JP4310672B2 - Piezoelectric element, ink jet recording head, and printer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric element used for an ink jet recording head or the like, and in particular, a piezoelectric element provided with a piezoelectric film that is less likely to cause current leakage and has good voltage resistance, and a piezoelectric element of such a piezoelectric film. The present invention relates to a manufacturing method capable of thickening.
[0002]
[Prior art]
A piezoelectric element is an element in which a piezoelectric film exhibiting an electromechanical conversion function is sandwiched between two electrodes, and the piezoelectric film is made of crystallized piezoelectric ceramics. As a method for manufacturing this piezoelectric element, a so-called sol-gel method is used, in which an organic metal sol is applied on the lower electrode, dried and degreased, and then subjected to high heat treatment for crystallization, and finally high heat is applied at a stretch. A method of crystallization is known. When a piezoelectric element is manufactured by this method, there is a problem in that internal stress acts along with crystallization, and a crack is easily generated in the piezoelectric thin film.
[0003]
On the other hand, there is also known a method in which an organic metal sol is applied on a lower electrode, dried and degreased, and then placed in a predetermined alkaline solution and crystallized at a constant temperature and a constant pressure. Such a method of crystallization in an alkaline aqueous solution is called a hydrothermal method. This hydrothermal method has a number of advantages because it can be crystallized at a relatively low temperature compared to the sol-gel method. For example, since the internal stress of the film generated during the crystallization process is small in the case of low-temperature manufacturing, it is considered that a piezoelectric thin film having a larger area than that of the conventional product and having no cracks can be formed.
[0004]
[Problems to be solved by the invention]
However, even in the piezoelectric element manufactured by the hydrothermal method, a minute gap or a portion having a weak bond between crystal grains may occur in the film thickness direction. Such a gap or a weakly coupled portion easily becomes a current path, and the withstand voltage characteristic is not always sufficiently obtained.
[0005]
Further, in the conventional hydrothermal method, when a thick film or a bulk material is to be formed, it is difficult to increase the thickness because the internal stress of the film generated during the crystallization process increases.
[0006]
Therefore, an object of the present invention is to provide a piezoelectric element including a piezoelectric film having a new structure excellent in withstand voltage characteristics. And it aims at providing the ink jet type recording head provided with this piezoelectric material element, and the printer provided with this ink jet type recording head. Another object of the present invention is to provide a method for manufacturing the piezoelectric film as described above, particularly a manufacturing method capable of increasing the thickness.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a piezoelectric element including a piezoelectric film, and a lower electrode and an upper electrode arranged with the piezoelectric film interposed therebetween, wherein the piezoelectric film includes a plurality of piezoelectric films. Each crystal layer is provided with a plurality of crystal grains, and in each crystal layer, a weak interface between the crystal grains extends in the film thickness direction, The interface with weak coupling in a certain crystal layer and the interface with weak coupling in a crystal layer adjacent thereto are formed discontinuously.
[0008]
Since the formation position of the weakly bonded surface between the crystal grains is different for each layer, the weakly bonded surface does not continue more than the thickness of one layer, so the current path connecting the upper electrode and the lower electrode Therefore, the piezoelectric element has a good withstand voltage.
[0009]
Further, the present invention is a piezoelectric element comprising a piezoelectric film, and a lower electrode and an upper electrode arranged with the piezoelectric film interposed therebetween, wherein the piezoelectric film has a plurality of crystal layers. Each crystal layer has a plurality of crystal grain groups each having a plurality of crystal grains, and the boundary surface between the crystal grain groups in each crystal layer extends in the film thickness direction. However, a boundary surface in a certain crystal layer and a boundary surface in a crystal layer adjacent thereto are formed discontinuously.
[0010]
Since the formation position of the boundary between crystal grain groups (for example, this boundary appears in the piezoelectric film as a weak crack or weak bond portion) is different for each layer, the micro crack or bond to the piezoelectric film. Even if a weak portion is generated, it does not continue more than the thickness of one layer of the plurality of layers of piezoelectric films, so that a current path hardly occurs and a piezoelectric element with good withstand voltage is obtained.
