JPH11307834A - Piezoelectric element, ink jet recording head, and method for producing them - Google Patents

Abstract

(57) [Problem] To provide a piezoelectric element having many <001> orientations. SOLUTION: Between a lower electrode (32) and an upper electrode (43), a first layer piezoelectric thin film (41) formed from a precursor not containing a polymer organic material and a polymer organic material are included. A second-layer piezoelectric thin film (42) formed from a precursor. First
The layer (41) is crystallized with a large proportion of <001> orientation, but is thin because cracks are easily generated. Since the second layer (42) contains a high-molecular organic material, it can be made thick without causing cracks, and has many crystal grains (44). During the crystal growth, the crystal grows by inheriting the crystal structure of the first layer (41), so that the <001> orientation is increased as a whole, and the piezoelectric characteristics are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element used in an ink jet recording head and the like, and more particularly, to a piezoelectric element having good piezoelectric characteristics by clarifying the conditions of a solvent in a metal alkoxide solution used as a material for a piezoelectric thin film. An element is provided.

[0002]

2. Description of the Related Art A piezoelectric element is an element exhibiting an electromechanical conversion function, and is made of a ferroelectric or paraelectric crystallized piezoelectric ceramic. JP-A-3-
No. 69512 and US Pat. No. 4,830,996 disclose a metal alkoxide solution prepared by dissolving a piezoelectric ceramic material in a solvent, applying the solution by a sol-gel method, and applying a heat treatment thereto. A technology for manufacturing a body element has been disclosed. When the metal alkoxide solution crystallizes, a perovskite crystal structure is formed,
The characteristics of the piezoelectric element change depending on the orientation of the crystal plane. The orientation of the crystal plane is determined by various factors.
In particular, the paper "Investigation of the drying temperature
dependence of the orientation in sol-gel processe
d PZT thin films ", Journal of materials science 32
(1997), Chang Jung Kim et al., Pp1213-1219,
It is disclosed that high molecular organic matter remaining after crystallization affects the orientation.

For example, PZT (lead zirconate titanate)
When a crystal is dried at a relatively low temperature with respect to a ferroelectric piezoelectric ceramic such as
The paper describes that the orientation increases and the residual amount of organic substances decreases and the <001> orientation increases as the drying temperature increases. According to the same paper, PZT with controlled orientation has a low processing voltage, exhibits high spontaneous polarization and remanent polarization in hysteresis characteristics between an applied electric field and polarization, and exhibits high quality piezoelectric characteristics. It is described that a <001> oriented thin film has a higher pyroelectric coefficient than a crystal of another orientation.

Therefore, a piezoelectric element having good piezoelectric characteristics can be achieved by increasing the ratio of <001> orientation, and it is considered that the amount of high-molecular organic matter remaining after crystallization should be reduced. For example, if a polymer material that thermally decomposes at a low temperature is used, it is expected that a residual amount of the polymer organic material can be reduced to provide a piezoelectric element having good piezoelectric characteristics.

[0005]

However, if the molecular weight of the organic substance constituting the solvent is reduced unilaterally, there is a problem that cracks are easily generated in the piezoelectric thin film due to stress during manufacturing. That is, the high molecular organic substance added as a solvent has a function of preventing the occurrence of cracks. From the above paper, it is considered that the residual amount of high molecular organic matter is determined by the relationship between the thermal decomposition temperature and the heat treatment temperature in the degreasing process, and an appropriate degreasing temperature is necessary to obtain piezoelectric ceramics with good crystallinity. It is said. For this reason,
It was not possible to lower the degreasing temperature just to reduce the residual amount.

For example, in the paper "Extended x-ray absorption f
ine structure determination of local structure in
sol-gel-derived lead titanate, lead zirconate and
leadzirconate titanate ", J. Mater. Res., Vol 10, N
o. 6, 1995-6, Materials Research Society, SS Se
According to ngupta et al., it is described that the optimal crystallization temperature (degreasing temperature) of PZT is 425 ° C. Therefore, in order to obtain a piezoelectric element having a good <001> orientation, a high-molecular organic substance having a thermal decomposition temperature of about 400 ° C. is considered preferable. Was previously unknown.

[0007] In view of the above circumstances, the inventor of the present application considered the conditions of the solvent in the metal alkoxide solution, and was able to perform crystallization at an optimal degreasing temperature, and
An attempt was made to manufacture a piezoelectric element having many 001> orientations and <100> orientations and good piezoelectric properties. <001>
Since the orientation and the <100> orientation are equivalent and it is practically impossible to separate them, the <001> orientation in the present invention will be referred to as the <100> orientation unless otherwise specified in the <100> orientation. It also includes orientation.

[0008]

That is, a first object of the present invention is to provide a layer structure and a crystal structure of a piezoelectric element exhibiting suitable piezoelectric characteristics.

