JP2006173249A - Piezoelectric actuator, its manufacturing process, and liquid ejection head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deformation of a supporting substrate by reducing film stress of a piezoelectric being deposited on the electrode of the supporting substrate. <P>SOLUTION: The piezoelectric actuator 60 is constituted by depositing a PZT film 68 having a thickness of 10 μm on the electrode 64 of a diaphragm 62 having a thickness of 10-20 μm by aerosol deposition (AD method), and a PZT film 66 having a thickness of ≥0.5 μm deposited by sputtering is interposed between the electrode 64 and the PZT film 68 of AD film. Since the PZT film 66 of sputtered film is composed of a material having composition identical to that of the PZT film 68 of AD film, compressive stress is not stored on the interface to the PZT film 68, and film stress of the PZT film 68 can be reduced. Since the PZT film 66 functions as a stress relax layer and exhibits low film stress and strong film adhesion, it also functions as a layer for enhancing adhesion of the PZT film 68 of AD film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a piezoelectric actuator, a method for manufacturing the same, and a liquid discharge head, and more particularly to a technique for reducing a film stress generated during film formation of a piezoelectric body.

  Conventionally, as a method for manufacturing an inkjet head, a method in which a bulk abrasive product of a piezoelectric body or a green sheet sintered body is attached to a vibration plate with an adhesive has been the mainstream, and there is no need to consider the film stress of the piezoelectric body.

  Also, in the method of manufacturing an ink jet head described in Patent Document 1, a piezoelectric film is epitaxially grown on an epitaxial substrate, a silicon substrate is directly bonded to the opposite side of the piezoelectric film, and then the epitaxial substrate is peeled off from the piezoelectric film. I have to. In this case, the film stress generated at the interface between the piezoelectric film and the epitaxial substrate after the piezoelectric film is formed can be removed by removing the epitaxial substrate.

  Furthermore, recently, with the increase in definition of inkjet heads, the piezoelectric body also needs to be a thin film, and there are some cases where the piezoelectric body is formed on the diaphragm by sputtering.

  On the other hand, in recent years, in the field of micro electrical mechanical systems (MEMS), sensors and actuators using piezoelectric ceramics are further integrated, and these elements are fabricated by film formation for practical use. Is being considered. As one of them, an aerosol deposition method (hereinafter referred to as “AD method”), which is known as a film forming technique for ceramics and metals, has attracted attention.

  The AD method is a method of forming a film by generating an aerosol from raw material powder, injecting the aerosol onto a substrate, and depositing the powder by collision energy at that time.

In manufacturing a liquid discharge head such as an ink jet head, it has been proposed to form a piezoelectric body or the like by the AD method (Patent Document 2).
JP 2003-309299 A JP 2003-136714 A

  By the way, since the film thickness of the piezoelectric material formed on the diaphragm by sputtering is about 3 μm and the film thickness is thin, even if film stress exists, it does not lead to significant deformation of the diaphragm. Stress control was not particularly important.

  On the other hand, when a piezoelectric material or the like is formed by the AD method as described in Patent Document 2, the AD film having a dense structure has a strong compressive stress, and when the film is formed on a thin diaphragm having a thickness of 30 μm or less, the diaphragm is The problem of stress deformation arises. Further, when the thickness of the piezoelectric body is 1 μm or more, and further about 10 μm, the deformation due to the film stress is more remarkable.

  9 is a graph showing the relationship between the thickness of the diaphragm (substrate) and the amount of stress deformation, and FIG. 10 is a graph showing the relationship between the thickness of the PZT piezoelectric film and the amount of stress deformation.

  Here, the amount of stress deformation shown in FIG. 9 is that a PZT piezoelectric film having a thickness of 10 μm is formed by AD method on a plurality of substrates having different thicknesses, and a strip-shaped structure having a length of 10 mm due to the film stress at this time. The deformation amount (height displacement amount at both ends) due to the warp of the object is shown. Further, the stress deformation amount shown in FIG. 10 is that the PZT piezoelectric films having different thicknesses are formed on the substrate having a thickness of 30 μm by the AD method, and the warpage of the strip-shaped structure having a length of 10 mm due to the film stress at this time. The deformation amount due to is shown.

  FIG. 11A shows an ideal form in which the piezoelectric body 2 formed on the diaphragm 1 has no film stress and the diaphragm 1 is not deformed, and FIG. This shows a form in which stress acts and the diaphragm 1 undergoes stress deformation in an uneven shape.

  When stress deformation occurs in the diaphragm 1 as shown in FIG.