[0011]
According to the present invention, in an ink jet recording head including the piezoelectric element, a pressure chamber substrate in which a pressure chamber is formed, a diaphragm provided on one surface of the pressure chamber, and the vibration plate The piezoelectric element is provided at a position corresponding to the pressure chamber and configured to be able to change the volume of the pressure chamber.
[0012]
According to another aspect of the present invention, there is provided a recording medium transport mechanism configured to be able to supply and unload a recording medium, and an arbitrary recording medium supplied by the recording medium transport mechanism. And a head control circuit for printing at a position by the ink jet recording head.
[0013]
The present invention also relates to a method of manufacturing a piezoelectric element comprising a piezoelectric film, and a lower electrode and an upper electrode arranged with the piezoelectric film interposed therebetween, wherein the piezoelectric body includes an organometallic compound on the lower electrode. In this method, a precursor film is formed, and a process of hydrothermal treatment is performed a plurality of times, and the upper electrode is laminated on a plurality of piezoelectric films formed thereby.
[0014]
Since the process of forming and crystallizing the piezoelectric precursor film is repeatedly performed, even if a microcrack or a weakly bonded portion occurs in the piezoelectric body, the microcrack or the weakly bonded portion may extend over a plurality of layers. Absent. Therefore, it is possible to manufacture a piezoelectric element that hardly generates a current path. In addition, by stacking the piezoelectric bodies in multiple layers by this method, it is easy to increase the thickness, and it is possible to manufacture a piezoelectric element that is less likely to generate a current path even if a thick piezoelectric film or a bulk body is manufactured. .
[0015]
Further, the present invention provides a method for manufacturing the above piezoelectric element, wherein in each step executed a plurality of times, before forming the piezoelectric precursor film of each layer, a seed for generating a piezoelectric crystal is formed. It is good also as laminating | stacking a layer.
[0016]
Since a seed layer is formed between each layer of the piezoelectric film, crystal growth is promoted. In addition, since the seed layer is easily deposited in the microcracks generated in the lower layer, the crystal grows from the portion, and the possibility that the portion becomes the boundary of the crystal grains is reduced.
[0017]
The present invention is also a method of manufacturing the piezoelectric element, wherein the step of forming and crystallizing the piezoelectric precursor film is executed n (n is 2 or more) times to form an n-layer piezoelectric film. Among the steps executed n times, the piezoelectric precursor film formed in the first to (n-1) th steps is formed before the crystallization is completely performed in this step. The crystallization may be terminated and further crystallization may be performed in the next step.
[0018]
The process is terminated in the middle of crystallization, and the upper and lower layers are crystallized at the same time in the next step, whereby the bonding force between the layers of the piezoelectric film is increased. Further, the heating time for crystallization is short as a whole.
[0019]
The present invention is also a method for manufacturing an ink jet recording head comprising the piezoelectric element manufactured by the above manufacturing method, the step of forming a diaphragm on one surface of the substrate, and the piezoelectric element on the diaphragm. And a step of etching the substrate to form a pressure chamber.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0021]
(Printer structure)
FIG. 1 is an explanatory diagram of the structure of a printer in which an ink jet recording head having a piezoelectric element according to this embodiment is used. In this printer, a main body 2 is provided with a tray 3, a discharge port 4, and operation buttons 9. Furthermore, an ink jet recording head 1, a supply mechanism 6, and a control circuit 8 are provided inside the main body 2.
[0022]
The ink jet recording head 1 includes a piezoelectric element manufactured by the manufacturing method of the present invention. The ink jet recording head 1 is configured to be able to eject ink from nozzles in response to the ejection signal supplied from the control circuit 8.
[0023]
The main body 2 is a housing of the printer, and a supply mechanism 6 is arranged at a position where the paper 5 can be supplied from the tray 3, and the ink jet recording head 1 is arranged so that printing can be performed on the paper 5. The tray 3 is configured to be able to supply the paper 5 before printing to the supply mechanism 6, and the discharge port 4 is an outlet for discharging the paper 5 that has been printed.
