This application claims priority from Japanese Patent Application No. 2014-264177 filed on Dec. 26, 2014, which is incorporated herein by reference in its entirety.
1. Technical Field
The present disclosure relates to a liquid ejection apparatus.
2. Description of the Related Art
Japanese Patent No. 4811598 discloses an inkjet head as a liquid ejection apparatus. The inkjet head includes piezoelectric elements for ejection of a liquid. The inkjet head includes a channel defining substrate, which has a plurality of pressure chambers, and piezoelectric elements disposed for the corresponding pressure chambers of the channel defining substrate. The piezoelectric elements each include a piezoelectric film, a lower electrode film disposed below the piezoelectric film, and an upper electrode film disposed above the piezoelectric film. The lower electrode film is a common electrode for the piezoelectric elements. The upper electrode film is an individual electrode and is disposed for each of the piezoelectric elements. The lower electrode film includes a conductor layer mainly composed of platinum.
The thickness of the electrode is desired to be as thin as possible to reduce the cost if the electrode disposed below the piezoelectric film is made of platinum, which is expensive. In addition, the electrode having a large thickness may inhibit deformation of the piezoelectric film. However, reduction in the thickness of the electrode to overcome these problems increases the electrical resistance of the electrode, which adversely affects the behaviors (such as responsiveness) of the piezoelectric elements.
It is an object of the present disclosure to reduce the thickness of the electrode made of platinum to achieve a low cost and to reduce the substantial electrical resistance of the electrode.
According to an aspect of the disclosure, a liquid ejection apparatus includes a pressure chamber; a diaphragm covering the pressure chamber; a piezoelectric element having a piezoelectric component positioned opposing the pressure chamber; a first electrode disposed on a first side of the piezoelectric component toward the pressure chamber; a second electrode disposed on a second side of the piezoelectric component opposite the first side in an opposed region, the opposed region being a region opposed to the second electrode; and a metal film disposed between the piezoelectric component and the diaphragm, the metal film being absent from at least a portion of the opposed region. The metal film and the first electrode are in electrical contact with each other. The first electrode is made of platinum and the metal film is made of a metal material other than platinum.
According to a further aspect of the disclosure, a method of forming a liquid ejection apparatus is disclosed. The method includes forming a diaphragm layer on a surface of a substrate; forming a metal film in a first region; and forming a first electrode in the first region and in a second region, the first electrode layer being made of platinum and electrically contacting the metal film. The method also includes forming a piezoelectric layer over the first electrode layer; and forming a second electrode over the piezoelectric layer in the second region. The metal film is absent from at least a portion of the second region, and is made of a metal material other than platinum.
An embodiment of the present disclosure is described below.
As illustrated in
A recording sheet 100 as a recording medium is placed on an upper surface of the platen 2. The carriage 3 is configured to be reciprocated in a left-right direction, which may be referred to as a scanning direction hereinafter, along two guide rails 10 and 11 in an area facing the platen 2. An endless belt 14 connected to the carriage 3 is rotated by a carriage drive motor 15 to move the carriage 3 in the scanning direction.
The inkjet head 4 is mounted on the carriage 3 so as to be moved in the scanning direction together with the carriage 3. The inkjet head 4 includes four head units 16 arranged in the scanning direction. The head units 16 are each connected, through a tube (not illustrated), to a cartridge holder 7 that holds ink cartridges 17 of four colors (black, yellow, cyan, and magenta). Each head unit 16 includes a plurality of nozzles 24 (see
The transport mechanism 5 includes two transport rollers 18 and 19 disposed in the front-rear direction with the platen 2 being disposed therebetween. The transport mechanism 5 transports the recording sheet 100 on the platen 2 to the front (in a transport direction) by the transport rollers 18 and 19.
The controller 6 includes a Read Only Memory (ROM), a Random Access Memory (RAM), and an Application Specific Integrated Circuit (ASIC) including various control circuits, for example. The controller 6 directs the ASIC to execute various operations such as a printing operation on the recording medium 100 in accordance with a program in the ROM. In the printing operation, for example, the controller 6 controls the inkjet head 4, the carriage drive motor 15, and other components to print an image on the recording medium 100 based on a printing instruction input by an external device such as a PC. Specifically, the printing is performed by alternately repeating an ink ejection operation in which the inkjet head 4 ejects the ink while being moved in the scanning direction together with the carriage 3 and a transport operation in which the transport rollers 18 and 19 transport the recording sheet 100 a predetermined distance in the transport direction.
