60 which will be described later, are provided at the ceiling plate 40. The metal wires 90 are covered and protected by a resin film 92, such that erosion of the metal wires 90 by the ink 110 is prevented.
The partitioning wall 42 is molded of resin (a photosensitive dry film 98 which will be described later), and partitions the ink pooling chamber 38 into a rectangular shape. Further, the ink pooling chamber 38 is separated vertically from the pressure chambers 50 via the piezoelectric elements 45 and vibrating plates 48 which are flexurally deformed in the vertical direction by the piezoelectric elements 45. Namely, the piezoelectric elements 45 and the vibrating plates 48 are structured so as to be disposed between the ink pooling chamber 38 and the pressure chambers 50, and the ink pooling chamber 38 and the pressure chambers 50 are structured so as to not exist on the same horizontal plane.
Accordingly, the pressure chambers 50 can be disposed in states of being near to one another, and the nozzles 56 can be disposed at a high density in the form of a matrix. The vibrating plate 48 is a three-layer structure formed by SiO2 films, to which no impurities are added, being layered on and beneath a silicon oxide film (SiO2 film) to which germanium (Ge) is added, by Plasma-Chemical Vapor Deposition (P-CVD). The vibrating plate 48 is elastic at least in the vertical direction. When the piezoelectric element 45 is energized (i.e., when voltage is applied to the piezoelectric element 45), the vibrating plate 48 flexurally deforms (is displaced) in the vertical direction. Other than this, a layered film of silicon and silicon oxide films, or the like, may be used as the vibrating plate. In this case, the vibrating plate is fabricated by using an SOI wafer as the base substrate. Note that the thickness of the vibrating plate 48 is greater than or equal to 1 μm and less than or equal to 20 μm (1 μm to 20 μm) in order to obtain stable rigidity.
The piezoelectric element 45 is adhered to the top surface of the vibrating plate 48, at each of the pressure chambers 50. Lower electrodes 52, which are one polarity of the piezoelectric elements 45, are disposed at the bottom surfaces of piezoelectric bodies 46 structuring the piezoelectric elements 45. Upper electrodes 54, which are the other polarity, are disposed on the top surfaces of the piezoelectric bodies 46.
Here, the piezoelectric body 46 and the upper electrode 54 are provided at the inner side of the peripheral (surrounding) wall (a silicon substrate 72 which will be described later) of the pressure chamber 50. The lower electrodes 52 are provided individually at each piezoelectric body 46. Further, the lower electrodes 52 is of a size such that a longitudinal direction one end portion of the lower electrode 52 reaches a peripheral wall of the pressure chamber 50 (the longitudinal direction one end portion of the lower electrode 52 overlaps with the peripheral wall).
The upper electrodes 54, the piezoelectric bodies 46, and the lower electrodes 52 are covered and protected by a low water permeable insulating film (hereinafter called “SiOx film”) 80 which serves as a protective film.
Further, the top surface of the low water permeable insulating film (SiOx film) 80 and metal wires 86, 87 are covered and protected by a resin protective film 88, such that erosion due to the ink 110 is prevented.
At the regions above the piezoelectric elements 45, the resin protective film 88 is formed to be thin. Further, the air damper 44 (the photosensitive dry film 96 which will be described later), which is formed of resin and mitigates pressure waves, is provided at the top surface of the resin protective film 88 positioned above the piezoelectric element 45, so as to oppose the piezoelectric element 45.
On the other hand, the driving ICs 60 are disposed at the outer sides of the ink pooling chamber 38 which is prescribed by the partitioning wall 42, and between the ceiling plate 40 and the vibrating plates 48. The driving ICs 60 are structured so as to not be exposed (not project out) from the vibrating plates 48 or the ceiling plate 40.
The peripheries of the driving ICs 60 are sealed by a resin material 58. Plural injection openings 40B for the resin material 58 which seals the driving ICs 60 are formed in the ceiling plate 40 in the manufacturing step shown in
As shown in
Bumps 64 are provided at the outer sides of the driving ICs 60 in
Accordingly, the metal wires 90 of the ceiling plate 40 are energized from the main body of the inkjet recording device 10, and the metal wires 87 are energized from the metal wires 90 of the ceiling plate 40 via the bumps 64, and the driving ICs 60 are energized therefrom. Voltages are applied to the piezoelectric elements 45 at predetermined times by the driving ICs 60, such that the vibrating plates 48 are flexurally deformed in the vertical direction. The ink 110 filled in the pressure chamber 50 is thereby pressurized, and ink droplets are ejected from the nozzles 56.
