JP2004186436A - Piezoelectric/electrostrictive film element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric/electrostrictive film element whose a connecting state can be much more stably obtained. <P>SOLUTION: A lower electrode 4 of a ceramics substrate 1 is continuously formed from the upper part of a thin diaphragm 3 to the upper part of a thick part 2, and an auxiliary electrode 8 is independently formed on the thick part 2 of the ceramic substrate 1. A polarized layer where components included in the ceramic substrate 1 and/or a portion of components included in a connection layer 7 constituted of an insulator formed between the lower electrode 4 and the auxiliary electrode 8 are polarized is formed between the connection layer 7 and the ceramic substrate 1, and a piezoelectric/electrostriction film 5 is formed along them. Thus, the reactivity of the substrate materials and the connection layer materials can be increased, and complete connection whose connecting status is much more stable can be obtained. Therefore, it is possible to increase the durability of elements, to prevent the fluctuation of vibration or secular change, and to continuously obtain suitable elements as an element for discriminating fluid characteristics or liquid/gas according to the detection of electric constants in vibration, an element for measuring a voice pressure, micronic weight, and acceleration or the like and an actuator element. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２４】
基板材料がジルコニアを主成分とし、結合層添加物がＳｉＯ_２の場合は、添加量を調整し偏在層の厚みが１μｍ以上、５μｍ以下であると、３００時間後の素子の故障率を低減することできる。
また、基板材料がジルコニアを主成分とし、結合層添加物がＹ_２Ｏ_３、アルカリ土類金属酸化物であるＣａＯ、希土類金属酸化物であるＬａ_２Ｏ_３の各場合も、添加量０．１ｗｔ％で偏在層の厚みが２μｍであると、３００時間後の素子の故障率は充分に低減されている。
更に、ＳｉＯ_２とＹ_２Ｏ_３とを添加量０．１ｗｔ％ずつ混合した結合層添加物であっても、３００時間後の素子の故障率は充分に低減されている。
また、ＳｉＯ_２、Ｙ_２Ｏ_３、アルカリ土類金属酸化物又は希土類金属酸化物の各添加量がは、酸化物換算で０．０５ｗｔ％から０．３ｗｔ％であることが好ましい。０．０５ｗｔ％より小さい場合は、結合力を向上させる効果が無く、０．３ｗｔ％より多い場合、基板材料や圧電電歪幕材料に変質を引き起こし、素子特性の変化や素子の強度を低下させる。
【００２５】
【発明の効果】
本発明による圧電／電歪膜型素子にあっては、基板材料と結合層材料との反応性が高まり、セラミックス基板と圧電／電歪膜との結合状態がより安定的な完全結合となる。よって、素子としての耐久性が高まり、振動のばらつきや経時変化が無く、振動における電気的定数の検知により流体特性や液体／気体を判別する素子、あるいは音圧や微小重量、加速度等の測定素子、さらにはアクチュエータ素子として、好適な素子が継続的に得られることとなる。
【図面の簡単な説明】
【図１】本発明のセンサ用圧電／電歪膜型素子の実施形態を示す説明図である。
【符号の説明】
１・・セラミックス基板、２・・厚肉部、３・・薄肉ダイヤフラム部、４・・下部電極、５・・圧電／電歪膜、６・・上部電極、７・・結合層、７Ａ・・偏在層、８・・補助電極、９・・貫通孔、１０・・空洞部。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a piezoelectric / electrostrictive film element, and more particularly to a piezoelectric / electrostrictive device used for a microphone or a viscosity sensor, for example, as an actuator utilizing a bending displacement or as a sensor for fluid characteristics, sound pressure, minute weight, acceleration, etc. The present invention relates to a film-type element.
[0002]
[Prior art]
A piezoelectric / electrostrictive film type element has been conventionally used as an actuator or various sensors. As disclosed in Patent Document 1, the applicant sequentially arranges a lower electrode and an auxiliary electrode, a piezoelectric / electrostrictive film, and an upper electrode on a substrate made of ceramics having a thin diaphragm portion having a thick portion at a peripheral portion. A piezoelectric / electrostrictive film type element in which a ceramic substrate and a piezoelectric / electrostrictive film are completely bonded by providing a bonding layer made of an insulator between a lower electrode and an auxiliary electrode. We are developing electrostrictive film type devices.
