JPH11204849A - Piezo-electric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an actuator that can prevent lead diffusion to a board in sintering lead type piezo-electric ceramic material, on the Si board and also has mechanical strength and high reliability. SOLUTION: An electric-mechanical converting element made of a piezo-electric material layer showing an electric-mechanical converting effect between an upper and lower electrode and the electrodes is mounted on a Si board. For an actuator to deform a part of the base 1 according to a given electrical signal, a middle layer 2 having more than one layer is formed between the electric-mechanical converting element. And the middle layer 2 is formed by a mono layer or plural layers composing of a function layer 2a touched with the base 1, an anti-reactive function layer 2b, and a film stress reductive function 2c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a piezoelectric element formed on a Si substrate and a piezoelectric actuator using the piezoelectric element.

[0002]

2. Description of the Related Art As an application of a piezoelectric / electrostrictive element, there is a piezoelectric ink jet head which applies a pressure to a pressurizing chamber to discharge ink droplets. In recent years, high integration of inkjet heads has been demanded, and etching technology has been established by semiconductor processes and micromachining technology, and
An actuator configuration for forming a pressure chamber on a low-cost Si substrate has been devised.

In the ink jet head disclosed in Japanese Patent Application Laid-Open No. 8-252914, an SiO ₂ film is formed on a single-crystal Si substrate, an elastic film and a piezoelectric / electrostrictive layer are laminated, and ink is applied to the Si substrate by anisotropic etching. A configuration and a manufacturing method have been proposed in which a pressurized chamber for discharging droplets is formed, and the SiO ₂ film immediately below the piezoelectric film is removed by BHF, so that the influence of mutual diffusion between the piezoelectric film and the Si substrate can be ignored.

Japanese Patent Application No. 9-107296 discloses a single crystal S
There has been proposed an ink jet head configuration in which a dense lead diffusion preventing film such as a partially or completely stabilized zirconia oxide film or a cerium oxide film is formed on an i-substrate, and Si under the piezoelectric film is left.

[0005]

For the piezoelectric material layer of the electromechanical transducer, lead-based piezoelectric ceramic materials such as lead zirconate titanate (PZT) are often used. But,
For example, if PZT is formed on a Si substrate and then annealing is performed at a high temperature for sintering, lead diffuses on the Si substrate, and melting of SiO ₂ formed on the surface of the Si substrate due to a melting point drop occurs. Occur.

Japanese Patent Application Laid-Open No. 8-252914 discloses an invention which solves the above problem by completely removing the Si substrate and the SiO ₂ film immediately below the piezoelectric film by etching or the like to form an ink pressurizing chamber. However, in the present invention, there is a problem that mechanical strength is weakened because pressure is applied only by the elastic film and the electrode film.

In Japanese Patent Application No. 9-107296, an intermediate layer composed of a zirconia oxide film, a cerium oxide film, or the like, which is a dense portion for preventing lead diffusion or a fully stabilized film, is used for forming an electromechanical conversion element and a pressure chamber substrate. In this invention, the mechanical strength required for the diaphragm and the distortion of the electro-mechanical converter can be effectively transmitted by forming the thin section of the pressurizing chamber portion to have a thickness of 1 to 20 μm. Is disclosed. But,
In order to prevent lead diffusion, for example, when the intermediate layer is formed of a dense single layer having good crystallinity such as an epitaxial film, a perfect single crystal film having no defects and no pinholes has a thickness of 0.1 μm.
Although it is possible to do so, film defects such as pinholes and crystal defects occur, and lead diffusion from these to the Si substrate proceeds. On the other hand, when a dense film capable of preventing the diffusion of lead is formed as a single layer or a plurality of layers, cracks progress from the film surface due to heat history such as firing of the piezoelectric element, and lead diffusion to the Si substrate occurs. Furthermore, there is a problem that the deflection of the Si diaphragm due to the film stress occurs, it becomes difficult to stably eject ink droplets, and there is a variation in each bit.