  (1) A gap is generated when the vibration plate 1 and the ink chamber partition 3 are bonded, resulting in the following problems.

  a) The ink chamber 4 cannot be separated by the ink chamber partition wall 3, and the ink moves between the ink chambers 4 adjacent to each other or accumulates in the gap, and the amount of ink ejected from the nozzle becomes uncontrollable.

  b) A portion in which the vibration plate 1 is not fixed to the ink chamber partition wall 3 is generated, the in-plane displacement volume and torque vary, and an image defect due to in-plane ink ejection unevenness occurs.

  c) Adhesive fixation between the diaphragm 1 and the ink chamber partition wall 3 cannot be reliably performed, and durability over time cannot be guaranteed.

  (2) The deformation of the diaphragm 1 causes the capacity of the ink chamber 4 to change, and even if the diaphragm 1 is driven with the same displacement volume, the amount of ejected ink varies, resulting in uneven ink ejection within the surface. An image defect occurs.

  (3) When the vibration plate 1 is deformed, a wiring defect occurs without achieving an alignment accuracy such as a wiring process to an electrode for driving the piezoelectric body 2 thereafter.

  The present invention has been made in view of such circumstances, and a piezoelectric actuator capable of reducing the film stress of the piezoelectric body formed on the electrode of the support substrate and suppressing the deformation of the support substrate, and a method for manufacturing the same. An object of the present invention is to provide a liquid discharge head.

  In order to achieve the above object, a piezoelectric actuator according to claim 1 includes a support substrate, an electrode formed on the support substrate, a stress relaxation layer formed on the electrode, and a stress relaxation layer. It is characterized in that a film stress at the time of film formation of the piezoelectric body is reduced by the stress relaxation layer.

  When no stress relaxation layer is interposed between the electrode on the support substrate and the piezoelectric body, a film stress (compressive stress) accompanying the film formation of the piezoelectric body acts on the interface between the piezoelectric body and the electrode. However, by interposing the stress relaxation layer, the film stress of the piezoelectric body is reduced to suppress deformation of the support substrate.

  According to a second aspect of the present invention, in the piezoelectric actuator according to the first aspect, the piezoelectric body is formed on the stress relaxation layer by an aerosol deposition method. The aerosol deposition method can form a thick film that cannot be formed by sputtering, but the piezoelectric film formed by the aerosol deposition method has a dense structure and a strong film stress in the compression direction. work. The stress relaxation layer has a function of reducing the generation of the film stress.

  According to a third aspect of the present invention, in the piezoelectric actuator according to the first or second aspect, the stress relaxation layer is formed on the electrode by a film forming method in which film stress is not generated or film stress is reduced. It is characterized by that. This is to prevent stress from being generated at the interface between the electrode and the stress relaxation layer when the stress relaxation layer is formed.

  4. The piezoelectric actuator according to claim 1, wherein the stress relaxation layer is one of a sputtering method, a sol-gel method using hydrolysis, and an organometallic decomposition method using thermal decomposition. It is characterized by being formed on the electrode by the film forming method.

  According to a fifth aspect of the present invention, in the piezoelectric actuator according to the second aspect, the stress relaxation layer is a low-density film formed on the electrode by an aerosol deposition method and having a density lower than the film density of the piezoelectric body. It is characterized by being. When the stress relaxation layer is formed by the aerosol deposition method, the density is controlled by controlling the raw material powder conditions and film formation conditions, and the stress relaxation layer itself is greatly reduced by making the stress relaxation layer a low-density film. Film stress is not generated.

  According to a sixth aspect of the present invention, in the piezoelectric actuator according to the fifth aspect, the stress relaxation layer is a low-density film having a Vickers hardness of 600 Hv or less. Note that there is a correlation between the density and the Vickers hardness.

  According to a seventh aspect of the present invention, in the piezoelectric actuator according to any one of the first to third aspects, the stress relaxation layer is made of a composition material equivalent to that of the piezoelectric body. By using a stress relaxation layer having a composition material equivalent to that of the piezoelectric body, it is possible to prevent compressive stress from accumulating at the interface between the stress relaxation layer and the piezoelectric body, and to contribute to piezoelectric driving.

  According to an eighth aspect of the present invention, in the piezoelectric actuator according to any one of the first to sixth aspects, the stress relaxation layer is made of a high dielectric constant material. If the stress relaxation layer is made of a high dielectric constant material, the electric field loss is small and the displacement operation is not lost.

  According to a ninth aspect of the present invention, in the piezoelectric actuator according to any one of the first to eighth aspects, the stress relaxation layer includes a plurality of layers, and each layer is different in at least one of a film forming method and a material. .