[0003]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-004135
[Problems to be solved by the invention]
In the manufacturing process of the piezoelectric / electrostrictive film element, the firing conditions had to be strictly controlled in order to make the bonding state of the bonding layer complete. By taking the time and effort of fine adjustment, the initial electric constant is not varied among the individual elements, and the electric constant does not change with time.
[0005]
[Means for Solving the Problems]
Therefore, in order to make the bonding state of the bonding layer more complete, the present invention according to claim 1 has a lower electrode and an auxiliary electrode formed on a substrate made of ceramics having a thin diaphragm portion having a thicker portion at a peripheral portion. A piezoelectric / electrostrictive film and an upper electrode are sequentially laminated, and a bond formed of (Bi _0.5 Na _0.5 ) TiO ₃ or a material mainly containing the same is provided between the lower electrode and the auxiliary electrode. A piezoelectric / electrostrictive film type element provided with a layer,
An uneven distribution layer in which a component contained in the ceramic substrate and / or a part of a component contained in the coupling layer is locally distributed is formed with a thickness of 1 to 5 μm between the ceramic substrate and the bonding layer. This is a piezoelectric / electrostrictive film element.
Thereby, the reactivity with the substrate material and / or the bonding layer material was increased, and the bonding state was more stably obtained, and complete bonding was obtained.
Here, the unevenly distributed layer in which a component contained in the ceramic substrate and / or a part of the component included in the bonding layer is unevenly distributed is defined as a case where a part of the component included in the ceramic substrate is unevenly distributed in the bonding layer. This refers to a case where some of the components contained in the layer are unevenly distributed on the ceramic substrate, and a case where the two cases are formed continuously or in contact with each other.
Further, the thickness of the unevenly distributed layer is preferably 1 μm or more and 5 μm or less. If the thickness is less than 1 μm, a perfect bonding state cannot be obtained between the ceramic substrate and the bonding layer. As a result, the durability of the entire device is low. If the thickness exceeds 5 μm, the piezoelectric film on the bonding layer is adversely affected. This causes the initial device performance to be lost over time.
[0006]
According to a second aspect of the present invention, the ceramic substrate is made of a material containing zirconia as a main component, and the bonding layer is made of (Bi _0.5 Na _0.5 ) TiO ₃ or _2. The piezoelectric / electrode according to claim 1, wherein the piezoelectric / electrode is formed by adding at least one kind selected from the group consisting of SiO ₂ , Y ₂ O ₃ , an alkaline earth metal oxide and a rare earth metal oxide to a material as a component. This is a strained film element.
As a result, SiO ₂ forms a glass component to increase the bonding force, and the addition amount is small, so that it does not adversely affect the ceramic substrate or the piezoelectric / electrostrictive film. On the other hand, since the substrate material is mainly composed of zirconia, components of Y ₂ O ₃ , an alkaline earth metal oxide or a rare earth metal oxide which are easily dissolved in zirconia can increase the bonding force. When the substrate material is alumina, the alkaline earth metal oxide reacts with alumina to form a spinel-type compound to increase the bonding force.
The addition amount of SiO ₂ , Y ₂ O ₃ , alkaline earth metal oxide or rare earth metal oxide is preferably 0.05 wt% to 0.3 wt% in terms of oxide. When the content is less than 0.05 wt%, there is no effect of improving the bonding force, and when the content is more than 0.3 wt%, the material of the substrate or the piezoelectric electrostrictive film is deteriorated, thereby changing the element characteristics and decreasing the element strength. It is because they do.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an embodiment of a piezoelectric / electrostrictive film element according to the present invention in (a) a plane, (b) a vertical section along line AA, and (c) an enlarged view of a coupling layer portion. ing. Such a piezoelectric / electrostrictive film type element has a lower electrode 4, an auxiliary electrode 8, a piezoelectric / electrostrictive film 5, an upper electrode 6 on a ceramic substrate 1 having a thin diaphragm portion 3 and a thicker portion 2. Are formed in an integrated structure which is sequentially laminated by a normal film forming method. Between the lower electrode 4 and the auxiliary electrode 8, the piezoelectric / electrostrictive film 5 and the ceramic substrate 1 are bonded in a completely bonded state by a bonding layer 7 made of an insulator, and between the ceramic substrate 1 and the bonding layer 7. Has a localized layer 7A having a thickness of 1 to 5 μm, in which components contained in the ceramic substrate 1 and / or components contained in the bonding layer 7 are partially distributed.