[0024]
The supply mechanism 6 includes a motor 600, rollers 601 and 602, and other mechanical structures (not shown). The motor 600 is rotatable in response to the drive signal supplied from the control circuit 8. The mechanical structure is configured so that the rotational force of the motor 600 can be transmitted to the rollers 601 and 602. The rollers 601 and 602 are rotated when the rotational force of the motor 600 is transmitted, and the paper 5 placed on the tray 3 is drawn by the rotation, and is supplied by the head 1 so as to be printable. Yes.
[0025]
Although not shown, the control circuit 8 includes a CPU, a ROM, a RAM, an interface circuit, etc., and supplies a drive signal to the supply mechanism 6 in correspondence with print information supplied from a computer via a connector (not shown). An ejection signal can be supplied to the ink jet recording head 1. In addition, the control circuit 8 can perform operation mode setting, reset processing, and the like in response to an operation signal from the operation panel 9.
[0026]
FIG. 2 is an explanatory diagram of the structure of an ink jet recording head having the piezoelectric element of this embodiment. As shown in the drawing, the ink jet recording head 1 includes a nozzle plate 10, a pressure chamber substrate 20, and a vibration plate 30. This head constitutes an on-demand type piezo jet head.
[0027]
The pressure chamber substrate 20 includes a cavity (pressure chamber) 21, a side wall (partition wall) 22, a reservoir 23, and a supply port 24. The cavity 21 is a space for storing ink or the like formed by etching a substrate such as silicon. The side walls 22 are formed so as to partition the cavities 21. The reservoir 23 is a flow path for filling the cavities 21 with ink in common. The supply port 24 is formed so that ink can be introduced from the reservoir 23 into each cavity 21. The shape of the cavity 21 and the like can be variously modified by an ink jet method. For example, it may be a planar Kyser shape or a cylindrical Zoltan shape. Further, the cavity may be configured for one chamber type or may be configured for two chamber types.
[0028]
The nozzle plate 10 is bonded to one surface of the pressure chamber substrate 20 so that the nozzle holes 11 are disposed at positions corresponding to the cavities 21 provided in the pressure chamber substrate 20. The pressure chamber substrate 20 to which the nozzle plate 10 is bonded is further housed in a housing 25 to constitute the ink jet recording head 1.
[0029]
The diaphragm 30 is bonded to the other surface of the pressure chamber substrate 20. The diaphragm 30 is provided with a piezoelectric element (not shown). The vibration plate 30 is provided with an ink tank port (not shown) so that ink stored in an ink tank (not shown) can be supplied into the pressure chamber substrate 20.
[0030]
FIG. 3 is a sectional view for explaining a more specific structure of the ink jet recording head and the piezoelectric element of the present invention. This sectional view is an enlarged view of the cross section of one piezoelectric element. As shown in the figure, the diaphragm 30 is configured by laminating an insulating film 31 and a lower electrode 32, and the piezoelectric element 40 is configured by laminating a piezoelectric thin film layer 41 and an upper electrode 42. In particular, the ink jet recording head 1 includes a piezoelectric element 40, a cavity 21, and nozzle holes 11 connected at a constant pitch. The pitch between the nozzles can be appropriately changed in design according to the printing accuracy. For example, they are arranged to be 400 dpi (dot per inch).
[0031]
The insulating film 31 is made of a non-conductive material such as silicon dioxide (SiO2) formed by thermally oxidizing a silicon substrate.₂) And is deformed by deformation of the piezoelectric layer, so that the pressure inside the cavity 21 can be instantaneously increased.
[0032]
Although the lower electrode 32 is formed on the insulating film 31, a titanium or titanium oxide film (adhesion layer) of about 20 nm may be formed between the insulating film 31 and the lower electrode 32.
[0033]
The lower electrode 32 is one electrode for applying a voltage to the piezoelectric layer, and is made of a conductive material, such as platinum (Pt). The lower electrode 32 is not limited to this, and may be made of iridium (Ir), which is a metal having the same FCC structure as platinum. The lower electrode 32 is formed in the same region as the insulating film 31 so as to function as an electrode common to a plurality of piezoelectric elements formed on the pressure chamber substrate 20. However, it may be formed in the same size as the piezoelectric thin film layer 41, that is, in the same shape as the upper electrode.