  According to a tenth aspect of the present invention, in the piezoelectric actuator according to any one of the first to ninth aspects, the thickness of the support substrate is 30 μm or less.

  According to an eleventh aspect of the present invention, in the piezoelectric actuator according to any one of the first to tenth aspects, the thickness of the piezoelectric body is 1 μm or more.

  That is, a piezoelectric actuator for realizing a high-definition and high-torque piezoelectric inkjet head has a thickness of 1 μm or more (preferably about 10 μm) on a thin support substrate (vibration plate) having a thickness of 30 μm or less (preferably about 15 μm). It is important to directly form a thick piezoelectric film.

  The piezoelectric actuator according to any one of claims 1 to 11, wherein the piezoelectric body formed on the stress relaxation layer is a PZT film, and the crystal a-axis length of the PZT film is 2.025 to It is characterized by a range of 2.040 angstroms. When the crystal a-axis length of the PZT film is in the range of 2.025 to 2.040 angstroms, the film stress of the PZT film does not greatly deform the support substrate.

  A liquid discharge head according to a thirteenth aspect is the pressure chamber filled with the liquid, the nozzle for discharging the liquid from the pressure chamber, and the piezoelectric actuator according to any one of the first to twelfth aspects, The support substrate includes a piezoelectric actuator that is a vibration plate for changing the volume in the pressure chamber and discharging liquid from the nozzle. This liquid discharge head can achieve high definition and high torque.

  The piezoelectric actuator manufacturing method according to claim 14 is a stress relaxation layer forming step of forming one or more stress relaxation layers by a film formation method in which film stress is not generated on the electrodes of the support substrate or film stress is reduced. And a piezoelectric film forming step of forming a piezoelectric film by injecting an aerosol containing a piezoelectric raw material powder onto the stress relaxation layer by an aerosol deposition method and depositing the powder on the stress relaxation layer. The stress relaxation layer is made of a material that reduces film stress generated at the interface with the piezoelectric film.

  According to the present invention, since the stress relaxation layer is formed between the electrode of the support substrate and the piezoelectric body directly formed on the electrode, the film stress of the piezoelectric body formed on the electrode is reduced. This can be reduced, whereby the deformation of the support substrate can be suppressed.

  DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a piezoelectric actuator, a manufacturing method thereof, and a liquid discharge head according to the present invention will be described in detail below with reference to the accompanying drawings.

[Outline of inkjet recording apparatus]
First, an outline of an ink jet recording apparatus to which a liquid discharge head according to the present invention is applied will be described.

  FIG. 1 is an overall configuration diagram of an ink jet recording apparatus. As shown in the figure, the inkjet recording apparatus 10 includes a printing unit 12 having a plurality of liquid ejection heads (hereinafter simply referred to as “heads”) 12K, 12C, 12M, and 12Y provided for each color of ink. An ink storage / loading unit 14 that stores ink to be supplied to each of the heads 12K, 12C, 12M, and 12Y, a paper feeding unit 18 that supplies the recording paper 16, and a decurling unit 20 that removes curl from the recording paper 16. A suction belt conveyance unit 22 that is disposed opposite to the nozzle surface (ink ejection surface) of the printing unit 12 and conveys the recording paper 16 while maintaining the flatness of the recording paper 16, and a printing result by the printing unit 12 And a paper discharge unit 26 that discharges printed recording paper (printed matter) to the outside.

  The recording paper 16 delivered from the paper supply unit 18 retains curl due to having been loaded in the magazine. In order to remove this curl, heat is applied to the recording paper 16 by the heating drum 30 in the direction opposite to the curl direction of the magazine in the decurling unit 20.

  In the case of an apparatus configuration that uses roll paper, a cutter (first cutter) 28 is provided as shown in FIG. 1, and the roll paper is cut into a desired size by the cutter 28. The cutter 28 includes a fixed blade 28A having a length equal to or greater than the conveyance path width of the recording paper 16, and a round blade 28B that moves along the fixed blade 28A. The fixed blade 28A is provided on the back side of the print. The round blade 28B is disposed on the printing surface side with the conveyance path interposed therebetween. Note that the cutter 28 is not necessary when cut paper is used.

  After the decurling process, the cut recording paper 16 is sent to the suction belt conveyance unit 22. The suction belt conveyance unit 22 has a structure in which an endless belt 33 is wound between rollers 31 and 32, and at least portions facing the nozzle surface of the printing unit 12 and the sensor surface of the printing detection unit 24 are horizontal ( Flat surface).