[0008]
As a material of the ceramic substrate 1, a material having heat resistance, chemical stability, and insulating properties is preferable. This is because the lower electrode 4, the piezoelectric / electrostrictive film 5, and the upper electrode 6 may be heat-treated when integrated, as described later. This is because when sensing liquid, the liquid may have conductivity or corrosiveness.
Examples of ceramics that can be used from this viewpoint include stabilized zirconium oxide, aluminum oxide, magnesium oxide, mullite, aluminum nitride, silicon nitride, and glass. Of these, stabilized zirconium oxide can be suitably used because it can maintain high mechanical strength and is excellent in toughness even when the thin diaphragm portion 3 is formed thin.
[0009]
The thickness of the thin diaphragm portion 3 of the ceramic substrate 1 is generally 50 μm or less, preferably 30 μm or less, more preferably 15 μm or less so as not to hinder the vibration of the piezoelectric / electrostrictive film. In addition, the surface shape of the thin diaphragm portion may be any shape such as a rectangle, square, triangle, ellipse, and true circle. A circle is selected as needed.
[0010]
The lower electrode 4 is formed from one end of the ceramic substrate 1 so as to have a size on the thin diaphragm portion 3 on which the piezoelectric / electrostrictive film 5 is to be formed, but is smaller or larger. It may be formed in a predetermined size. One end of the lower electrode 4 is used as a lead terminal. On the other hand, the auxiliary electrode 8 extends from the end of the ceramic substrate 1 opposite to the lower electrode 4 to a predetermined position above the thin diaphragm 3. One end of the auxiliary electrode 8 is used as a lead terminal.
[0011]
The lower electrode 4 and the auxiliary electrode 8 may be different materials or the same material, and a conductive material having good bonding properties to both the ceramic substrate 1 and the piezoelectric / electrostrictive film 5 is used. Specifically, an electrode material containing platinum, palladium, rhodium, silver, or an alloy thereof as a main component is preferably used. In particular, when forming a piezoelectric / electrostrictive film, heat treatment for sintering is performed. In this case, platinum and an alloy containing the same as a main component are preferably used.
[0012]
Various known film forming techniques are used for forming the lower electrode 4 and the auxiliary electrode 8. Specifically, a thin film forming technique such as ion beam, sputtering, vacuum deposition, CVD, ion plating, and plating, and a thick film forming technique such as screen printing, spraying, and dipping are appropriately selected. Method and screen printing method are suitably selected.
[0013]
Prior to the formation of the piezoelectric / electrostrictive film 5, a coupling layer 7 made of an insulator for forming a complete coupling state is formed between the lower electrode 4 and the auxiliary electrode 8. As the bonding layer 7 made of an insulator, (Bi _0.5 Na _0.5 ) TiO ₃ or a material containing this as a main component, for example, (1-x) (Bi _0.5 Na _0.5 ) TiO ₃ − At least one selected from SiO ₂ , Y ₂ O ₃ , alkaline earth metal oxide or rare earth metal oxide is added to xKNbO ₃ (x is 0.08 ≦ x ≦ 0.5 in mole fraction) or the like. Preferred materials are preferred. In the case of these systems, it is preferable to use a composition in which Na or K is smaller than the stoichiometric composition in order to prevent Na and K from being released and impairing the insulating property of the film. For example, it is preferable that the molar ratio satisfies 1.01 ≦ Bi / Na ≦ 1.08 and 0.92 ≦ (Bi + Na) /Ti≦0.98. Further, by being in this range, generation of a different phase of the piezoelectric film can be suppressed, and the particle size can be set to be optimal for expressing the characteristics of the element.