One nozzle 56 which ejects the ink droplets is provided for each pressure chamber 50, at a predetermined position thereof. The pressure chamber 50 and the ink pooling chamber 38 are connected by an ink flow path 66 and a communicating path 115 being connected. The ink flow path 66 sidesteps the piezoelectric element 45 and passes through the vibrating plate 48. The communicating path 115 extends horizontally in
Next, the manufacturing processes of the inkjet recording head 32, which is structured as described above, will be described in detail on the basis of
As shown in
Next, as shown in
Thereafter, as shown in
The thermal expansion coefficient of this glass paste 76 is 1×10−6/° C. to 6×10−6/° C., and the softening point thereof is 550° C. to 900° C.
After the filling of the glass paste 76, the silicon substrate 72 is subjected to heating processing, for example, at 800° C. for 10 minutes. The temperature which is used in the curing by heat treatment of the glass paste 76 is a temperature which is higher than the film forming temperature of the piezoelectric elements 45 (e.g., 550° C.) and the film forming temperature of the vibrating plate 48 (e.g., 700° C.) which will be described later. The glass paste 76 is made to be resistant to the high temperatures in the film forming (deposition) processes of the vibrating plate 48 and the piezoelectric elements 45.
Namely, temperatures up to the temperature at which at least the glass paste 76 is cured by heat treatment can be used in later processes. Thereafter, the top surface (obverse) of the silicon substrate 72 is polished and the excess glass paste 76 is removed, such that the top surface (obverse) is planarized.
Next, as shown in
Then, as shown in
Specifically, film-formation is carried out by adding tetramethyl germanium (TMGe) which is an alkoxide gas to a gas containing oxygen (O2) and silicon (Si) raw materials, e.g., a gas containing any of tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), or silane (SiH4). Note that, at this time, the thickness of the SiO2 film to which Ge is added is made to be greater than or equal to ½ of the entire thickness of the vibrating plate 48. Note that Si, SiN, or the like may be used, instead of SiO2, as the material structuring the vibrating plate 48.
When the SiO2 films have been continuously film-formed in this way, they are annealed (thermally processed) in a nitrogen (N2) atmosphere for one hour at a temperature, e.g., 700° C., which is higher than the maximum temperature in the processes thereinafter. Note that the annealing temperature is not limited to 700° C., and it suffices for the annealing temperature to be greater than or equal to 600° C. and less than or equal to 1100° C. (600° C. through 1100° C.).
When the SiO2 films are film-formed and annealed such that the vibrating plate 48 of the three-layer structured is formed, as shown in
Then, as shown in
Specifically, it is carried out by sputtering of the PZT film (film thickness: 5 μm), sputtering of the Ir film (film thickness: 0.5 μm), resist formation by photolithography, etching (dry etching using a Cl2 or an F gas), and resist removal by oxygen plasma. The materials of the lower electrodes 52 and the upper electrodes 54 have high affinity with the PZT material which is the piezoelectric bodies 46, and are heat-resistant. Examples include Ir, Ru, Pt, Ta, and IrO2, RuO2, PtO2, TaO4, and the like which are oxides thereof. Further, the film-forming temperature of the PZT film 65 is 550° C., and an AD method, a sol-gel method, or the like also can be used in the layering (film-forming) of the PZT film 65.
Next, as shown in
In this way, in the process of forming the piezoelectric elements 45, the vibrating plate 48 is formed of SiO2 at the silicon substrate 72, and the layered film 63 (lower electrodes 52) of Ir and Ti are formed on the top surface thereof. Then, the PZT film 65 (piezoelectric bodies 46) is formed on the top surface of the layered film 63, and the Ir film 67 (the upper electrodes 54) is formed on the top surface of the PZT film 65, such that a plate of a five-layer structure is formed. Then, the piezoelectric elements 45 are formed by respectively patterning the upper electrodes 54, the piezoelectric bodies 46, and the lower electrodes 52.
Next, as shown in
Note that, although the SiOx film 80 (silicon oxide film) is used as the protective film in this case, an SiNx film (silicon nitride film), an SiOxNy film, or the like may be used. Further, SOG (Spin-On-Glass), a metal film of Ta, Ti, or the like, a metal oxide film of TaO2, Ta2O5 or the like, a resin film, or the like may be used. The protective film may be a single layer film of any of these, or a multilayer film combining these. Oxide films, nitride films, SOG, metal films, and metal oxide films have excellent insulating ability, moisture-resistance, and an ability to suppress (mitigate) steps between the film layers, and thereamong, oxide films, nitride films, SOG and metal films have excellent chemical (ink) resistance as well.