  The belt 33 has a width that is greater than the width of the recording paper 16, and a plurality of suction holes (not shown) are formed on the belt surface. As shown in FIG. 1, a suction chamber 34 is provided at a position facing the nozzle surface of the print unit 12 and the sensor surface of the print detection unit 24 inside the belt 33 spanned between the rollers 31 and 32. Then, the suction chamber 34 is sucked by the fan 35 to be a negative pressure, whereby the recording paper 16 on the belt 33 is sucked and held.

  The power of a motor (not shown) is transmitted to at least one of the rollers 31 and 32 around which the belt 33 is wound, so that the belt 33 is driven in the clockwise direction in FIG. The recording paper 16 is conveyed from left to right in FIG.

  Since ink adheres to the belt 33 when a borderless print or the like is printed, the belt cleaning unit 36 is provided at a predetermined position outside the belt 33 (an appropriate position other than the print area).

  A heating fan 40 is provided on the upstream side of the printing unit 12 on the paper conveyance path formed by the suction belt conveyance unit 22. The heating fan 40 heats the recording paper 16 by blowing heated air onto the recording paper 16 before printing. Heating the recording paper 16 immediately before printing makes it easier for the ink to dry after landing.

  The printing unit 12 is a so-called full line type head in which line type heads having a length corresponding to the maximum paper width are arranged in a direction (main scanning direction) orthogonal to the paper feed direction (see FIG. 2). As shown in FIG. 2, each of the print heads 12K, 12C, 12M, and 12Y has an ink discharge port (nozzle) over a length that exceeds at least one side of the maximum size recording paper 16 targeted by the inkjet recording apparatus 10. It is composed of a plurality of line type heads.

  Heads 12K, 12C, 12M, and 12Y corresponding to the respective color inks are arranged in the order of black (K), cyan (C), magenta (M), and yellow (Y) from the upstream side along the feeding direction of the recording paper 16. Yes. A color image can be formed on the recording paper 16 by ejecting the color inks from the heads 12K, 12C, 12M, and 12Y while conveying the recording paper 16, respectively.

  The print detection unit 24 includes a line sensor for imaging the droplet ejection result of the print unit 12, and functions as means for checking nozzle clogging and other ejection defects from the droplet ejection image read by the line sensor.

  A post-drying unit 42 is provided following the print detection unit 24. The post-drying unit 42 is means for drying the printed image surface, and for example, a heating fan is used. Since it is preferable to avoid contact with the printing surface until the ink after printing is dried, a method of blowing hot air is preferred.

  A heating / pressurizing unit 44 is provided following the post-drying unit 42. The heating / pressurizing unit 44 is a means for controlling the glossiness of the image surface, and pressurizes with a pressure roller 45 having a predetermined surface uneven shape while heating the image surface to transfer the uneven shape to the image surface. To do.

  The printed matter generated in this manner is cut into a predetermined size by the cutter 28 and then discharged from the paper discharge unit 26. It is preferable that the original image to be printed (printed target image) and the test print are discharged separately. The ink jet recording apparatus 10 is provided with a sorting means (not shown) that switches the paper discharge path so as to select the print product of the main image and the print product of the test print and send them to the discharge units 26A and 26B. Yes. When the main image and the test print are simultaneously formed in parallel on a large sheet, the test print portion is cut off by the cutter (second cutter) 48.

[Film formation method by aerosol deposition method (hereinafter referred to as “AD method”)]
Next, a film forming method by the AD method used for manufacturing the piezoelectric actuator according to the present invention will be described.

  FIG. 3 is a schematic view showing a film forming apparatus using the AD method. This film forming apparatus has an aerosol generation container 52 in which raw material powder 51 is arranged. Here, the aerosol refers to solid or liquid fine particles suspended in a gas.

The aerosol generation container 52 is provided with a carrier gas introduction part 53, an aerosol lead-out part 54, and a vibration part 55. By introducing a gas such as nitrogen gas (N ₂ ) from the carrier gas introduction part 53, the raw material powder disposed in the aerosol generation container 52 is blown up to generate an aerosol. At that time, vibration is applied to the aerosol generation container 52 by the vibration unit 55, whereby the raw material powder is stirred and the aerosol is efficiently generated. The generated aerosol is guided to the film forming chamber 56 through the aerosol deriving unit 54.

  The film forming chamber 56 is provided with an exhaust pipe 57, a nozzle 58, and a movable stage 59. The exhaust pipe 57 is connected to a vacuum pump and exhausts the film forming chamber 56. The aerosol generated in the aerosol generation container 52 and guided to the film forming chamber 56 through the aerosol deriving unit 54 is ejected from the nozzle 58 toward the support substrate 50. Thereby, the raw material powder collides and accumulates on the support substrate 50. The support substrate 50 is placed on a movable stage 59 that can move in three dimensions. By controlling the movable stage 59, the relative position between the support substrate 50 and the nozzle 58 is adjusted.