A second object of the present invention is to provide an ink jet recording head using a piezoelectric element exhibiting favorable piezoelectric characteristics.

A third object of the present invention is to provide a method of manufacturing a piezoelectric element for performing degreasing at an appropriate degreasing temperature and setting the <001> orientation and the <100> orientation to be superior to other orientations. Is to improve the piezoelectric characteristics of the piezoelectric element.

A fourth object of the present invention is to provide a method of manufacturing an ink jet recording head having a piezoelectric element exhibiting good piezoelectric characteristics.

[0012] The invention for solving the above first object is a piezoelectric element having a piezoelectric thin film sandwiched between a lower electrode and an upper electrode, wherein the piezoelectric thin film is formed on the lower electrode and has a fine crystal grain density. And a second layer formed on the first layer and having a high fine crystal grain density. Since the first layer is manufactured from a metal alkoxide solution containing no organic polymer, there are few microcrystalline particles. On the other hand, since the second layer is manufactured from a metal alkoxide solution containing a high molecular organic substance in order to make the film thick, it has a large number of microcrystalline particles. For example, the fine crystal grain density of the first layer is set to 1 × 10 ⁶ / cm ² or less. For example, the fine crystal grain density of the second layer is 1 ×
It is set to 10 ⁸ / cm ² or more.

In the piezoelectric thin film, the ratio of the <001> -oriented and <100> -oriented crystal axes is larger than that of the <111> -oriented crystal axis. Since the first layer is crystallized from a metal alkoxide solution containing no organic polymer,
The 001> or <100> orientation is dominant. Since the second layer grows using the columnar crystals grown from the first layer as seeds, the crystal structure of the second layer also has a <001> orientation or <1
00> orientation becomes dominant.

However, the first layer has a thickness of 0.05 μm or more and a thickness of 0.1 μm.
It is formed with a thickness of 4 μm or less. Since the first layer does not contain a high molecular organic substance which plays a role of preventing cracks, cracks are easily generated in the manufacturing process, so that the thickness is 0.4 μm or less. Further, in order to generate sufficient columnar crystals and to act as seeds of the second layer laminated on the upper part, the thickness is required to be 0.05 μm or more. As described above, the first layer must be thin, but the second layer can be made thicker.
The entire thin film can be formed with a thickness of 1.0 μm or more. Specifically, the metal alkoxide constituting the piezoelectric thin film is made of lead zirconate titanate (Pb (Zr, Ti) O
₃ : PZT), lanthanum lead titanate ((Pb, La) T
iO ₃ ), lead lanthanum zirconate titanate ((P
b, La) (Zr, Ti) O ₃ : PLZT) or lead magnesium zirconate titanate niobate (Pb (M
_{g, Nb) (Zr, Ti} ) O 3: containing PMN-PZT) or a piezoelectric ceramic of.

According to the invention for solving the second problem, in an ink jet recording head provided with the piezoelectric element of the present invention, a pressure chamber substrate in which a pressure chamber is formed, and a vibration for closing one surface of the pressure chamber. A piezoelectric element provided at a position corresponding to the pressure chamber of the vibration plate and configured to be able to apply a volume change to the pressure chamber.

According to a third aspect of the present invention, there is provided a method of manufacturing a piezoelectric element in which a piezoelectric thin film having an electromechanical conversion action is sandwiched between a lower electrode and an upper electrode. Forming a first layer using a metal alkoxide solution prepared by dissolving a ceramic material in a solvent other than a polymer organic material, and forming a piezoelectric ceramic material on a solvent of the polymer organic material on the first layer. Forming a second layer using a metal alkoxide solution produced by dissolution; and forming a piezoelectric thin film by the step. Since the first layer does not contain a polymer organic material, the <001> orientation or the <100> orientation becomes dominant. Since the crystal grows on the second layer using the columnar crystal of the first layer as a seed, <001 is obtained in the same manner as the crystal orientation of the first layer.
> Orientation or <100> orientation dominates. And second
Since the layer contains a polymer organic material, it can be made thicker. Therefore, the manufactured piezoelectric element is generally <0
The <01> orientation and the <100> orientation are dominant and have good piezoelectric properties.

Here, the step of forming the first layer and the step of forming the second layer include a) a step of applying a sol, which is a metal alkoxide solution, to a certain thickness, and b) a step of applying the applied sol to a certain thickness. Drying by heating in an atmosphere
Degreasing step. This is a so-called sol-gel method.