[0034]
The upper electrode 42 is the other electrode for applying a voltage to the piezoelectric layer, and is made of a conductive material, for example, platinum (Pt) having a thickness of 0.1 μm.
[0035]
The piezoelectric thin film layer 41 is, for example, a piezoelectric ceramic crystal having a perovskite structure manufactured by the manufacturing method of the present invention, and is formed on the diaphragm 30 in a predetermined shape.
[0036]
The composition of the piezoelectric thin film layer 41 is, for example, lead zirconate titanate (Pb (Zr_{0 . 56}, Ti_{0 . 44}) O₃: PZT) or the like is used. In addition, lead lanthanum titanate ((Pb, La) TiO₃), Lead lanthanum zirconate ((Pb, La) ZrO)₃) Or lead zirconate titanate magnesium niobate (Pb (Mg, Nb) (Zr, Ti) O)₃: PMN-PZT), barium zirconate titanate (Ba (Zr, Ti) O)₃: BZT).
[0037]
A printing operation in the configuration of the ink jet recording head 1 will be described. When a drive signal is output from the control circuit 8, the supply mechanism 6 operates and the paper 5 is conveyed to a printable position by the head 1. When no discharge signal is supplied from the control circuit 8 and no voltage is applied between the lower electrode 32 and the upper electrode 42 of the piezoelectric element 40, the piezoelectric thin film layer 41 is not deformed. No pressure change occurs in the cavity 21 provided with the piezoelectric element 40 to which no ejection signal is supplied, and no ink droplet is ejected from the nozzle hole 11.
[0038]
On the other hand, when a discharge voltage is supplied from the control circuit 8 and a constant voltage is applied between the lower electrode 32 and the upper electrode 42 of the piezoelectric element 40, the piezoelectric thin film layer 41 is deformed. In the cavity 21 where the piezoelectric element 40 to which the discharge signal is supplied is provided, the vibration plate 30 is greatly bent. For this reason, the pressure in the cavity 21 increases instantaneously, and ink droplets are ejected from the nozzle holes 11. Arbitrary characters and figures can be printed by individually supplying ejection signals to the piezoelectric elements at the positions to be printed in the head.
[0039]
(Crystal structure)
FIG. 4 is a cross-sectional SEM photograph of a piezoelectric element according to an embodiment of the present invention, and FIG. 5 is a copy thereof. As shown in these drawings, four piezoelectric thin films (reference numeral 41 in FIG. 5) are stacked in the film thickness direction and sandwiched between the lower electrode 32 and the upper electrode 42.
[0040]
In each layer of the piezoelectric thin film 41, a plurality of crystal grain groups each having a plurality of crystal grains are formed, and the groups are separated by a boundary surface formed in the film thickness direction. Here, the boundary surface is not continuous with the boundary surface in the other layers, and is formed at different positions between adjacent layers. This greatly reduces the possibility of current leakage along the boundary surface. Therefore, even if a microcrack occurs during the crystallization process by the hydrothermal method, the microcrack is not linearly connected from the upper electrode to the lower electrode, so that current leakage is unlikely to occur and the withstand voltage characteristics are good. A simple piezoelectric element can be created.
[0041]
In these figures, the crystal grains are non-columnar. However, the present invention is not limited to this, and may be a columnar shape extending in the film thickness direction, which is a mixture of columnar crystal grains and non-columnar crystal grains. Also good. For example, if the crystal orientation of the piezoelectric thin film is [110] preferential orientation in the film thickness direction, it becomes columnar crystal grains, and if it is [111] preferential orientation in the film thickness direction, it becomes non-columnar crystal grains. In general, columnar crystal grains can provide better piezoelectric characteristics.
[0042]
(Production method)
Next, the manufacturing method of the piezoelectric element according to this embodiment will be described together with the manufacturing method of the ink jet recording head.