[Target thickness of piezoelectric body and support substrate]
In order to realize a high-definition liquid discharge head, the size of the piezoelectric body is 300 μm square, and the size of the support substrate (vibration plate) is 500 μm square.

  FIG. 4A is a graph showing the relationship between the thickness of a piezoelectric body made of lead zirconate titanate (PZT), the displacement volume, and the generated pressure under the above conditions, and FIG. It is a graph which shows the relationship between thickness, displacement volume, and generated pressure.

  As shown in FIG. 4A, when the droplet size (volume target) of the liquid ejection head is x picoliter (pl) and the pressure target is y megapascal (Mpa), both the volume target and the pressure target are satisfied. The thickness of PZT is 10 μm.

  Similarly, as shown in FIG. 4B, when the volume target is x (pl) and the pressure target is y (Mpa), the thickness of the diaphragm that satisfies both the volume target and the pressure target is 15 μm.

  When depositing PZT directly on the diaphragm, the thickness that can be deposited by sputtering is about 3 μm. Therefore, to form a 10 μm PZT film as described above, film formation by AD is suitable. It is.

[Piezoelectric actuator structure]
As described above, when a PZT film having a thickness of 10 μm is formed on the vibration plate having a thickness of 15 μm by the AD method, the PZT film having a dense structure exerts a strong compressive stress on the PZT film itself. This compressive stress was higher at the interface with the diaphragm than within the film, and damage was confirmed on the diaphragm side by electron microscope observation of the interface with the diaphragm.

  For this reason, it is considered that the diaphragm is brought into a non-equilibrium state due to the high energy particles being driven into the diaphragm during AD film formation, and excessive energy is accumulated at the interface, which is the cause of the generation of film stress (compressive stress). It is done. Therefore, by reducing the damage at the interface of the diaphragm, the film stress of the PZT film is reduced (stress deformation of the diaphragm is suppressed).

(First embodiment)
FIG. 5 is a cross-sectional view of a principal part showing a first embodiment of the piezoelectric actuator according to the present invention. As shown in FIG. 5, in this piezoelectric actuator 60, an electrode 64 made of platinum (Pt) is formed by sputtering on a substrate (vibrating plate) 62 made of silicon (Si) or zirconia (ZrO2). A PZT film 66 is formed as a stress relaxation layer on the PZT film 66 by sputtering, and a PZT film 68 is formed on the PZT film 66 at room temperature by AD.

  The diaphragm 62 has a thickness of 10-20 μm, and the electrode 64 has a thickness of 500 nm. The thickness of the sputtered PZT film 66 is 0.5 μm or more, and the thickness of the AD PZT film 68 is 10 μm. Note that the upper limit of the thickness of the PZT film 66 of the sputtered film is a thickness that can be formed by a sputtering method, and is, for example, about 3 μm.

  When the PZT film 66 was formed on the electrode 64 by sputtering, no electrode damage was confirmed from the cross-sectional electron micrograph, and it was confirmed that the unevenness of the electrode 64 was 0.01 μm or less. Further, although the thickness of the PZT film 66 was 0.5 μm or more, no film stress deformation of the diaphragm 62 was confirmed.

  As a result of measuring the film stress deformation amount of the diaphragm 62, it was confirmed that the film stress of the 10 μm thick PZT film 68 formed on the PZT film 66 by AD was reduced to 10%. Also, film peeling was not confirmed in the film adhesion test, and it was confirmed that adhesion having no practical problem was secured.

(Second embodiment)
FIG. 6 is a cross-sectional view of an essential part showing a second embodiment of the piezoelectric actuator according to the present invention. In addition, the same code | symbol is attached | subjected to the part which is common in FIG. 5, and the detailed description is abbreviate | omitted.

  The piezoelectric actuator 70 of the second embodiment shown in FIG. 6 is different from the first embodiment shown in FIG. 5 in that two PZT films 66 and 72 are formed as stress relaxation layers.

  The PZT film 66 formed on the electrode 64 of the two layers of PZT films 66 and 72 is a sputtered film formed by the sputtering method as described above, and the PZT film 72 formed on the PZT film 66 is A low-density AD film formed at room temperature by the AD method.

  The low-density PZT film 72 is formed by AD film formation so as to reduce the density by controlling raw material powder conditions and film formation conditions. The low-density PZT film here has a Vickers hardness of 600 Hv or less. Refers to the membrane. The thickness of the PZT film 72 is 1 μm.