In the step of forming the first layer, the first layer
The layer is formed with a thickness of not less than 0.05 μm and not more than 0.4 μm. Since the first layer does not contain a high molecular organic substance which plays a role of preventing cracks, cracks are easily generated in the manufacturing process, so that the thickness is 0.4 μm or less. Further, in order to generate sufficient columnar crystals and to act as seeds of the second layer laminated on the upper part, the thickness is required to be 0.05 μm or more. In the step of forming the first layer, it is preferable to perform degreasing by setting the degreasing temperature to a temperature of 430 ° C. or more and 500 ° C. or less. This is because a crystal structure in which the <001> orientation is dominant can be formed in this temperature range.

In the step of forming the second layer, polyethylene glycol having a molecular weight of 400 or more and 600 or less is used as a solvent for the metal alkoxide solution. With such an organic solvent, the optimal degreasing temperature is from 400 ° C to 45 ° C.
This is because it has a thermal decomposition temperature between 0 ° C.

In the step of forming the second layer, degreasing is performed by setting the degreasing temperature to a temperature of 375 ° C. or more and 425 ° C. or less. This is because, when degreasing is performed at this temperature, optimal crystallization is performed. In particular, it is preferable to perform degreasing by setting the degreasing temperature to 400 ° C. This is because the thickest film can be formed at this temperature.

For example, as a metal alkoxide solution, lead zirconate titanate (Pb (Zr, Ti) O ₃ : PZ
T), lanthanum lead titanate ((Pb, La) Ti
O ₃ ), lanthanum lead zirconate titanate ((Pb,
La) (Zr, Ti) O ₃ : PLZT) or lead magnesium zirconate titanate niobate (Pb (Mg,
A solution containing any one of Nb) (Zr, Ti) O ₃ : PMN-PZT is used.

According to a fourth aspect of the present invention, there is provided a method of manufacturing an ink jet recording head including a piezoelectric element manufactured by the manufacturing method of the present invention, comprising the steps of: forming a vibration plate on one surface of a substrate; The method includes the steps of manufacturing a piezoelectric element on a vibration plate, and forming a pressure chamber by etching a substrate in such an arrangement that the vibration plate provided with the piezoelectric element forms one surface of the pressure chamber.

[0023]

Embodiments of the present invention will now be described with reference to the drawings. In this embodiment, a piezoelectric element and an ink jet recording head are manufactured by using the manufacturing method of the present invention.

(Structures of Inkjet Recording Head and Piezoelectric Element) First, the structure of the inkjet recording head will be described. FIG. 2 is an exploded perspective view of the ink jet recording head of this embodiment. FIG. 3 is a partial cross-sectional view of a main part of the ink jet recording head. As shown in FIG. 2, the ink jet recording head 1 includes a nozzle plate 10, a pressure chamber substrate 20, a vibration plate 30, and a housing 25. The piezoelectric element according to the present invention is provided on the back side of the diaphragm 30 in FIG.

As shown in FIGS. 2 and 3, the pressure chamber substrate 20 includes a cavity 21, a side wall (partition) 22, and a reservoir 2.
3 and a supply port 24. The cavity 21
The pressure chamber is a space for storing ink or the like formed by etching a substrate such as silicon for discharging. The side wall 22 is formed so as to partition between the cavities 21. The reservoir 23 is a flow path for filling the respective cavities 21 with ink in common. The supply port 24 is connected to each cavity 21 from the reservoir 23.
Is formed so as to be able to introduce ink.

The nozzle plate 10 is bonded to one surface of the pressure chamber substrate 20 so that the nozzle holes 11 are arranged 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 fitted into a housing 25 as shown in FIG.

The vibration plate 30 is bonded to the other surface of the pressure chamber substrate 20. The vibration plate 30 is provided with the piezoelectric element 40 of the present invention. The piezoelectric element 40 is a crystal of a piezoelectric ceramic having a perovskite structure,
It is formed in a predetermined shape on the diaphragm 30.

FIG. 1 is a sectional view illustrating the layer structure of a piezoelectric element 40 according to the present invention. The piezoelectric element 40 includes a lower electrode 32, piezoelectric thin film layers 41 and 42 and an upper electrode 43 in FIG. 1, and it is possible to manufacture and use only the piezoelectric element independently. In this embodiment, the diaphragm 3 of the ink jet recording head 1 is used for use as an actuator of the ink jet recording head.
0.

As shown in FIG. 1, the vibration plate 30
1 and a lower electrode 32, and the piezoelectric element 40 is formed by laminating a piezoelectric thin film layer 41 and an upper electrode 42. As shown in FIG.
In addition to the configuration in which the lower electrode is formed in the same region as the first electrode, a configuration in which the lower electrode is formed only in the region of the piezoelectric element, that is, in the same shape as the upper electrode, can be adopted. The insulating film 31 is made of a material having no conductivity, for example, silicon dioxide formed by thermally oxidizing a silicon substrate or the like. The insulating film 31 is deformed by the volume change of the piezoelectric layer, and instantaneously increases the pressure inside the cavity 21. It is configured to be possible.