Then, as shown in
Next, as shown in
Then, as shown in
Note that the resin protective film 88 being of the same type of resin material as the partitioning wall 42 (the photosensitive dry film 98) which will be described later is preferable because the joining force to the partitioning wall 42 (the photosensitive dry film 98) is strong, and the penetration of the ink 110 from the boundary surfaces thereof is prevented even more, and, because the coefficients of thermal expansion thereof are substantially equal, there is also the advantage that little thermal stress arises.
As shown in
Next, as shown in
Next, as shown in
Then, as shown in
After the partitioning wall 42 and the bumps 64 are formed, as shown in
Next, as shown in
Next, as shown in
Then, as shown in
Note that, although a liquid containing HF is used in the removal of the glass paste 76 here, a gas or vapor containing HF may be used in the removal of the glass paste 76.
A dissolving solution for the Ge film 78, e.g., hydrogen peroxide (H2O2) which is heated to 60° C. for example, is supplied from the pressure chamber 50 side, and portions of the Ge film 78 are removed by etching. At this stage, the pressure chambers 50 and the communication paths 115 are completed. When the Ge film 78 is removed by etching in this way, at regions other than where the pressure chambers 50 and the communication paths 115 are formed, there is no particular problem in leaving the Ge film 78 as is.
Then, as shown in
In this way, the inkjet recording head 32 is completed, and, as shown in
For example, in the present exemplary embodiment, after the ceiling plate 40 is joined (united) to the resin film 92 and the metal wires 90 in
Further, in the present exemplary embodiment, the silicon substrate 72 is opened by RIE, the glass paste 76 is filled-in, and thereafter, the steps thereafter are carried out. However, manufacturing is also possible by a method in which function portions at the peripheries of the piezoelectric elements 45 are first formed, and thereafter, the silicon substrate 72 is opened from the reverse surface and the pressure chambers 50 are formed.
Operation of the inkjet recording device 10, which is equipped with the inkjet recording head 32 which is manufactured as described above, will be described next.
First, when an electric signal instructing printing is sent to the inkjet recording device 10, one of the recording sheets P is picked-up from the stocker 24, and is conveyed by the conveying device 26.
On the other hand, at the inkjet recording unit 30, the ink 110 has already been injected-in (filled-in) in the ink pooling chamber 38 of the inkjet recording head 32 shown in
Then, while the recording sheet P is being conveyed, by ink droplets being selectively ejected from the plural nozzles 56, a portion of the image based on the image data is recorded on the recording sheet P. Namely, voltages are applied to predetermined piezoelectric elements 45 at predetermined times by the driving ICs 60, the vibrating plates 48 are flexurally deformed in the vertical direction (are vibrated with out-of-plane), pressure is applied to the ink 110 within the pressure chambers 50, and the ink 110 is ejected as ink droplets from predetermined nozzles 56. When the image based on the image data has been completely recorded on the recording sheet P in this way, the recording sheet P is discharged-out to the tray 25 by the sheet discharging belt 23. In this way, the printing processing (image recording) onto the recording sheet P is completed.
As a dry etching condition of the electrode films (high melting point metals) such as the upper electrodes 54 or the lower electrodes 52 or the like, the etching selection ratio thereof with the SiO2 film of the vibrating plate 48 is small (<0.1 to 0.3). Therefore, for example, even in cases of etching an electrode film of 300 nm, an SiO2 film of 1 μm is cut-in (removed) with over-etching of 30%.
Namely, due to this cutting-in by the etching, a thickness difference of 1 μm arises at the vibrating plate 48 between the region thereof beneath the lower electrode 52 and the other regions thereof. Further, due to the wafer in-plane dispersion of the etching characteristic, dispersion in the cutting-in of the vibrating plate 48 in the plane of the wafer arises, therefore, dispersion of greater than or equal to 1 μm arises in the thickness of the vibrating plate 48. Here, there are limits to optimizing the etching condition (i.e., to improving the selection ratio), accordingly it is extremely difficult to completely eliminate cutting-in of the SiO2 film of the vibrating plate 48.
In this way, the decrease in the rigidity of the vibrating plates 48 arises, and dispersion arises in the amount of displacement per bit of each piezoelectric body 46 due to dispersion in the rigidity of the vibrating plates 48, by the cutting-in of the SiO2 film of the vibrating plates 48. However, as shown in
Specifically, due to the cutting-in of a vibrating plate 104, the vibrating plate 104 becomes thin, the mechanical strength of the vibrating plate 104 decreases extremely and a piezoelectric element 108, which includes a piezoelectric body 106, breaks at the time of machining. Further, the decrease in the rigidity of the vibrating plate 104 gives rise to dispersion in the amounts of displacement of the piezoelectric elements 108, such that stable driving of the device markedly deteriorates.