The inkjet head 4 is described in detail.
As illustrated in
The channel substrate 20 is a monocrystalline silicon substrate. The channel substrate 20 includes a plurality of pressure chambers 26. As illustrated in
The nozzle plate 21 is bonded to a lower surface of the channel substrate 20. The nozzle plate 21 includes a plurality of nozzles 24 that are in communication with the pressure chambers 26 of the channel substrate 20. As illustrated in
The piezoelectric actuator 22 is configured to apply ejection energy to the ink in the pressure chambers 26 so as to allow the ink to be ejected through the nozzles 24. The piezoelectric actuator 22 is disposed on an upper surface of the diaphragm 30 of the channel substrate 20. As illustrated in
Hereinafter, the piezoelectric elements 39 of the piezoelectric actuator 22 and other associated components are sequentially described. Each piezoelectric element 39 includes a piezoelectric portion 37, a lower electrode 31 disposed on a lower surface (surface adjacent to the diaphragm 30) of the piezoelectric portion 37, and an upper electrode 33 disposed on an upper surface (surface remote from the diaphragm 30) of the piezoelectric portion 37.
The lower electrode 31 is disposed on an upper surface of the diaphragm 30 so as to be positioned over the pressure chambers 26 corresponding to the piezoelectric elements 39. Specifically, as illustrated in
In this embodiment, as illustrated in
As illustrated in
The piezoelectric components 32 each have a rectangular shape elongated in the transport direction in plan view. Each piezoelectric component 32 has drive portions, which apply pressures to the pressure chambers 26, at positions facing the pressure chambers 26. The drive portions are referred to as piezoelectric portions 37. In other words, the piezoelectric portions 37 arranged in the transport direction are connected to constitute one piezoelectric component 32. Each piezoelectric component 32 is stacked on the lower electrode 31 so as to extend across the pressure chambers 26 in one of the pressure chamber rows. The lower electrode 31 is disposed on the lower surface (adjacent to the diaphragm 30) of the piezoelectric component 32. Each piezoelectric component 32 is made of a piezoelectric material including lead zirconate titanate (PZT) as a main component, for example. The lead zirconate titanate is a mixed crystal including lead titanate and lead zirconate. Alternatively, the piezoelectric component 32 may be made of a lead-free piezoelectric material.
The upper electrodes 33 are disposed on the upper surfaces of the piezoelectric components 32 in the regions opposed to the pressure chambers 26. The upper electrodes 33 are individual electrodes and are disposed on the corresponding piezoelectric elements 39. The shape of each upper electrode 33 is not particularly limited, but may be a rectangular shape that is smaller than the pressure chamber 26 in plan view as illustrated in
The piezoelectric portions 37 sandwiched between the lower electrode 31 and the upper electrodes 33 are polarized in the thickness direction toward a lower side, i.e., from the upper electrodes 33 to the lower electrode 31.
As illustrated in
The trace 35 extends from the corresponding piezoelectric element 39 in the scanning direction parallel to the surface of the diaphragm 30. Specifically, as illustrated in
Four traces 36 including two left and two right traces 36 are connected to the lower electrode 31. The two left traces 36 and the two right traces 36 extend from the lower electrode 31 to the left and to the right, respectively. One end of each trace 36 includes a ground contact 41. The ground contacts 41 and the driving contacts 40 form one line on each of the left and right end sections of the channel substrate 20 (diaphragm 30).
As illustrated in
A driver IC 51 is mounted on each COF 50. The driver IC 51 generates and outputs driving signals for driving the piezoelectric actuator 22 based on a control signal from the controller 6. The driving signals output by the driver IC 51 are received by the driving contacts 40 through the traces 55 of the COF 50 and supplied to the upper electrodes 33 through the traces 35 of the piezoelectric actuator 22. The upper electrodes 33 that have received the driving signals change in potential from the ground potential to a predetermined potential. The COF 50 further has ground traces (not illustrated) that are electrically connected to the ground contact 41 of the piezoelectric actuator 22. This configuration enables the potential of the lower electrode 31 connected to the ground contact 41 to be maintained at the ground potential.