  On the low-density PZT film 72, a high-density PZT film 68 having a thickness of 10 μm is formed at room temperature by the AD method.

  Here, a method for controlling the density of the AD film will be described.

  As a result of investigating the relationship between the average particle diameter of the raw material PZT powder and the film quality of the AD film using SEM (scanning electron microscope), the larger the average particle diameter of the raw material PZT powder, the higher the average crystal in the AD film. The particle size is small and highly dense (the porosity is low). Conversely, the smaller the average particle size of the raw material PZT powder is, the larger the average crystal grain size in the AD film is, and the lower the density is (the porosity is lower). it was high).

  In addition, the average particle diameter of the raw material PZT powder and the Vickers hardness (Hv) of the AD film have a correlation. The larger the average particle diameter of the raw material PZT powder, the larger the Vickers hardness of the AD film. It was confirmed that the smaller the average particle size of the PZT powder, the smaller the Vickers hardness of the AD film.

  These observation results and measurement results are considered to be caused by the following mechanism. That is, the primary particles having a large particle diameter have a large kinetic energy when ejected from the nozzle, and thus are easily crushed when they collide with the substrate. For this reason, the fragmented primary particles are bonded to each other by a mechanochemical reaction, so that a dense and strong AD film is formed. On the other hand, primary particles having a small particle diameter have a small kinetic energy, so that they are not easily crushed even when they collide with a substrate. Even if such primary particles collide with the substrate, they are only trapped and deposited in the lower layer, so that the density is low (the porosity is high) and the film becomes relatively brittle.

  Therefore, by defining the average particle size of the raw material powder based on such a mechanism, it becomes possible to control the average crystal particle size, density (porosity) and hardness of the AD film.

  After forming the low-density PZT film 72 having a thickness of 1 μm and the high-density PZT film 68 having a thickness of 10 μm as described above, annealing was performed at 600 ° C. The annealing atmosphere was oxygen or air.

  When a low-density PZT film is formed directly on the electrode 64 without the stress relaxation layer of the PZT film 66 formed by the sputtered film, the effect of reducing the stress is confirmed, but the adhesion is poor by the film peeling test. Improvement of adhesion was a problem. Introducing a sputtered film as a stress relaxation layer and performing an annealing process that also improves characteristics not only confirms that the film stress has been reduced to about 5%, but also significantly improves film adhesion. It was confirmed that

  From the structural analysis of the film, it was found that the sputtered film and the low-density AD film were firmly bonded by particle growth, and strong adhesion was obtained. It was confirmed that by introducing two stress relaxation layers of a sputtered film and a low-density AD film, the stress was greatly reduced and the adhesion was sufficiently secured.

(Third embodiment)
FIG. 7 is a cross-sectional view of an essential part showing a third embodiment of the piezoelectric actuator according to the present invention. In addition, the same code | symbol is attached | subjected to the part which is common in FIG. 5, and the detailed description is abbreviate | omitted.

  The piezoelectric actuator 80 of the third embodiment shown in FIG. 7 is different from the sputtered PZT film 66 in that a sol-gel PZT film 82 is formed as a stress relaxation layer in the first embodiment shown in FIG. Different from the example.

  That is, a PZT film 82 is formed on the electrode 64 of the diaphragm 62 as a stress relaxation layer by a sol-gel method.

  The PZT film 82 by this sol-gel method is prepared by preparing a sol-gel solution having a PZT composition and applying it on the electrode 64 of the diaphragm 62 by spin coating, followed by drying (150 ° C.) and desolvation (400 ° C.). The film thickness is controlled by repeating, and finally, the film is formed by baking at 550 ° C.

  In the case of the PZT film 82 of the sol-gel film, no electrode damage was confirmed from the cross-sectional electron micrograph, and it was confirmed that the unevenness of the electrode 64 was 0.01 μm or less. Further, no film stress deformation of the diaphragm 62 was confirmed.

  The sol-gel method is a solution film-forming method by hydrolysis. Instead of the sol-gel method, a chemical solution is obtained by another chemical solution method such as an organometallic decomposition method (MOD method) which is a solution-forming method by thermal decomposition. A film may be formed.

  In the first to third embodiments, a sputtered PZT film 66 (first example), a sputtered PZT film 66 + a low-density AD film PZT film 72 (second example), and a sol-gel film are used. Since the PZT film 82 (third embodiment) of the chemical solution film is made of a material having the same composition as the PZT film 68 of the AD film, the compressive stress is not accumulated at the interface with the PZT film 68 and the film stress is increased. In the case of the sputtered film of the PZT film 66 and the chemical solution film of the PZT film 82, the film stress is low and the film adhesion is strong, so that the PZT film 68 of the AD film can be reduced. It can also have a function as an adhesion improving layer.