The bonding layer 7 is made of bismuth oxide sodium hydrogen tartrate, titanium oxide and potassium niobium oxide tartrate, and oxides and carbonates of additive components are weighed so as to have a predetermined composition of the bonding layer. Using a 2φ zirconia cobblestone, they were mixed in a ball mill for 16 hours. The obtained slurry was dried, calcined in the air at 900 ° C. for 2 hours, and further pulverized in ethanol with a ball mill using 2φ zirconia balls. The pulverization time is selected so that the specific surface area of the powder after pulverization is 5 to 10 m ² / g. Here, if it is less than 5 m ² / g, the activity of the powder is low, so that the reaction with zirconia does not proceed and the uneven distribution layer is not formed. If it is more than 10 m ² / g, the activity is too high and the powders agglomerate, so that the uneven distribution layer cannot be formed uniformly.
The obtained powder is prepared by using polyvinyl butyral or ethyl cellulose as a binder component, adding terpineol or butyl carbitol as a solvent, and kneading with a triroll mill to obtain a printing paste.
[0014]
Further, the piezoelectric / electrostrictive film 5 is made of (Bi _0.5 Na _0.5 ) TiO ₃ described later or a material containing this as a main component, or (1-x) (Bi _0.5 Na _0.5 ) TiO 3. _3- xKNbO ₃ (x is 0 ≦ x ≦ 0.06 in mole fraction) or (1-x) (Bi _0.5 Na _0.5 ) when composed of a material containing this as a main component. The bonding layer 7 made of a material mainly composed of TiO ₃ -xKNbO ₃ (x is 0.08 ≦ x ≦ 0.5 in a mole fraction) is used as a bonding layer for both the piezoelectric / electrostrictive film 5 and the ceramic substrate 1. Is more preferably used since it has high adhesion and can suppress adverse effects on the piezoelectric / electrostrictive film 5 and the ceramic substrate 1 during heat treatment. That is, the bonding layer _{7 (1-x) (Bi} 0.5 Na 0.5) TiO 3 -xKNbO 3 (x is 0.08 ≦ x ≦ 0.5 in mole fraction) With the piezoelectric / Since it has the same components as the electrostrictive film 5, the adhesion to the piezoelectric / electrostrictive film 5 is enhanced. In addition, there is little problem due to the diffusion of a different element which is likely to occur when glass is used, and since it contains a large amount of KNbO ₃ , it has high reactivity with a ceramic substrate and can be firmly bonded. Further, (1-x) (Bi _0.5 Na _0.5 ) TiO ₃ —xKNbO ₃ (x is a mole fraction of 0.08 ≦ x ≦ 0.5) has almost no piezoelectric characteristics, and is used. Oscillation, displacement and stress are not generated with respect to the electric field generated at the time of the lower electrode 4 and the auxiliary electrode 8, so that stable element characteristics can be obtained.
[0015]
An ordinary thick film method is used for forming these bonding layers 7, and particularly, a stamping method, a screen printing method, or an ink jet method when the size of a portion to be formed is about several tens μm to several hundred μm. It is preferably used. When heat treatment of the bonding layer 7 is necessary, the heat treatment may be performed before the next piezoelectric / electrostrictive film 5 is formed, or may be simultaneously performed after the formation of the piezoelectric / electrostrictive film 5.
[0016]
The piezoelectric / electrostrictive film 5 is formed so as to straddle the lower electrode 4, the auxiliary electrode 8 and the coupling layer 7, and to have a size to cover the lower electrode 4. As the material for the piezoelectric / electrostrictive film, any material may be used as long as it exhibits a piezoelectric / electrostrictive effect. Such materials include lead zirconate, lead titanate, and lead zirconate titanate (PZT). Lead-based ceramic piezoelectric / electrostrictive materials, barium titanate and ferroelectric ceramics containing titanium as a main component, polymer piezoelectrics represented by polyvinylidene fluoride (PVDF), or (Bi _{. 5} Na _0.5 ) TiO ₃ , a Bi-based ceramic piezoelectric material, and a Bi layered ceramic. Of course, it is needless to say that a mixture of these, a solid solution having improved piezoelectric / electrostrictive characteristics, and a material to which an additive is added can be used. The PZT-based piezoelectric material has high piezoelectric characteristics and is suitably used as a material for a sensor capable of high-sensitivity detection. Further, in particular, it is preferable that the ceramic substrate be made of a material mainly containing at least one selected from the group consisting of lead titanate, lead zirconate, lead magnesium niobate and lead nickel niobate. It is more preferably used because it has low reactivity, is unlikely to cause segregation of components during heat treatment, can be favorably treated to maintain the composition, and can easily obtain the desired composition and crystal structure.