According to the present invention, a highly reliable intermediate layer having a sufficient mechanical strength is formed from a single layer or a plurality of layers having an adhesion function layer to a substrate, a reaction prevention function layer, and a film stress relaxation function layer. It is a main object of the present invention to provide a piezoelectric actuator formed using the same and an electromechanical transducer.
A second aspect of the present invention is to provide an alignment film made of a metal oxide or a single crystal thin film epitaxially grown on a substrate, and to dispose a substrate adhesion functional layer having a large adhesive force so as to have high mechanical strength. The purpose is to form an intermediate layer.

According to the third aspect of the present invention, a dense metal oxide film having good crystallinity is used as the reaction preventing functional layer.
An object of the present invention is to form an intermediate layer having a high reaction preventing effect between a piezoelectric material layer and a substrate. According to a fourth aspect of the present invention, the stress of the entire intermediate layer is reduced by disposing a film stress relieving layer for canceling or relieving a film stress generated by forming a dense reaction preventing film and an adhesion function film at a high temperature. The purpose is to:

A fifth object of the present invention is to form an intermediate layer having higher toughness and mechanical strength by using a partially or completely stabilized zirconium oxide film as an intermediate layer material. A sixth object of the present invention is to form an intermediate layer more efficiently by using sputtering for forming the intermediate layer.

[0011]

According to a first aspect of the present invention, there is provided a base material comprising upper and lower electrodes and a piezoelectric material layer sandwiched between the electrodes and exhibiting an electromechanical conversion effect. An electro-mechanical conversion element for deforming a part of the base is provided, and one or more intermediate layers are formed between the base and the electro-mechanical conversion element. The piezoelectric actuator includes a single layer or a plurality of layers having an adhesion function layer, a reaction prevention function layer, and a film stress relaxation function layer.

According to a second aspect of the present invention, in the piezoelectric actuator according to the first aspect, the thickness of the contact function layer is 1 μm.
m or less, preferably 0.1 μm or less,
The piezoelectric actuator is a single-crystal thin film epitaxially grown on an alignment film or a substrate.

According to a third aspect of the present invention, in the piezoelectric actuator according to the first aspect, the reaction preventing functional layer is a metal oxide film having a thickness of 2 μm or less, preferably 0.2 μm or less per layer, which is determined by XRD diffraction. Crystallite size 50
This is a piezoelectric actuator made of a crystalline film having a thickness of nm or more.

According to a fourth aspect of the present invention, in the piezoelectric actuator according to the first aspect, the film stress relaxation function layer is a metal oxide film having a thickness of 10 μm or less, preferably 1 μm or less per layer, and is made of a porous or amorphous material. It is a piezoelectric actuator made of quality.

According to a fifth aspect of the present invention, there is provided the piezoelectric actuator according to any one of the first to fourth aspects, wherein the intermediate layer contains at least one oxide of yttrium, cerium, magnesium, and calcium. This is a piezoelectric actuator that is a stabilized zirconium oxide film.

According to a sixth aspect of the present invention, there is provided a method of forming an intermediate layer of a piezoelectric actuator, wherein the zirconium oxide film according to the fifth aspect is formed by sputtering.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic diagram of a piezoelectric element unit to which the present invention can be applied. A piezoelectric material layer 4 exhibiting an electromechanical conversion effect is formed between the intermediate layer 2 and the upper and lower electrodes 3a and 3b on the base 1, and a part of the base is deformed by the application of an electric field. Further, as shown in FIG. 2, when a pressure chamber 5 is formed in a part of the substrate 1 corresponding to the piezoelectric element and the nozzle plate 6 is bonded, the nozzle 7 is applied by applying an electric field to the electrode.
An ink jet piezoelectric head from which the ink in the pressure chamber is ejected from is formed.

The substrate 1 is not particularly limited as long as it is excellent in workability, has high mechanical strength, and is inert at the heat treatment and firing temperatures. , A metal, or a structure made of a plurality of materials.

The electrode material may be any conductor that can withstand a high-temperature oxidizing atmosphere at a heat treatment / sintering temperature, and may be made of a high-melting-point noble metal such as platinum or a platinum group element (Pd, Rh, Ir, Ru), or an alloy thereof. The electrode material as a main component is most preferable from the viewpoint of stability.