The lower electrode 32 is an electrode paired with the upper electrode 43 for applying a voltage to the piezoelectric layer, and has a conductive material, for example, a titanium (Ti) layer, platinum (Pt).
And a titanium (Ti) layer. The reason why the plurality of layers are stacked to form the lower electrode is to increase the adhesion between the platinum layer and the piezoelectric layer and between the platinum layer and the insulating film. The upper electrode film 43 serves as 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.

The first layer 41 is a piezoelectric thin film layer, particularly a piezoelectric thin film layer formed without using a polymer organic material. Since no high-molecular organic material is used, the density of the crystal grains 44 in the first layer 41 is 1 × 10 ⁶ / cm ² or less. After the drying, degreasing, and high-speed heat treatment, the solvent component evaporates, so that the first layer and the second layer have the same piezoelectric ceramic crystal structure except for the difference in the fine particle density. For example, lead zirconate titanate (Pb (Zr, Ti) O ₃ : PZT), lead lanthanum titanate ((Pb, La) TiO ₃ ), lead lanthanum zirconate titanate ((Pb, La) (Zr, Ti) ) _O 3:
PLZT) or lead magnesium zirconate titanate niobate (Pb (Mg, Nb) (Zr, Ti) O ₃ :
PMN-PZT) is formed of any of ferroelectric piezoelectric ceramics. A typical specific composition is PMN-PZT having a composition ratio of Pb (Mg _1/3 Nb _2/3 ) _0.1 Zr _0.5 Ti _0.4 O ₃ (1).

The first layer 41 has a thickness of at least 0.05 μm and a thickness of 0.4 μm.
It is formed to a thickness of μm or less. Since the first layer does not contain a high molecular organic substance which plays a role of preventing cracks, cracks are easily generated in the manufacturing process, so that the thickness is 0.4 μm or less. In addition, sufficient columnar crystals are formed, and the second
In order to act as a seed for the layer 42, a thickness of 0.05 μm or more is required. In the first layer 41, the crystal axes having the <001> orientation are larger than the crystal axes having the other orientation. This is because crystallization was performed without using a high-molecular organic material.

The second layer 42 is a piezoelectric thin film layer, in particular, a piezoelectric thin film layer formed using a polymer organic material. Since a high molecular weight organic material is used, the crystal grains 44
Is higher than that of the first layer 41 and is 1 × 10 ⁸ / cm ² or more. After the drying, degreasing, and high-speed heat treatment, the solvent component has evaporated, so that the second layer 42
It has the same piezoelectric ceramic composition as the layer 41.

Further, since the second layer 42 is manufactured from a metal alkoxide solution using a high-molecular organic material as a solvent, cracks do not occur in the manufacturing process. Therefore, it can be formed to a thickness of 0.6 μm or more so that good piezoelectric characteristics can be obtained. However, if the thickness of the piezoelectric thin film is too large, the driving voltage increases. Therefore, the thickness of the entire piezoelectric thin film is adjusted to be 2.0 μm or less.

The principle of ejecting ink droplets in the structure of the ink jet recording head will be described. Piezoelectric element 40
When no voltage is applied between the lower electrode 32 and the upper electrode 43, no volume change occurs in the piezoelectric thin film. No pressure change occurs in the cavity 21 in which the piezoelectric element 40 to which the voltage is not applied is provided, and no ink droplet is ejected from the nozzle hole 11.

On the other hand, when a constant voltage is applied between the lower electrode 32 and the upper electrode 42 of the piezoelectric element 40, the volume of the piezoelectric thin film changes. In the cavity 21 in which the piezoelectric element 40 to which the voltage is applied is provided, the vibration plate 3
0 flexes greatly. Therefore, the pressure in the cavity 21 increases instantaneously, and ink droplets are ejected from the nozzle holes 11.

(Description of Manufacturing Method) Next, a method of manufacturing an ink jet recording head according to the present invention will be described together with a method of manufacturing a piezoelectric element.

Production of Sol: A sol of piezoelectric ceramics, which is a raw material of a piezoelectric thin film layer, is produced. Both the first layer 41 and the second layer 42 are manufactured from a metal alkoxide solution for forming the same piezoelectric ceramic. However, a polymer organic material is not used for the metal alkoxide solution for manufacturing the first layer 41, and a polymer organic material is used for the metal alkoxide solution for manufacturing the second layer 42.

More specifically, a metal alkoxide solution is produced by using a material shown in Table 1 as a solute and a basic solvent of the piezoelectric thin film layer.