[0017]
Further, when platinum or an alloy containing platinum as a main component is used for the lower electrode 4 and the auxiliary electrode 8, the bondability with the platinum and the alloy is reduced, the characteristic variation of the element is reduced, and high reliability is obtained. Therefore, (Bi _0.5 Na _0.5 ) TiO ₃ or a material containing this as a main component is preferably used as the piezoelectric / electrostrictive material. Among these, in _particular, is a material to be _{(1-x) (Bi 0.5} Na 0.5) TiO 3 -xKNbO 3 (x is 0 ≦ x ≦ 0.06 in molar fraction) or mainly of this Since it has relatively high piezoelectric characteristics, it is more preferably used.
[0018]
Such a piezoelectric / electrostrictive material is formed as the piezoelectric / electrostrictive film 5 by a known various film forming method similarly to the lower electrode 4 and the auxiliary electrode 8. Among them, screen printing is preferably used from the viewpoint of low cost.
[0019]
The thus formed piezoelectric / electrostrictive film 5 is heat-treated as necessary, and is integrated with the lower electrode 4, the auxiliary electrode 8, and the coupling layer 7. In the present invention, it is necessary to strengthen the bonding properties between the piezoelectric / electrostrictive film 5, the lower electrode 4, the auxiliary electrode 8, and the coupling layer 7 in order to suppress the characteristic variation of the element and increase the reliability. Therefore, (Bi _0.5 Na _0.5 ) TiO ₃ or a material containing this as a main component, in particular, (1-x) (Bi _0.5 Na _0.5 ) TiO ₃ -xKNbO ₃ (x is a mole fraction) It is preferable that a heat treatment is performed at a temperature of 900 ° C. to 1400 ° C., preferably 1000 ° C. to 1300 ° C. using a material having a ratio of 0 ≦ x ≦ 0.06) or a main component thereof. The same applies to the case where a PZT-based material is used. At this time, it is preferable to perform the heat treatment while controlling the atmosphere together with the evaporation source of the piezoelectric / electrostrictive material so that the piezoelectric / electrostrictive film 5 does not become unstable at a high temperature.
After the heat treatment, the unevenly distributed layer 7A, in which the components contained in the ceramic substrate 1 and / or the components included in the bonding layer 7 are partially unevenly distributed, is formed between the ceramic substrate 1 and the bonding layer 7 as shown in FIG. ) Can be formed with a thickness of 1 to 5 μm.
[0020]
Further, on the piezoelectric / electrostrictive film 5 thus formed, the upper electrode 6 is continuously formed from the piezoelectric / electrostrictive film 5 to the auxiliary electrode 8. Note that the size of the upper electrode 6 may be larger than the lower electrode 4 and the auxiliary electrode 8, or may be the same size or smaller.
As a material of the upper electrode 6, a conductive material having a high bonding property with the piezoelectric / electrostrictive film 5 is used, and is formed by the same film forming method as the lower electrode 4 and the auxiliary electrode 8.
Further, the upper electrode 6 is heat-treated as necessary after the film is formed, and is joined to the piezoelectric / electrostrictive film 5 and the auxiliary electrode 8 to form an integral structure. As in the case of the lower electrode 4, such a heat treatment is not necessarily required.
[0021]
When the lower electrode 4, the bonding layer 7, the piezoelectric / electrostrictive film 5, and the upper electrode 6 are joined by heat treatment, they may be heat-treated each time they are formed, or they may be formed sequentially and then simultaneously. Heat treatment may be performed. When performing the heat treatment, it is needless to say that the heat treatment temperature is appropriately selected in order to suppress the deterioration due to the good bonding property and the diffusion of the constituent elements. Although the lower electrode 4 and the like are laminated on the fired ceramic substrate 1, the lower electrode 4 and the bonding layer 7 and the like may be laminated and fired on the ceramic substrate 1 before firing. As a result, the case where some of the components contained in the ceramic substrate are unevenly distributed in the bonding layer and the case where some of the components contained in the bonding layer are unevenly distributed in the ceramic substrate are continuously or in contact with each other. Thus, the unevenly distributed layer can be formed.