PZT is applied to the piezoelectric material layer 4 on the lower electrode layer.
A system ceramic is preferable, and a film thickness of 10 to 20 μm can be formed by a single printing process using a screen printing method. After drying, it is fired in the air at a temperature of 700 to 1000C.

The intermediate layer 2 is composed of a function layer 2a for adhering to the substrate 1, a reaction preventing function layer 2b, and a film stress relieving function layer 2c. In order to enhance the reaction prevention effect, a reaction prevention function layer 2
b and a plurality of film stress relaxation function layers 2c may be laminated as shown in FIG. 3, and each reaction prevention function layer and film stress relaxation function layer is formed of a plurality of films having the same function. It may be configured. The adhesion function layer 2a is desirably a dense and highly adhesive film formed by sputtering, CVD, or the like from the viewpoint of mechanical strength. The film thickness is preferably about 1 μm, and more preferably 0.1 μm or less in order not to cause stress distribution in the film. Therefore, the thickness of the adhesion function layer of the present invention is a metal oxide film having a thickness of 1 μm or less, preferably 0.1 μm or less, and is a single crystal thin film epitaxially grown on an alignment film or a substrate.

The reaction prevention function layer 2b is preferably a dense film formed by sputtering, CVD or the like in order to prevent lead diffusion from PZT constituting the electro-mechanical conversion layer. The film thickness is also about 1 μm, more preferably 0.1 μm.
m or less. Therefore, the thickness of the adhesion function layer of the present invention is a metal oxide film having a thickness of 1 μm or less, preferably 0.1 μm or less, and is a single crystal thin film epitaxially grown on an alignment film or a substrate. The film stress relaxation function layer 2c is formed of a porous or amorphous film that cancels or absorbs the stress generated in the dense film. 10μ by sputtering, CVD, sol-gel method and printing method
m, but the mechanical strength, productivity,
From the characteristics of the actuator, it is preferable to form a film with a thickness of 1 μm or less by sputtering or CVD. For this reason, the reaction preventing functional layer of the present invention is a metal oxide film having a thickness of 2 μm or less, preferably 0.2 μm or less per layer, and is composed of a crystal film having a crystallite size of 50 nm or more determined by XRD diffraction.
The intermediate layer material is a metal oxide film having sufficient resistance at the PZT firing temperature, low reactivity with lead, and high mechanical strength, for example, MgO, GeO ₂ , Y ₂ O ₃ , Al ₂
Use of a partially or fully stabilized zirconium oxide film containing at least one oxide of O ₃ , SrTiO ₃ , MgO—Al ₂ O ₃ or yttrium, cerium, magnesium, or calcium having higher toughness Is also preferred. Further, as shown in Examples described later, it is desirable that all the functional films constituting the intermediate layer are formed from the same material by a common film forming method such as sputtering from the viewpoint of productivity.

Example 1 A substrate temperature (850, 650, 500, 150) was introduced on a Si (100) substrate by RF magnetron sputtering while introducing oxygen and argon.
C.) to obtain a zirconium oxide (8 mol% Y ₂ O ₃ —ZrO ₂ ) film stabilized with yttrium (hereinafter referred to as YS).
Z) was deposited to a thickness of 1000 °. Table 1 shows the results obtained by measuring the substrate adhesion of each film using a peeling method. The higher the substrate temperature at the time of film formation, the better the crystallinity of the YSZ film, and accordingly the adhesive force was also improved. For example, when a movable part is required to have mechanical strength that can withstand driving at a high frequency, such as an ink jet head, a film having good crystallinity and a high adhesive strength such as a single crystal thin film epitaxially grown on an alignment film or a substrate is required. preferable.