  Since the sputtered PZT film 66, the low-density AD film PZT film 72, the chemical solution film PZT film 82, and the AD film PZT film 68 are made of the same material, heat treatment (for example, residual stress is reduced). In order to remove it, an annealing process in which the temperature is kept at 600 ° C. for 1 hour is performed, so that particle fusion proceeds and chemical bonding occurs, resulting in stronger adhesion. Furthermore, since the PZT films 66, 72, and 82 contribute to the piezoelectric drive even if they are stress relaxation layers, the displacement operation of the piezoelectric actuator 60 is not lost.

Further, if the stress relaxation layer does not have the same composition as the piezoelectric film, if it is a high dielectric constant material, the electric field loss is small and the displacement operation loss of the piezoelectric actuator does not occur. Therefore, the stress relaxation layer may be a high dielectric constant material. Examples of the high dielectric constant material include SiO ₂ , alumina, hafnia (HfO 2), barium strontium titanate, niobium tantalum pentoxide, and the like.

  In addition, as shown in the second embodiment, the stress relaxation layer is not limited to a single layer, but may have a multilayer structure, and a method for forming each stress relaxation layer can be arbitrarily selected.

[Quantification of film stress]
In order to quantify the film stress of the AD film, the crystal a-axis length was evaluated by X-ray diffraction (XRD).

  First, in order to grasp the stress-free state, XRD evaluation of PZT fine particles as a raw material for the AD film was performed. As a result, the a-axis length was 2.034 angstroms (Å). Furthermore, when an XRD evaluation of a bulk sintered product obtained by sintering PZT fine particles at 1250 ° C. was performed, the a-axis length was 2.030 mm. Therefore, the a-axis length of PZT in a stress-free state is defined as about 2.025 to 2.040 mm. That is, the average value of 2.032 ± 0.007 mm of the a-axis length (2.034 mm) of the PZT fine particles and the a-axis length (2.030 mm) of the bulk sintered product was defined as PZT in a stress-free state. Here, the upper limit value and the lower limit value of 2.025 to 2.040 mm are values at which the deformation amount of the vibration plate becomes ± 10 μm due to the film stress of the PZT film, and 10 μm adheres the vibration plate to the ink chamber partition wall or the like. It is the thickness of the adhesive at the time.

  When the stress relaxation layer is not introduced, the PZT film a-axis length by the AD method (room temperature film formation) is 2.055 mm, and in the example in which the film stress is reduced to 10%, the a-axis length changes to 2.033 mm. It was confirmed that

[Liquid discharge head structure]
FIG. 8 is a cross-sectional view of an essential part of the liquid discharge head according to the present invention. In addition, the same code | symbol is attached | subjected to the part which is common in FIG. 5, and the detailed description is abbreviate | omitted.

  The liquid discharge head 90 shown in FIG. 8 is configured by attaching the piezoelectric actuator 60 and the pressure chamber partition 92 shown in FIG. 5 with an adhesive, and attaching a nozzle plate 94 to the lower surface of the pressure chamber partition 92. . An electrode 91 is formed on the upper surface of the PZT film 68.

  A liquid (ink) is supplied to a pressure chamber 98 defined by the pressure chamber partition via a liquid flow path (not shown), and the liquid discharge head 90 is 1 kV / mm between the electrodes 64 and 91. By applying a DC pulse electric field of a degree, the vibration plate 62 is driven to be displaced, and ink of a desired droplet size is ejected from the nozzle 96 formed on the nozzle plate 94.

  Although the piezoelectric actuator according to the present invention has been described as being applied as an actuator for a liquid ejection head, it can also be used as an actuator for other devices. Further, the liquid ejection head according to the present invention has been described as being used as a line-type inkjet head that ejects ink onto recording paper. However, the present invention is not limited to this, and the head reciprocates in a direction perpendicular to the feeding direction of the print medium. It can also be applied to a shuttle-type head that moves. Furthermore, the liquid discharge head according to the present invention is a liquid for forming an image recording medium as an image forming head by ejecting a treatment liquid or water onto a recording medium, and by ejecting a coating liquid onto a substrate. It may be used as a discharge head.

FIG. 1 is an overall configuration diagram of an ink jet recording apparatus according to the present invention. FIG. 2 is a plan view of the main part around the printing unit of the ink jet recording apparatus shown in FIG. FIG. 3 is a schematic view showing a film forming apparatus using the AD method. 4A is a graph showing the relationship between the thickness of a piezoelectric body made of lead zirconate titanate (PZT), the displacement volume, and the generated pressure, and FIG. 4B is the thickness, displacement volume, and generation of the diaphragm. It is a graph which shows the relationship with a pressure. FIG. 5 is a cross-sectional view of a principal part showing a first embodiment of the piezoelectric actuator according to the present invention. FIG. 6 is a cross-sectional view of an essential part showing a second embodiment of the piezoelectric actuator according to the present invention. FIG. 7 is a cross-sectional view of an essential part showing a third embodiment of the piezoelectric actuator according to the present invention. FIG. 8 is a cross-sectional view of an essential part of the liquid discharge head according to the present invention. FIG. 9 is a graph showing the relationship between the thickness of the diaphragm (substrate) and the amount of stress deformation. FIG. 10 is a graph showing the relationship between the thickness of the PZT piezoelectric film and the amount of stress deformation. FIG. 11A shows an ideal form in which the piezoelectric body formed on the diaphragm has no film stress and the diaphragm is not deformed, and FIG. 11B shows a compressive stress acting on the piezoelectric body. It is a figure which shows the form which stress-deforms in uneven | corrugated shape.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12 ... Printing part, 12K, 12C, 12M, 12Y ... Head, 60, 70, 80 ... Piezoelectric actuator, 62 ... Diaphragm, 64, 91 ... Electrode, 66 ... PZT film of sputtered film, 68 ... AD film PZT film, 72 ... low-density PZT film, 82 ... sol-gel film PZT film, 90 ... liquid ejection head, 92 ... pressure chamber partition, 94 ... nozzle plate, 96 ... nozzle, 98 ... pressure chamber

Claims (14)

A support substrate; an electrode formed on the support substrate; a stress relaxation layer formed on the electrode; and a piezoelectric body formed on the stress relaxation layer.
A piezoelectric actuator characterized in that a film stress during film formation of the piezoelectric body is reduced by the stress relaxation layer.   The piezoelectric actuator according to claim 1, wherein the piezoelectric body is formed on the stress relaxation layer by an aerosol deposition method.   3. The piezoelectric actuator according to claim 1, wherein the stress relaxation layer is formed on the electrode by a film forming method in which film stress is not generated or film stress is reduced.   The stress relaxation layer is formed on the electrode by any one of a sputtering method, a sol-gel method using hydrolysis, and an organometallic decomposition method using thermal decomposition. Item 3. The piezoelectric actuator according to Item 1 or 2.   3. The piezoelectric actuator according to claim 2, wherein the stress relaxation layer is a low-density film formed on the electrode by an aerosol deposition method and having a density lower than the film density of the piezoelectric body.   6. The piezoelectric actuator according to claim 5, wherein the stress relaxation layer is a low-density film having a Vickers hardness of 600 Hv or less.   The piezoelectric actuator according to claim 1, wherein the stress relaxation layer is made of a material having the same composition as or substantially the same composition as the piezoelectric body.   The piezoelectric actuator according to claim 1, wherein the stress relaxation layer is made of a high dielectric constant material.   The piezoelectric actuator according to any one of claims 1 to 8, wherein the stress relaxation layer includes a plurality of layers, and each layer is different in at least one of a film forming method and a material.   The piezoelectric actuator according to claim 1, wherein the support substrate has a thickness of 30 μm or less.   11. The piezoelectric actuator according to claim 1, wherein the piezoelectric body has a thickness of 1 μm or more.   The piezoelectric body formed on the stress relaxation layer is a PZT film, and a crystal a-axis length of the PZT film is in a range of 2.025 to 2.040 angstroms. Piezoelectric actuator. A pressure chamber filled with liquid;
A nozzle for discharging liquid from the pressure chamber;
The piezoelectric actuator according to any one of claims 1 to 12, wherein the support substrate is a vibration plate for changing the volume in the pressure chamber to discharge liquid from the nozzle;
A liquid discharge head comprising: A stress relaxation layer forming step of forming one or more stress relaxation layers by a film forming method in which film stress is not generated on the electrode of the support substrate or the film stress is reduced;
A piezoelectric film forming step of spraying an aerosol containing a piezoelectric raw material powder onto the stress relaxation layer by an aerosol deposition method and depositing the powder on the stress relaxation layer to form a piezoelectric film;
The method of manufacturing a piezoelectric actuator, wherein the stress relaxation layer is made of a material that reduces a film stress generated at an interface with the piezoelectric film.

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