Further, in FIG. 1, the through hole 9 is formed in the cavity 10, but the structure below the cavity 10 in which the element contacts the fluid may be any structure such as a simple cavity structure without a lid, Not limited.
[0022]
【Example】
A sine wave having an offset of +5 V, 10 Vp-p, and a frequency of 1 kHz was applied to the device under environmental conditions of a temperature of 40 ° C. and a humidity of 85%, and the failure rate after 240 hours was measured.
[0023]
[Table 1]

[0024]
When the substrate material is zirconia as a main component and the bonding layer additive is SiO ₂ , the addition amount is adjusted, and if the thickness of the uneven distribution layer is 1 μm or more and 5 μm or less, the failure rate of the element after 300 hours is reduced. I can do it.
Also, in each case where the substrate material is zirconia as a main component, and the additive for the bonding layer is Y ₂ O ₃ , CaO which is an alkaline earth metal oxide, and La ₂ O ₃ which is a rare earth metal oxide, the addition amount is 0. When the thickness of the unevenly distributed layer is 1 μm and the thickness of the uneven distribution layer is 2 μm, the failure rate of the device after 300 hours is sufficiently reduced.
Further, even with a bonding layer additive in which SiO ₂ and Y ₂ O ₃ are added in an amount of 0.1 wt%, the failure rate of the device after 300 hours is sufficiently reduced.
Further, the addition amount of SiO ₂ , Y ₂ O ₃ , alkaline earth metal oxide or rare earth metal oxide is preferably 0.05 wt% to 0.3 wt% in terms of oxide. When the content is less than 0.05 wt%, there is no effect of improving the bonding force, and when the content is more than 0.3 wt%, the material of the substrate or the piezoelectric electrostrictive curtain is deteriorated, and the characteristics of the device are changed and the strength of the device is reduced. .
[0025]
【The invention's effect】
In the piezoelectric / electrostrictive film element according to the present invention, the reactivity between the substrate material and the bonding layer material is increased, and the bonding state between the ceramic substrate and the piezoelectric / electrostrictive film is more stable and complete. Therefore, the durability of the element is increased, there is no variation in vibration and no change with time, and an element for determining a fluid characteristic or a liquid / gas by detecting an electric constant in vibration, or a measuring element for sound pressure, minute weight, acceleration, etc. Further, a suitable element can be continuously obtained as an actuator element.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an embodiment of a piezoelectric / electrostrictive film element for a sensor according to the present invention.
[Explanation of symbols]
1 Ceramic substrate, 2 thick part, 3 thin diaphragm part, 4 lower electrode, 5 piezoelectric / electrostrictive film, 6 upper electrode, 7 bonding layer, 7A Unevenly distributed layer, 8 auxiliary electrodes, 9 through-holes, 10 cavities.

Claims (2)

A lower electrode and an auxiliary electrode, a piezoelectric / electrostrictive film, and an upper electrode are sequentially laminated on a substrate made of ceramics having a thin diaphragm portion having a thicker portion at a peripheral portion. A piezoelectric / electrostrictive film element provided with a bonding layer formed of (Bi _0.5 Na _0.5 ) TiO ₃ or a material containing the same as a main component,
An uneven distribution layer in which a component contained in the ceramic substrate and / or a part of a component contained in the coupling layer is locally distributed is formed with a thickness of 1 to 5 μm between the ceramic substrate and the bonding layer. Piezoelectric / electrostrictive film type element. The ceramic substrate is formed of a material mainly composed of zirconia, and the bonding layer is made of (Bi _0.5 Na _0.5 ) TiO ₃ or a material mainly composed of SiO ₂ , Y _2. O _3, the piezoelectric / electrostrictive film element according to claim 1, wherein the at least one selected from alkaline earth metal oxides or rare earth metal oxide is formed of a material formed by adding.

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