Thus, in order to suppress the decrease in rigidity due to the cutting-in of the vibrating plate 104, cutting-in of the vibrating plate 104 must be suppressed at regions which are thought to affect the piezoelectric characteristic. Here, a thick-walled portion 104A of the vibrating plate 104, which is positioned beneath the lower electrode 100, is not cut-in at the time when the lower electrode 100 is etched. Therefore, cutting-in of the periphery of the piezoelectric body 106 must be suppressed in order to drive the device stably.
Therefore, in the present exemplary embodiment, as shown in
Further, the lower electrode 52 is of a size such that one end side along the longitudinal direction of the lower electrode 52 (the metal wire 87 side) reaches the peripheral wall (the silicon substrate 72) of the pressure chamber 50. Because the region which is cut-in at the time of etching is a region other than beneath the lower electrode 52, the vibrating plate 48 is of a size such that a thick-walled portion 48A of the vibrating plate 48 reaches a peripheral wall of the pressure chamber 50 (a portion of the thick-walled portion 48A of the vibrating plate 48 overlaps with the peripheral wall of the pressure chamber 50 when viewed from the top), and a decrease in the rigidity of the vibrating plate 48, which is needed for the characteristic of the piezoelectric element 45, is suppressed.
Note that the present exemplary embodiment is merely an example, the present invention is not limited in any way by these structures. For example, in the present exemplary embodiment, the lower electrode 52 is of a size such that one end portion of the lower electrode 52 along the longitudinal direction reaches the peripheral wall (the silicon substrate 72) of the pressure chamber 50. However, as shown in
Namely, a pair of wall portions, which faces each other, of the peripheral wall of the pressure chamber 50 are bridged by the thick-walled portion 48A of the vibrating plate 48. Therefore, the lower electrode 52 and the vibrating plate 48 are reliably held by peripheral wall of the pressure chamber 50.
Further, as shown in
On the other hand, in the present exemplary embodiment, when the piezoelectric element 45 is formed on the vibrating plate 48, as shown in
Therefore, in the present exemplary embodiment, as shown in
Further, in the inkjet recording head 32, the ink pooling chamber 38 is provided at the opposite side (the upper side) of the pressure chambers 50, with the vibrating plates 48 (the piezoelectric elements 45) therebetween. In other words, the vibrating plates 48 (the piezoelectric elements 45) are disposed between the ink pooling chamber 38 and the pressure chambers 50, and the ink pooling chamber 38 and the pressure chambers 50 do not exist in the same horizontal plane.
Moreover, by providing isolating chambers 112 within the ink pooling chamber 38 and isolating the piezoelectric elements 45 from the ink 110 by the isolating chambers 112, constraining force due to the ink 110 is not applied to the piezoelectric elements 45.
On the other hand, when the pressure chamber 50 is pressurized due to the flexural deformation of the piezoelectric element 45 and the ink 110 is ejected as an ink droplet from the nozzle 56 connected to the pressure chamber 50, the pressure wave of the ink 110, which is transferred to the interior of the ink pooling chamber 38 via the ink flow path 66, is mitigated by the air damper 44 which is provided at the isolating chamber 112.
In the inkjet recording device 10 of the above-described exemplary embodiments, ink droplets are selectively ejected, on the basis of image data, from the inkjet recording units 30 of the respective colors of black, yellow, magenta, and cyan, such that a full-color image is recorded on the recording sheet P. However, the inkjet recording in the present invention is not limited to the recording of characters and images onto the recording sheet P.
Namely, the recording medium is not limited to paper, and the liquid which is ejected is not limited to ink. For example, the inkjet recording head 32 relating to the present invention can be applied to liquid droplet jetting devices in general which are used industrially, such as in fabricating color filters for displays by ejecting ink onto a high polymer film or glass, or in forming bumps for parts mounting by ejecting solder in a welded state onto a substrate, or the like.
Further, in the inkjet recording device 10 of the above-described exemplary embodiments, the example of a so-called Full Width Array (FWA), corresponding to the width of a sheet, is described. However, the present invention is not limited to the same, and may be a Partial Width Array (PWA) including a main scanning mechanism and a subscanning mechanism.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-342339 | Dec 2006 | JP | national |