[0043]
Sol production
First, a piezoelectric ceramic sol as a raw material for the piezoelectric thin film layer is manufactured. For example, titanium tetraisopropoxide, pentaethoxyniobium and tetra-n-propoxyzirconium are mixed in 2-n-butoxyethanol and stirred at room temperature for 20 minutes. Then diethanolamine is added and stirred for another 20 minutes at room temperature. Add lead acetate and magnesium acetate and warm to 80 ° C. The mixture is stirred for 20 minutes in a warmed state, and then naturally cooled to room temperature. The metal alkoxide solution produced by the above steps is used as a precursor. However, the manufacturing method of sol is not limited to the above.
[0044]
Next, using the sol manufactured by the above manufacturing method, a piezoelectric element and further an ink jet recording head are manufactured. 6 and 7 are cross-sectional views of the manufacturing process of the piezoelectric element according to the present embodiment.
[0045]
Insulating film forming step (FIG. 6A)
The insulating film forming step is a step of forming the insulating film 31 on the silicon substrate 20. The thickness of the silicon substrate 20 is, for example, about 200 μm so that the height of the side wall does not become too high. The insulating film 31 is formed to a thickness of about 1 μm, for example. For the production of the insulating film, a known thermal oxidation method or the like is used to form a silicon dioxide film. Note that a titanium film or a titanium oxide film (adhesion layer 33) having a thickness of preferably 5 nm to 40 nm, more preferably about 20 nm may be further formed on the insulating film 31. The adhesion layer 33 improves the adhesion with the lower electrode 32.
[0046]
Lower electrode formation process (FIG. 6B)
This lower electrode formation step is a step of forming the lower electrode 32 on the insulating film 31 or the adhesion layer 33. For the lower electrode 32, for example, a platinum layer is laminated with a thickness of 200 nm. These layers are manufactured using a known electron beam evaporation method, sputtering method, or the like.
[0047]
Furthermore, a titanium (Ti) seed layer is preferably formed on the platinum film with a thickness of 3 nm to 25 nm, more preferably 5 nm. For example, a known DC sputtering method is used for forming the titanium seed layer. This seed layer is formed with a uniform thickness, but may be an island shape in some cases.
[0048]
Precursor film first layer forming step (FIG. 7C)
In the precursor film first layer forming step, by applying sol and drying / degreasing, the piezoelectric precursor thin film first layer 411 that is one of the piezoelectric films 41 composed of a plurality of layers is formed. It is a process of forming. First, the metal alkoxide solution produced as described above is applied on the lower electrode 32 to a certain thickness (for example, 0.2 μm). For example, when a known spin coating method is used, coating is performed at 500 rpm for 30 seconds, 1500 rpm for 30 seconds, and finally 500 rpm for 10 seconds. At the applied stage, each metal atom constituting PZT is dispersed as an organometallic complex. After application, it is dried at a constant temperature for a certain time. For example, the drying temperature is set to, for example, 150 ° C. or more and 200 ° C. or less. Preferably, it is dried at 180 ° C. The drying time is, for example, 5 minutes or more and 15 minutes or less. Preferably, it is dried for about 10 minutes.
[0049]
After drying, it is further degreased for a certain period of time at a certain degreasing temperature in an air atmosphere. The degreasing temperature is preferably in the range of 300 ° C to 500 ° C. This is because crystallization starts at a temperature higher than this range, and sufficient degreasing cannot be performed at a temperature lower than this range. Preferably, it is set to about 350 ° C. The degreasing time is, for example, 5 minutes or more and 90 minutes or less. This is because crystallization starts in a time longer than this range, and degreasing is not sufficient in a time shorter than this range. Preferably, degreasing is performed for about 10 minutes. The organic matter coordinated to the metal by degreasing dissociates from the metal, causes an oxidative combustion reaction, and scatters in the atmosphere.
[0050]
First hydrothermal treatment step (FIG. 7 (d))
In the hydrothermal treatment step, first, the alkaline solution 101 is filled in a water tank 100 configured to be able to apply pressure. Then, the piezoelectric precursor thin film first layer 411 laminated in the above process is immersed in the water tank 100 together with the substrate, and crystallization is promoted under a certain condition in an autoclave.