[0024]

[Table 1]

Example 2 In order to investigate the correlation between the crystallinity of the reaction-preventing film and the reactivity with lead, cerium oxide was introduced onto a Si wafer (100) using RF magnetron sputtering while introducing oxygen and argon. A film of zirconium oxide (40 mol% CeO ₂ -ZrO ₂ ), which was stabilized by, was formed (substrate temperature: 850, 650, 500, 150 ° C.). A PbO paste was printed on the produced CeO ₂ -ZrO ₂ / Si film and heated at 900 ° C. for 2 hours, and then the lead diffusion in the depth direction was measured using SIMS. FIG. 4 shows the results. As a result, when the film was formed at 800 ° C., the lead diffusion depth was the smallest at about 400 °, the film formation temperature was higher, and the higher the crystallinity (evaluated by the XRD: RC method), the higher the reaction prevention effect was obtained. .

(Embodiment 3) Next, in order to examine the effect of the film stress relaxation function layer, first, a 4-inch Si wafer (10
0), YSZ (8 ol% Y ₂ O ₃ -Z) was formed by sputtering under a film forming condition of a substrate temperature of 850 ° C. and a pressure of 1 × 10 ⁻¹ Pa.
(rO ₂ ) film is epitaxially grown to a thickness of 0.1 μm. While introducing oxygen, argon, and nitrogen thereon, the substrate temperature was reduced to 7.
50 ° C., pressure 2 Pa (Ar: O ₂ : N ₂ = 8: 1: 1)
Then, a porous YSZ film is formed by changing the film thickness. Further, a dense YSZ film having a thickness of 0.2 μm was formed thereon under the conditions of a substrate temperature of 850 ° C. and a pressure of 1 × 10 ⁻⁵ Pa. YS
FIG. 5 shows the results obtained by measuring the radius of curvature (the amount of deflection of the substrate) of the Si wafer on which the Z composite film was laminated by Newton's ring observation and examining the correlation between the film stress relaxation function layer thickness and the film stress relaxation effect. When a porous film stress relaxation function layer is not used, Y
The compressive stress acting on the SZ composite film was alleviated by forming the film stress relaxation function layer therebetween, and the substrate deflection of the Si wafer was reduced. Considering the mechanical strength of the intermediate layer, the thickness of the film stress relaxation functional layer per layer is 1 μm.
m or less.

Example 4 Single-crystal Si described in Example 3
In the YSZ film laminated on the substrate, a platinum paste is screen-printed on an intermediate layer / Si substrate having a film stress relaxation function layer of 0.5 μm to form a lower electrode 3a of 5 μm. Subsequently, 0.5 Pb (N
i _1/3 Nb _2/3 ) O ₃ -0.5 Pb (Zr _0.7 Ti _0.3 ) O ₃
(Hereinafter abbreviated as PNN-PZT) by screen printing,
It is dried at 150 ° C. for 30 minutes, and then fired at 900 ° C. for 2 hours in air in a firing furnace. PNN-PZT
After baking, the upper electrode 3b is formed by baking silver-palladium by screen printing, and a PNN-PZT capacitor similar to the piezoelectric actuator configuration shown in FIG. 1 is manufactured. In addition, a similar capacitor was used for a YSZ (Ceraflex A) substrate manufactured by Nippon Fine Ceramics Co., Ltd.
μm), and the relative dielectric constants were measured and compared. As a result, the PZT formed on the YSZ intermediate layer / Si
However, no lead diffusion into the Si substrate was observed, and the relative dielectric constant (εr = 200) substantially equal to that of PZT formed on the YSZ substrate.
0) was obtained. This means that a thick film PNN-PZT exhibiting good piezoelectric characteristics was formed on the Si substrate.

(Embodiment 5) When sputtering is used to form an intermediate layer, an epitaxial film, an alignment film, an amorphous film, and a porous film can be easily formed by simply changing the substrate temperature, gas pressure, and gas value with the same target. Can be formed. As shown in Embodiment 3, it is possible to continuously form each functional layer by a combination of these, and a sputter deposition is preferable from the viewpoint of manufacturing efficiency.