[0040]

[Table 1]

First, titanium tetraisopropoxide, pentaethoxyniobium and tetra-n-propoxyzirconium are mixed in 2-n-butoxyethanol, and the mixture is stirred at room temperature for 20 minutes. Then, diethanolamine is added and the mixture is further stirred at room temperature for 20 minutes. Add lead acetate and magnesium acetate and heat to 80 ° C. The mixture is stirred for 20 minutes while being heated, and then naturally cooled to room temperature. The metal alkoxide solution manufactured in the above steps is used as a precursor for manufacturing the first layer 41.

Further, as a high molecular organic material in the above solution,
Polyethylene glycol having a molecular weight of 400 to 600 (PE
G) in a molar ratio to PZT of 95 mol% or more
mol% or less, preferably about 75 mol%. This is because the inclusion of the high-molecular-weight organic material can prevent the occurrence of cracks. The metal alkoxide solution to which the polymer organic material has been added is used as a precursor for producing the second layer 42.

Next, a method for manufacturing the piezoelectric element and the ink jet recording head of this embodiment using the sol manufactured by the above-described manufacturing method will be described with reference to the manufacturing process sectional views of FIGS. Among them, the method of manufacturing a piezoelectric element includes a lower electrode forming step, a first layer forming step, a second forming step, and an upper electrode forming step.

Insulating Film Forming Step (FIG. 4A): The insulating film forming step is a step of forming an insulating film 31 on the silicon substrate 20. The silicon substrate 20 has a thickness of, for example, about 200 μm, and the insulating film 31 has a thickness of about 1 μm. For the production of the insulating film, a known thermal oxidation method or the like is used.

Lower electrode forming step (FIG. 4B): In the lower electrode forming step, a lower electrode 32 is formed on the insulating film 31. The lower electrode 32 is formed, for example, by forming a titanium layer, a titanium oxide layer, a titanium layer, a platinum layer, and a titanium layer by 0.01 μm.
m, 0.01 μm, 0.005 μm, 0.5 μm, 0.
Laminate to a thickness of 005 μm. These layers are manufactured by a known direct current sputtering method or the like.

First Layer Forming Step (FIG. 4 (c)): The first layer forming step uses a metal alkoxide solution containing no high-molecular organic material as a solvent by a sol-gel method.
1 is a step of forming First, apply this solution to the lower electrode 32
Apply a certain thickness on top. For example, when a known spin coating method is used, 500 rotations per minute for 30 seconds, 1 minute per minute
The coating is performed at 500 rotations for 30 seconds and finally at 500 rotations per minute for 10 seconds. At the stage of application, each metal atom constituting PZT is dispersed as an organometallic complex. After the application, the coating is dried at a constant temperature (for example, 180 degrees) for a certain time (for example, about 10 minutes). Drying causes the solvent butoxyethanol to evaporate. After drying, degreasing is further performed at a constant degreasing temperature in an air atmosphere for a certain time (30 minutes). The degreasing temperature is at least 430 ° C or higher and 500 ° C or lower.

Since the first layer uses a metal alkoxide solution containing no high-molecular-weight organic material, cracks are easily generated. Therefore, it is necessary to set an optimum temperature range in which crystallization can be promoted without cracks. Because there is. The organic matter coordinated to the metal is dissociated from the metal by degreasing, and then undergoes an oxidative combustion reaction, which flies into the atmosphere. This application → drying →
Each step of degreasing is repeated a predetermined number of times, for example, four times, and four thin film layers are laminated. The multi-layering is intended to form a piezoelectric thin film layer having a thickness capable of acting as a crystal seed of the second layer while preventing the occurrence of cracks. This first layer 4
No. 1 is liable to cause cracks, so it is necessary to suppress the thickness to 0.4 μm or less at the maximum.

After forming the first layer 41, rapid thermal processing (RTA) is performed at a constant temperature. For example, in an oxygen atmosphere, heating is performed at 600 degrees for 5 minutes, and further at 725 degrees for 1 minute. By this high-speed heat treatment, a perovskite crystal structure is formed from the gel in the amorphous state. Usually, when the lower electrode is formed of Pt, crystals of <111> orientation grow, but since the high-molecular-weight organic material is not contained as a solvent, the ratio of <001> orientation increases and the ratio of <0> increases.
The 01> oriented columnar crystal also grows together with the <111> oriented columnar crystal.

Second Layer Forming Step (FIG. 4D): The second layer forming step is to form a second layer on the first layer 41 by a sol-gel method using a metal alkoxide solution containing a polymer organic material. This is a step of forming the two layers 42. A solution using the above polyethylene glycol as a solvent is applied on the first layer 41 to a certain thickness. For example, when a known spin coating method is used, coating is performed at 500 rotations per minute for 30 seconds, at 1500 rotations per minute for 30 seconds, and finally at 500 rotations per minute for 10 seconds. At the stage of application, each metal atom constituting PZT is dispersed as an organometallic complex. After the application, the coating is dried at a constant temperature (for example, 180 degrees) for a certain time (for example, about 10 minutes). Drying causes the solvent butoxyethanol to evaporate. After drying, degreasing is further performed at a constant degreasing temperature in an air atmosphere for a certain time (30 minutes). This degreasing temperature is
At least 375 ° C or higher and 425 ° C or lower. In this temperature range, the organic material such as polyethylene glycol coordinated with the metal dissociates from the metal to cause a thermal oxidation reaction and disperses in the atmosphere.