[0051]
In the case where an alkaline solution is used as the treatment liquid, for example, Ba (OH) is used here as the solute.₂Is used. KOH, Pb (OH)₂, Ba (OH)₂And Pb (OH)₂Or a mixture of KOH and Pb (OH)₂A mixed solution of It has been confirmed that piezoelectric ceramics crystallize with these alkaline solutions. The concentration of the alkaline solution is adjusted to a concentration of 0.05 M [mol / l] or more and 0.5 M [mol / l] or less. If the concentration is lower than this, crystallization is not promoted. If the concentration is higher than this, the alkali is strong and the piezoelectric thin film and the substrate may be eroded. For example, the concentration is adjusted to 0.1 M [mol / l].
[0052]
The temperature of the hydrothermal treatment is set to 120 ° C. or higher and 200 ° C. or lower. This is because crystallization is not promoted at a temperature lower than this range, and the piezoelectric thin film layer and the silicon substrate are etched at a temperature higher than this range. For example, the processing temperature is set to about 150 ° C. The pressure of the hydrothermal treatment is set to 2 atm or more and 20 atm or less. This is because good crystals cannot be obtained at pressures outside this range. For example, the pressure is set to about 6 atmospheres. The hydrothermal treatment time is set to 60 minutes, for example.
[0053]
When the piezoelectric precursor film first layer 411 is crystallized by this process, a minute crack or a weakly bonded portion between crystal grains occurs in the film thickness direction in the piezoelectric film first layer 41a due to internal stress. Sometimes. Although such a part may become a current path, such a fear is greatly reduced by going through the following steps.
[0054]
Precursor thin film second layer forming step (FIG. 7E)
On the piezoelectric thin film first layer 41a that has been subjected to hydrothermal treatment, by applying sol and drying / degreasing it, the piezoelectric body that becomes the second layer of the piezoelectric film 41 composed of a plurality of layers. This is a step of forming the precursor thin film second layer 412. Since the coating method, the drying method and the degreasing method are the same as those in the piezoelectric precursor thin film layer forming step, description thereof is omitted.
[0055]
It should be noted that a titanium (Ti) seed layer may be formed under the precursor film second layer 412 as well as under the piezoelectric precursor film first layer 411.
[0056]
In addition, the hydrothermal treatment is stopped before crystallization is completely performed in the first hydrothermal treatment step, and the precursor film first layer is simultaneously crystallized in the second hydrothermal treatment step described below. The layer may be further crystallized. Thereby, the adhesion between the piezoelectric first layer and the second layer is improved. Further, since the heating time per layer is short, the heating time for crystallization is short as a whole.
[0057]
Second hydrothermal treatment step (FIG. 7 (f))
In the second hydrothermal treatment step, hydrothermal treatment is again applied to the substrate. Hydrothermal treatment conditions are the same as the hydrothermal treatment step.
[0058]
Similarly to the first layer 41a, the piezoelectric film second layer 41b generated thereby may have a minute crack or a portion having a weak bond between crystal grains. However, according to the process of this embodiment, since the first layer and the second layer are crystallized separately, even if a microcrack occurs in one layer, it occurs in an unrelated place in the other layer. . Therefore, it is possible to avoid a situation in which a crack that extends from the upper electrode 42 to the lower electrode 32 occurs.
[0059]
Rather, if a microcrack is formed in the lower layer, the internal stress is absorbed at that location in the upper layer, so the possibility that a crack will occur at the same location as the crack in the lower layer is considered to be low. . In addition, when a seed layer is formed between the piezoelectric film first layer and the piezoelectric precursor film second layer, the seed layer is particularly easily deposited in the crack portion, so that the crystal of the piezoelectric film second layer is formed therefrom. Can be expected to grow epitaxially. Then, since the crystal grains of the piezoelectric film second layer are formed on the microcracks generated in the piezoelectric film first layer, there is little possibility that cracks will occur in the portion.
[0060]
In addition, according to the above manufacturing method, the piezoelectric film is formed over a plurality of layers by repeatedly performing the piezoelectric precursor thin film layer forming step and the hydrothermal treatment step, and the film thickness can be increased. For example, when a piezoelectric film having a thickness of 0.2 μm per layer is laminated over 10 layers, a total of 2 μm piezoelectric films can be obtained. Further, it can be formed to a thickness larger than that (for example, a bulk body having a thickness of about 15 μm).