The piezoelectric actuator 22 that has received the driving signal from the driver IC 51 operates as follows. Before the reception of the driving signal, the potential of each of the upper electrodes 33 is a ground potential, which is the same potential as the lower electrode 31. When the upper electrode 33 in such a state receives the driving signal, the potential thereof is changed to the driving potential. A potential difference between the upper electrode 33 and the lower electrode 31 generates parallel electric fields extending in the thickness direction of the piezoelectric portion 37. Since the direction of polarization of the piezoelectric portion 37 and the direction of the electric field are equal, the piezoelectric portion 37 elongates in the thickness direction, which is the direction of the polarization, and contracts in the planar direction. Due to such contraction deformation of the piezoelectric portion 37, the diaphragm 30 protrudes toward the pressure chamber 26. With this configuration, the volume of the pressure chamber 26 is reduced and a pressure wave is generated in the pressure chamber 26, which allows ink droplets to be ejected through the nozzle 24 in communication with the pressure chamber 26.
In this embodiment, the lower electrode 31 as the common electrode is made of platinum, which is expensive. The thickness of the lower electrode 31 is desired to be as small as possible to reduce cost. In addition, the deformation of the piezoelectric portion 37 is more likely to be inhibited as the thickness of the lower electrode 31 increases, and thus the lower electrode 31 is desired to have a small thickness. However, the reduction in the thickness of the lower electrode 31 increases the electrical resistance of the common electrode, which adversely affects the behavior of each piezoelectric element 39. The amount of the voltage drop between the ground contact 41 and the lower electrode 31 differs depending on the distance between the ground contact 41 and the piezoelectric element 39, for example. In the piezoelectric element 39 remote from the ground contact 41, the potential of the lower electrode 31 is likely to vary and become unstable, which adversely affects ejection properties such as responsiveness.
To solve such a problem, as illustrated in
As illustrated in
The configuration in which the metal films 38 are in direct contact with the lower electrode 31 enables the lower electrode 31 made of platinum to have a reduced thickness and to have a reduced substantial electrical resistance. The thickness of the lower electrode 31 may be reduced to 0.1 μm or smaller (preferably, 0.05 μm or less), for example. In addition, since the metal films 38 does not face the upper electrodes 33 (piezoelectric portions 37), the deformation of the piezoelectric portions 37 are unlikely to be inhibited by the metal films 38 stacked on the lower electrode 31. In the embodiment, since the entire area of the metal films 38 is in contact with the lower electrode 31, the substantial electrical resistance of the lower electrode 31 is largely reduced.
As illustrated in
As illustrated in
In the production of the piezoelectric actuator 22, various thermal processes such as annealing of a piezoelectric material film are performed as described above. One reason why the lower electrode 31 is made of platinum is that the metal atoms constituting the lower electrode 31 are unlikely to be dispersed into the piezoelectric portion 37 during a thermal process such as annealing of the piezoelectric portion 37. This is one of the reasons why the lower electrode 31 is made of platinum. However, if the metal film 38 made of the material other than platinum is stacked on the lower electrode 31 made of platinum and the piezoelectric portion 37 is disposed on the metal film 38, the metal constituting the metal film 38 is likely to be dispersed into the piezoelectric portion 37. If the metal of the metal film 38 is dispersed into the piezoelectric portion 37, the piezoelectric portion 37 has different phases, which may cause defects such as electrical breakdown. To prevent such defects, the metal film 38 in the embodiment is disposed adjacent to the channel substrate 20, i.e., on the opposite side of the lower electrode 31 from the piezoelectric portion 37. This configuration reduces the dispersion of the metal of the metal film 38 into the piezoelectric portion 37.
The metal film 38 may be made of any material other than platinum. The metal film 38 is preferably made of a metal material such as copper (Cu) and aluminum (Al) which has a low electric resistivity in view of reduction in the electrical resistance of the lower electrode 31. The metal film 38 is heated together with the piezoelectric portion 37 during the thermal process such as annealing of the piezoelectric portion 37. In view of this, the metal film 38 is preferably made of a metal material such as zirconium, tantalum, and tungsten, which has a high melting point.