Since the solution of the second layer 42 contains a high-molecular organic material, cracks are unlikely to occur. This application → drying →
Each step of degreasing is repeated a predetermined number of times, for example, six times, and six thin film layers are laminated. The multi-layering is intended to increase the film thickness while preventing the occurrence of cracks. After laminating a plurality of thin film layers, rapid thermal processing (RTA) is performed at a constant temperature.
For example, in an oxygen atmosphere, heating is performed at 600 degrees for 5 minutes, and further at 725 degrees for 1 minute. By this high-speed heat treatment, a perovskite crystal structure is formed from the gel in the amorphous state. In the thin film layer, columnar crystals grow upward using the crystals in the first layer 41 as seeds. <001 in the first layer 41
Since the <001> oriented columnar crystal is also included, the <001> oriented first layer columnar crystal portion takes over this orientation, and the <001> oriented columnar crystal also grows in the second layer thin film layer. I do.

After laminating 10 layers, 6 layers are formed in an oxygen atmosphere.
High-speed heat treatment is performed by heating at 50 ° C. for 5 minutes and further at 900 ° C. for 1 minute. By these heat treatments, a perovskite crystal structure is formed from the gel in the amorphous state. Although the first layer 41 cannot be made thicker, the second layer 42 contains a high molecular weight organic material, so that cracks do not occur and the second layer 42 can be made thicker. Therefore, the entire piezoelectric thin film can have a thickness of 1.0 μm or more.

Upper electrode forming step (FIG. 4E): An upper electrode 43 is further formed on the second layer 42 by using a technique such as an electron beam evaporation method or a sputtering method. As a material of the upper electrode, platinum (Pt) or the like is used. The thickness is about 100 nm.

Etching Step (FIG. 5A): In the etching step, the laminated structures 41, 42 and 43 are masked so as to have a shape conforming to each cavity 21, and the periphery thereof is etched to form the piezoelectric element 40. It is a process. Specifically, first, a resist material having a uniform thickness is applied using a method such as a spinner method or a spray method. Next, a mask is formed in the shape of the piezoelectric element, and then exposed and developed,
A resist pattern is formed on the upper electrode 43. The upper electrode 43 and the first and second layers 41 and 42, which are the piezoelectric thin film layers, are etched and removed by applying ion milling, dry etching, or the like which is usually used for this purpose. Thus, the piezoelectric element 40 can be formed. If this piezoelectric element is configured so that a voltage can be applied between the upper electrode and the lower electrode, it is possible to function as an independent electromechanical transducer. In this embodiment, an ink jet recording head is further manufactured.

Pressure Chamber Forming Step (FIG. 5B): The pressure chamber forming step is a step of forming the pressure chamber substrate 2 on which the piezoelectric element 40 is formed.
This is a step of forming the cavity 21 by etching the other surface of the “0”. The space in the cavity 21 is etched from the side opposite to the surface on which the piezoelectric element 40 is formed, using anisotropic etching using an active gas such as anisotropic etching or parallel plate reactive ion etching. The portion left without being etched becomes the side wall 22.

Nozzle plate bonding step (FIG. 5C):
The nozzle plate bonding step is a step of bonding the nozzle plate 10 to the etched silicon substrate 20 with an adhesive. When bonding, the nozzle holes 11 are aligned so as to be arranged in the spaces of the cavities 21. The pressure chamber substrate 20 to which the nozzle plate 10 is attached is attached to the housing 25 (see FIG. 3), and the ink jet recording head 1
To complete. When the nozzle plate and the pressure chamber substrate are integrally formed by etching, the step of bonding the nozzle plates is unnecessary. That is, the pressure chamber substrate is etched into a shape that combines the nozzle plate and the pressure chamber substrate, and finally a nozzle hole is provided at a position corresponding to the cavity.

(Example) An example of the above embodiment will be described below. FIG. 6 is a diagram showing how the ratio of the crystal axis having the <001> orientation to the crystal axis having the <111> orientation and the <001> orientation changes depending on the degreasing temperature. As can be seen from FIG. 6, the degreasing temperature and the orientation are closely related.
> The orientation increases. Therefore, it is understood that it is preferable to perform degreasing at a degreasing temperature of 400 ° C. or more in manufacturing the first layer 41.