[0061]
As described above, the piezoelectric precursor film used in the piezoelectric element of the present embodiment is completed by crystallizing the piezoelectric precursor film every time it is formed. Next, a manufacturing method of a piezoelectric element using the piezoelectric film and an ink jet head as an example of a piezoelectric actuator including the piezoelectric element will be described. FIG. 8 is a cross-sectional view for explaining the formation process of the piezoelectric element for forming the upper electrode on the piezoelectric film, and the manufacturing process of the ink jet head equipped with this.
[0062]
Upper electrode formation process (FIG. 8A)
An upper electrode 42 is formed on the piezoelectric thin film layer 41 using a technique such as an electron beam vapor deposition method or a sputtering method. Platinum (Pt) or the like is used as the material of the upper electrode. The thickness is about 100 nm.
[0063]
The layer structure of the piezoelectric element is completed through the above steps. This layer structure may be formed by etching or the like into a shape suitable for an ink jet recording head to which a piezoelectric element is applied.
[0064]
Etching process (FIG. 8B)
The etching process is a process for forming the piezoelectric element 40. First, the laminated structures 41 and 42 of the piezoelectric element are masked so as to have a shape matching the cavity formed in the pressure chamber substrate 20. Then, the periphery is etched to form the piezoelectric element 40. Specifically, first, a resist material having a uniform thickness is applied using a spinner method, a spray method, or the like. Next, a mask is formed in the shape of the piezoelectric element, and then exposed and developed to form a resist pattern on the upper electrode 42. The mask is formed according to whether the resist material is a positive type or a negative type. Then, the upper electrode 42 and the piezoelectric thin film layer 41 are etched and removed by applying commonly used ion milling or dry etching. Thus, the piezoelectric element 40 suitable for the ink jet recording head can be formed.
[0065]
Pressure chamber forming process (FIG. 8C)
The pressure chamber forming step is a step of forming the cavity 21 by etching the other surface of the pressure chamber substrate 20 on which the piezoelectric element 40 is formed. The cavity 21 space is etched from the side opposite to the surface on which the piezoelectric element 40 is formed by using anisotropic etching using an active gas such as anisotropic etching or parallel plate type reactive ion etching. The portion left without being etched becomes the side wall 22.
[0066]
Nozzle plate bonding process (Fig. 8 (d))
The nozzle plate bonding step is a step of bonding the nozzle plate 10 to the etched silicon substrate 20 with an adhesive. Alignment is performed so that each nozzle hole 11 is arranged in the space of each cavity 21 at the time of bonding. Finally, the pressure chamber substrate 20 to which the nozzle plate 10 is bonded is attached to the housing, and the ink jet recording head 1 is completed.
[0067]
In the case where the nozzle plate and the pressure chamber substrate are integrally formed by etching, the nozzle plate bonding step is not necessary. That is, it is only necessary to etch the pressure chamber substrate into a shape that combines the nozzle plate and the pressure chamber substrate, and finally provide a nozzle hole at a position corresponding to the cavity.
[0068]
(Example)
As an example of the above production method, lead zirconate titanate (Pb (Zr_0.56Ti_0.44) O₃) Was manufactured using a piezoelectric thin film layer. In particular, the process of applying and crystallizing the piezoelectric precursor film was repeated twice to form piezoelectric crystals in two layers.
[0069]
On the other hand, a piezoelectric thin film manufactured by a conventional hydrothermal method is given as a comparative example. The piezoelectric thin film of the comparative example was manufactured by forming a PZT precursor film on a lower electrode made of titanium (Ti) and crystallizing it by hydrothermal treatment. In both cases, the piezoelectric thin film had a diameter of 2 mm and the film thickness was 0.5 μm.
[0070]
FIG. 9 is a graph showing voltage-current characteristics when a DC voltage is applied to the piezoelectric elements according to the present example and the comparative example. In the figure, the white dots are the characteristics of the piezoelectric element according to this embodiment, and the black dots are the characteristics of the piezoelectric element according to the comparative example. As shown in this figure, it can be seen that the piezoelectric element according to the present example has a leakage current with respect to voltage application that is significantly smaller than the leakage current of the piezoelectric element according to the comparative example.