[0029]

According to the first aspect of the present invention, in a piezoelectric actuator to which the present invention can be applied, a single layer having an adhesion function, a reaction prevention function, and a film stress relaxation function is formed by bonding an intermediate layer between a substrate and an electro-mechanical conversion layer. By configuring in multiple layers,
Lead diffusion from the electro-mechanical conversion layer is prevented, the adhesion to the substrate is strong, and the compressive stress of the intermediate layer can be reduced, whereby a highly reliable and high-performance piezoelectric actuator can be provided.

According to the second aspect of the present invention, a piezoelectric actuator having a more reliable intermediate layer can be realized by forming a dense substrate adhesion layer having high mechanical strength.

According to a third aspect of the present invention, an actuator having a highly reliable intermediate layer having a high reaction preventing effect between the piezoelectric material layer and the substrate can be realized by forming a dense reaction preventing functional layer. Can be.

According to the fourth aspect, by forming a film stress relaxation function layer made of porous or amorphous,
It is possible to reduce the film stress of the entire intermediate layer and to realize an actuator having a more reliable intermediate layer.

According to a fifth aspect of the present invention, the intermediate layer is made of stabilized or partially stabilized zirconium oxide to provide an intermediate layer having high mechanical strength, high toughness, high reliability and high performance. An actuator can be realized.

According to the sixth aspect, by forming a zirconium oxide film as an intermediate layer by sputtering, an intermediate layer having high reliability and low cost can be manufactured.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a piezoelectric element unit to which the present invention can be applied.

FIG. 2 is a view schematically showing an inkjet piezoelectric head using the piezoelectric element unit of the present invention.

FIG. 3 is a view similar to FIG. 1, showing another embodiment of the piezoelectric element unit.

FIG. 4 is a diagram showing a correlation between a film formation temperature of a substrate and a lead diffusion depth.

FIG. 5 is a diagram showing a correlation between a film thickness of a film stress relaxation function layer and a film stress relaxation effect.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Intermediate layer, 2a ... Adhesion function layer, 2b ... Reaction prevention function layer, 2c ... Film stress relaxation function layer, 3 ... Electrode, 3a
... lower electrode, 3b ... upper electrode, 4 ... piezoelectric material layer, 5 ... pressure chamber, 6 ... nozzle plate, 7 ... nozzle.

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H01L 41/22 (72) Inventor Kunihiro Yamanaka 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company, Ltd.

Claims (6)

[Claims] A piezoelectric material layer having an electromechanical conversion effect sandwiched between upper and lower electrodes and said electrodes on a substrate,
An electro-mechanical conversion element portion that deforms a part of the base in accordance with an applied electric signal is arranged, and a piezoelectric actuator in which one or more intermediate layers are formed between the base and the electro-mechanical conversion element portion, A piezoelectric actuator, characterized in that the intermediate layer comprises a single layer or a plurality of layers having a function layer for adhesion to the substrate, a function layer for preventing reaction, and a function layer for reducing film stress. 2. The piezoelectric actuator according to claim 1, wherein the thickness of the adhesion function layer is a metal oxide film of 1 μm or less, preferably 0.1 μm or less, and is a single crystal thin film epitaxially grown on an alignment film or a substrate. A piezoelectric actuator, comprising: 3. The piezoelectric actuator according to claim 1, wherein the reaction prevention function layer is a metal oxide film having a thickness of 2 μm or less, preferably 0.2 μm or less per layer.
A piezoelectric actuator comprising a crystal film having a crystallite size of 50 nm or more determined by D diffraction. 4. The piezoelectric actuator according to claim 1, wherein the film stress relaxation function layer has a thickness of 10 μm per layer.
A piezoelectric actuator, which is a metal oxide film having a thickness of not more than m, preferably not more than 1 μm, and made of porous or amorphous. 5. The piezoelectric actuator according to claim 1, wherein the intermediate layer is made of yttrium,
A piezoelectric actuator comprising a partially or completely stabilized zirconium oxide film containing at least one oxide of cerium, magnesium, and calcium. 6. A method for producing an intermediate layer of a piezoelectric actuator, comprising forming the zirconium oxide film according to claim 5 by sputtering.