FIG. 7 is a diagram showing how the abundance of <001> oriented crystal axes changes depending on the amount of the solvent of the high molecular weight organic material when the degreasing temperature is set to 400 ° C. As can be seen from FIG. 7, the abundance of the <001> -oriented crystal axes changes significantly when the solvent for the high molecular weight organic material is not present and when it is present in a small amount. Therefore, it can be seen that a piezoelectric thin film crystallized without using a solvent of a high-molecular organic material like the first layer 41 of the present embodiment has many <001> -oriented crystal axes.

Table 2 shows the relationship between the type of the solvent and the thickness at which cracks occur for the first time in the degreasing step. Dipropylene glycol has a molecular weight of 131;
This is the value when degreased at 0 ° C. From Table 2, it can be seen that the molecular weight is 40
It turns out that the amount of the high molecular organic material of 0 to 600 is suitable as a solvent from the viewpoint of both crack generation and handling.

[0059]

[Table 2]

Table 3 shows the relationship between the degreasing temperature and the thickness at which cracks first occurred in the degreasing step when polyethylene glycol having a molecular weight of 400 to 600 was used. From Table 3,
It can be seen that when polyethylene glycol having a molecular weight of 400 to 600 is used as a solvent, the thickest film can be formed at a degreasing temperature of 400 ° C. Therefore, it can be understood that the degreasing temperature is preferably set to 400 ° C. also in the present embodiment.

[0061]

[Table 3]

As described above, according to the present embodiment, the first layer containing a large number of <001> -oriented crystal axes is formed by crystallizing from a precursor that does not use a high-molecular organic material as a solvent. Since the second layer is formed using one layer as a seed, the ratio of <001> orientation can be increased. Therefore, the piezoelectric element manufactured according to the present embodiment exhibits good piezoelectric characteristics.

Since the second layer is made of a polymer organic material, it is possible to increase the thickness without cracks. Therefore, the production yield is good and the production cost can be reduced.

(Other Modifications) The present invention can be applied to various modifications without depending on the above embodiments. For example, although PMN-PZT has been described in the above embodiment, other ferroelectric piezoelectric ceramics can be similarly considered. That is, a first layer containing a large number of <001> -oriented columnar crystals is formed under a predetermined condition using a precursor that does not use a polymer organic material. Then, using the first layer in which a large number of <001> orientations are formed as seeds, a crystal of the second layer is grown using a precursor containing a high-molecular organic material so that the film can be thickened. Since the second layer takes over the crystal state of the first layer, <001> is also applied to the second layer.
The orientation increases. The temperature condition may be determined according to the type of the piezoelectric ceramic.

The piezoelectric element manufactured according to the present invention is not limited to the piezoelectric element of the ink jet recording head described above.
Ferroelectric devices such as nonvolatile semiconductor storage devices, thin film capacitors, pyroelectric detectors, sensors, surface acoustic wave optical waveguides, optical storage devices, spatial light modulators, frequency doublers for diode lasers, dielectrics Body devices, pyroelectric devices,
It can be applied to the manufacture of piezoelectric devices and electro-optical devices. That is, since the piezoelectric element of the present invention has good piezoelectric characteristics, it is suitable for all uses.

[0066]

As described above, according to the manufacturing method of the present invention, the first layer is formed under the condition that the <001> orientation increases,
Since the second layer, which can be made thick, is grown using the crystal of the first layer as a seed, a piezoelectric element having a large ratio of crystal axes of <001> orientation can be manufactured as a whole. Therefore, this piezoelectric element shows preferable piezoelectric characteristics, and an ink jet recording head using this piezoelectric element shows preferable ink ejection characteristics.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a layer structure of a piezoelectric element of the present invention.

FIG. 2 is an exploded perspective view of the ink jet recording head of the present invention.

FIG. 3 is a perspective view and a partial cross-sectional view of an ink jet recording head of the present invention.

FIG. 4 is a cross-sectional view showing a manufacturing process for explaining a method of manufacturing an ink jet recording head of the present invention (part 1).

FIG. 5 is a sectional view showing a manufacturing process for explaining a method of manufacturing the ink jet recording head of the present invention (part 2).

FIG. 6 is a diagram showing a relationship between a degreasing temperature and a ratio occupied by <001> orientation.