As illustrated in
As illustrated in
A lower half portion of the reservoir defining member 23 includes a plurality of ink supply channels 53 extending downward from the reservoirs 52. Each ink supply channel 53 is in communication with the communication hole 30a in the diaphragm 30. This configuration allows the ink to be supplied from the reservoir 52 to the pressure chambers 26 in the channel substrate 20 through the ink supply channels 53 and the communication holes 30a. The lower half portion of the reservoir defining member 23 further includes a protective cover portion 54 covering the piezoelectric elements 39 of the piezoelectric actuator 22. The protective cover portion 54 does not include a wall at an opposite side (right side in
Next, steps of producing the inkjet head 4, particularly steps of producing the piezoelectric actuator 22 are described with reference to
In the embodiment, a film formation process such as sputtering and a patterning process such as etching are repeatedly performed to sequentially form various films on the diaphragm 30 of the channel substrate 20. As a result, the piezoelectric actuator 22 including the piezoelectric elements 39 is produced. As illustrated in
Then, as illustrated in
As illustrated in
In the above-described embodiment, the inkjet head 4 corresponds to the “liquid ejection apparatus” of the present disclosure. The lower electrode 31 and the upper electrode 33 correspond to the “first electrode” and the “second electrode” in the present disclosure respectively.
Next, various modifications of the above-described embodiment are described. Components in the modifications identical to those in the embodiment are assigned reference numerals the same as those in the embodiment and are not described in detail.
In the embodiment illustrated in
In the embodiment, the entire area of each metal film 38 is in direct contact with the lower electrode 31. However, as illustrated in
In the embodiment, the metal film 38 stacked on the lower electrode 31 has a thickness greater than that of the lower electrode 31. However, the metal film 38 may have a thickness equal to or smaller than that of the lower electrode 31.
In the embodiment, the piezoelectric portions 37 of the piezoelectric elements 39 arranged in a nozzle arrangement direction in which the nozzles are arranged (transport direction) are connected to form one piezoelectric component 32 as illustrated in
In the embodiment, the metal films 38 are separately disposed in non-opposed regions of the lower electrode 31, which are defined as being outside regions opposed to the upper electrodes 33 and positioned between the upper electrodes 33, as illustrated in
In the embodiment, as illustrated in
In the piezoelectric actuator 22 in the embodiment, the lower electrode 31 is the common electrode for the piezoelectric elements 39 and each upper electrode 33 is the individual electrode for each of the piezoelectric elements 39. However, the technique in the present disclosure may be applied to an opposite electrode configuration in which the piezoelectric element has the lower electrode as the individual electrode and the upper electrode as the common electrode.
The following is an example of the configuration including lower electrodes as the individual electrodes and an upper electrode as the common electrode.
The head unit 56 includes a channel substrate 60, a nozzle plate 61, a piezoelectric actuator 62, and a reservoir defining member 63. The configurations of the channel substrate 60, the nozzle plate 61, and the reservoir defining member 63 are substantially identical to those disclosed in the embodiment and are not described. Hereinafter, the configuration of the piezoelectric actuator 62 is mainly described.
As illustrated in
The trace layers 71a corresponding to the piezoelectric elements 79 in the second piezoelectric element row 85b on the left extend between the piezoelectric elements 79 (lower electrodes 71) in the first piezoelectric element row 85a to the right. Portions between adjacent two of the piezoelectric elements 79 (piezoelectric portions 77) of the piezoelectric component 72 extending in the transport direction over the pressure chambers 66 are eliminated by dry etching to form openings 72a. The openings 72a between adjacent two of the piezoelectric elements 79 of the piezoelectric component 72 accelerate the deformation of the piezoelectric portions 77 of the piezoelectric elements 79.
Each lower electrode 71 includes a right end portion including the trace layer 71a. The right end portion does not face the upper electrode 73. The metal film 78 made of a material other than platinum is disposed in the non-opposed regions of the lower electrodes 71. In
In this configuration, each metal film 78 includes trace layers 78a disposed over the trace layers 71a connected to the lower electrodes 71 in addition to the portions disposed over the lower electrodes 71. Each trace layer 78a extends to the driving contact 80 along the trace layer 71a made of platinum. The trace layer 71a made of platinum and the trace layer 78a of the metal film 78 constitutes a trace 75 for each piezoelectric element 79. This configuration reduces the electrical resistance of the traces 75 for the piezoelectric elements 79.
As illustrated in
In the configuration illustrated in
In the above-described embodiment and the modifications, the technique in the present disclosure is applied to the piezoelectric actuator of the inkjet head, which ejects ink to the recording medium to print an image, for example. However, the technique in the present disclosure may be applied to any liquid ejection apparatus that is used for any different usages than the printing of the image. The technique in the present disclosure may be applied to a liquid ejection apparatus that ejects a conductive liquid to a board to form a conductive pattern on the substrate, for example.
Number | Date | Country | Kind |
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2014-264177 | Dec 2014 | JP | national |