[0071]
In this embodiment, the number of crystals is two. However, if the number of layers is increased, the current path formed along the boundary of the crystal grain group becomes longer, so that the value of the leakage current with respect to the applied voltage is considered to be further reduced. .
[0072]
(Other variations)
The present invention is not limited to the above embodiment and can be applied with various modifications. For example, although the above embodiment is PZT, other piezoelectric ceramics (such as PMN-PZT) for piezoelectric elements can be similarly crystallized by the hydrothermal method.
[0073]
In addition, the piezoelectric element manufactured according to the present invention is used not only for the pressure generation source of the ink jet recording head, but also for manufacturing a piezoelectric element device such as a piezoelectric fan, an ultrasonic motor, an ultrasonic vibrator, and such a device. Can adapt. That is, since the piezoelectric element of the present invention can be increased in area and cost can be reduced, it is possible to provide an application that does not exist in a conventional product or to provide a conventional function at a lower price.
[0074]
【The invention's effect】
According to the present invention, it is possible to provide a highly reliable piezoelectric element having excellent voltage resistance and improved mechanical strength due to low internal stress. In addition, it is possible to provide a piezoelectric element including a piezoelectric body excellent in piezoelectricity and ferroelectricity.
[0075]
In addition, according to the present invention, it is possible to provide a method for manufacturing a piezoelectric element having the above-described characteristics, and to provide a manufacturing method capable of increasing the thickness.
[Brief description of the drawings]
FIG. 1 is a perspective view illustrating the structure of a printer in which an ink jet recording head having a piezoelectric element according to an embodiment is used.
FIG. 2 is an explanatory diagram of the structure of an ink jet recording head having the piezoelectric element of the present embodiment.
FIG. 3 is a cross-sectional view illustrating a specific structure of an ink jet recording head and a piezoelectric element according to the present invention.
FIG. 4 is a cross-sectional SEM photograph of a piezoelectric element according to an embodiment of the present invention.
FIG. 5 is a copy of FIG.
FIG. 6 is a cross-sectional view of a manufacturing process of the piezoelectric element according to the present embodiment.
FIG. 7 is a cross-sectional view of a manufacturing process of the piezoelectric element according to the present embodiment.
FIG. 8 is a manufacturing process cross-sectional view illustrating a method for manufacturing an ink jet recording head of the present invention.
FIG. 9 is a graph showing voltage-current characteristics when a direct current voltage is applied to piezoelectric elements according to examples and comparative examples of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Nozzle plate, 20 ... Pressure chamber board | substrate, 30 ... Diaphragm, 31 ... Insulating film, 32 ... Lower electrode, 40 ... Piezoelectric element, 41 ... Piezoelectric thin film layer, 42 ... Upper electrode, 21 ... Cavity

Claims (3)

A piezoelectric element comprising a piezoelectric film, and a lower electrode and an upper electrode arranged with the piezoelectric film interposed therebetween,
In the piezoelectric film , a plurality of crystal grain groups each having a plurality of crystal grains are formed in the film surface direction and the film thickness direction, and a boundary surface between the crystal grain group and another crystal grain group extends in the film thickness direction. The existing crystal layer is laminated,
There the boundary surface in the crystal layer and said boundary surface in another crystal layer in contact with the crystal layer is discontinuously formed in the thickness direction, the piezoelectric element. An ink jet recording head comprising the piezoelectric element according to claim 1.
A pressure chamber substrate on which the pressure chamber is formed;
A diaphragm provided on one surface of the pressure chamber;
An ink jet recording head comprising: the piezoelectric element provided at a position corresponding to the pressure chamber of the vibration plate and configured to be capable of changing a volume of the pressure chamber. In the printer provided with the ink jet recording head according to claim 2,
A recording medium transport mechanism configured to be able to supply and unload the recording medium;
And a head control circuit that causes the ink jet recording head to print at an arbitrary position on the recording medium supplied by the recording medium transport mechanism.

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