FIG. 7 is a graph showing the abundance ratio of crystal axes of <001> orientation with respect to the amount of solvent of a high-molecular organic material at a degreasing temperature of 400 ° C.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Nozzle plate 20 ... Pressure chamber substrate 30 ... Vibration plate 31 ... Insulating film 32 ... Lower electrode 40 ... Piezoelectric element 41 ... Piezoelectric thin film layer (first layer) 42 ... Piezoelectric thin film layer (second layer) 43 ... Upper electrode 44: Crystal grain 21: Cavity

Claims (17)

[Claims] 1. A piezoelectric element comprising a piezoelectric thin film sandwiched between a lower electrode and an upper electrode, wherein the piezoelectric thin film is formed on the lower electrode and has a first layer having a low microcrystalline grain density; A second layer formed on the first layer and having a high microcrystalline grain density. 2. The microcrystalline grain density of the first layer is 1 × 10
The piezoelectric element according to claim 1, wherein the piezoelectric element is set to ⁶ / cm ² or less. 3. The fine crystal grain density of the second layer is 1 × 10
The piezoelectric element according to claim 1, wherein the piezoelectric element is set to ⁸ / cm ² or more. 4. The piezoelectric element according to claim 1, wherein the piezoelectric thin film has a larger ratio of <001> -oriented and <100> -oriented crystal axes than <111> -oriented crystal axes. 5. The method according to claim 1, wherein the first layer has a thickness of 0.05 μm or more.
2. The piezoelectric element according to claim 1, which is formed with a thickness of 4 μm or less. 6. The piezoelectric thin film has a total thickness of 1.0 μm.
The piezoelectric element according to claim 1, wherein the piezoelectric element has a thickness of at least m. 7. The metal alkoxide forming the piezoelectric thin film may be a lead zirconate titanate (Pb (Zr, Tr)
i) O ₃ : PZT), lead lanthanum titanate ((Pb, L
a) TiO ₃ ), lead lanthanum zirconate titanate ((Pb, La) (Zr, Ti) O ₃ : PLZT) or lead zirconate titanate magnesium niobate (P
b (Mg, Nb) (Zr, Ti) O ₃ : PMN-PZ
2. The piezoelectric element according to claim 1, comprising any one of the piezoelectric ceramics of T). 8. An ink jet recording head comprising the piezoelectric element according to claim 1, wherein a pressure chamber substrate in which a pressure chamber is formed, and a vibration plate that closes one surface of the pressure chamber. An ink jet recording head, comprising: a piezoelectric element provided at a position of the vibration plate corresponding to the pressure chamber, and configured to be able to change the volume of the pressure chamber. . 9. A method of manufacturing a piezoelectric element in which a piezoelectric thin film exhibiting an electromechanical conversion action is sandwiched between a lower electrode and an upper electrode, wherein a piezoelectric ceramic material is formed of a polymer organic material on the lower electrode. Forming a first layer using a metal alkoxide solution produced by dissolving in a solvent other than the above, and a metal alkoxide produced by dissolving a piezoelectric ceramic material in a solvent of a polymer organic material on the first layer Forming a second layer by using a solution to form the piezoelectric thin film. 10. The step of forming the first layer and the step of forming the second layer each include: a) a step of applying a sol, which is the metal alkoxide solution, to a constant thickness; The method for producing a piezoelectric element according to claim 9, further comprising a step of heating and drying and degreasing the sol under a constant atmosphere. 11. The method according to claim 10, wherein, in the step of forming the first layer, the first layer is formed with a thickness of 0.05 μm or more and 0.4 μm or less. 12. The method for manufacturing a piezoelectric element according to claim 10, wherein in the step of forming the first layer, the degreasing temperature is set to a temperature of not less than 430 ° C. and not more than 500 ° C. to perform degreasing. 13. The method according to claim 1, wherein in the step of forming the second layer, polyethylene glycol having a molecular weight of 400 or more and 600 or less is used as a solvent of the metal alkoxide solution.
0. The method for manufacturing a piezoelectric element according to item 0. 14. The method according to claim 10, wherein, in the step of forming the second layer, the degreasing is performed at a temperature of 375 ° C. or more and 425 ° C. or less. 15. The method according to claim 10, wherein, in the step of forming the second layer, the degreasing temperature is set to 400 ° C. to perform degreasing. 16. The metal alkoxide solution includes lead zirconate titanate (Pb (Zr, Ti) O ₃ : P
ZT), lanthanum lead titanate ((Pb, La) Ti
O ₃ ), lanthanum lead zirconate titanate ((Pb,
La) (Zr, Ti) O ₃ : PLZT) or lead magnesium zirconate titanate niobate (Pb (Mg,
_{Nb) (Zr, Ti) O} 3: PMN-PZT) method for producing a piezoelectric element according to claim 10 which comprises using a solution containing either of the piezoelectric ceramics of. 17. A method for manufacturing an ink jet recording head including a piezoelectric element manufactured by the manufacturing method according to claim 9, wherein a vibration plate is formed on one surface of the substrate. A step of manufacturing the piezoelectric element on the vibration plate; and a step of forming the pressure chamber by etching the substrate so that the vibration plate provided with the piezoelectric element forms one surface of the pressure chamber. And a method of manufacturing an ink jet recording head comprising: