JP3894112B2 - Piezoelectric / electrostrictive membrane element - Google Patents

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ＳｉＯ₂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、ＳｉＯ₂とＹ₂Ｏ_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、ＳｉＯ₂、Ｙ₂Ｏ_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]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric / electrostrictive film type element, and in particular, an actuator that utilizes bending displacement, and a piezoelectric / electrostrictive used in, for example, a microphone or a viscosity sensor as a sensor for fluid characteristics, sound pressure, minute weight, acceleration, etc. The present invention relates to a membrane element.
[0002]
[Prior art]
Piezoelectric / electrostrictive membrane elements have been conventionally used as actuators and various sensors. The applicant, as in Patent Document 1, sequentially forms a lower electrode, an auxiliary electrode, a piezoelectric / electrostrictive film, and an upper electrode on a substrate made of ceramics having a thin diaphragm portion with a thick portion at the periphery. A laminated piezoelectric / electrostrictive film type element, in which a bonding layer made of an insulator is provided between a lower electrode and an auxiliary electrode so that the ceramic substrate and the piezoelectric / electrostrictive film are in a completely coupled state. We are developing electrostrictive membrane elements.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-004135
[Problems to be solved by the invention]
In the process of manufacturing the piezoelectric / electrostrictive film element, it is necessary to strictly control the firing conditions in order to make the bonding state of the bonding layer completely bond. Further, by taking the effort of fine adjustment, there is no variation in the initial electrical constant among the individual elements so that the electrical 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 is directed to a substrate made of ceramics having a thin diaphragm portion having a thick portion at a peripheral portion, a lower electrode and an auxiliary electrode. In addition, the piezoelectric / electrostrictive film and the upper electrode are sequentially laminated, and a bond formed of (Bi _0.5 Na _0.5 ) TiO ₃ or a material containing this as a main component between the lower electrode and the auxiliary electrode. A piezoelectric / electrostrictive film type element provided with a layer,
The ceramic substrate is formed 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 a material containing this as a main component with SiO ₂ , Y ₂ O. _3. While formed of a material formed by adding at least one selected from alkaline earth metal oxides or rare earth metal oxides,
An uneven distribution layer in which a component contained in the ceramic substrate and / or a part of a component contained in the bonding layer is unevenly distributed is formed between the ceramic substrate and the bonding layer with a thickness of 1 to 5 μm. This is a piezoelectric / electrostrictive film type element.
As a result, the reactivity with the substrate material and / or the bonding layer material was increased, and a complete bond was obtained in a more stable bond state.
Here, the uneven distribution layer in which a component contained in the ceramic substrate and / or a part of the component contained in the bonding layer is unevenly distributed means that when a part of the component included in the ceramic substrate is unevenly distributed in the bonding layer, This refers to the case where a part of the components contained in the layer is unevenly distributed on the ceramic substrate and the case where the two cases are formed continuously or in contact with each other.
Further, the thickness of the uneven distribution layer is preferably 1 μm or more and 5 μm or less. If the thickness is less than 1 μm, a completely bonded 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 above the bonding layer is adversely affected. This is because the initial device performance cannot be obtained over time.
[0006]
Further, in the present invention, SiO ₂ forms a glass component to increase the bonding force, and the addition amount is very small, so that the ceramic substrate and the piezoelectric / electrostrictive film are not adversely affected. On the other hand, since the substrate material is mainly composed of zirconia, components of Y ₂ O ₃ , alkaline earth metal oxide, or rare earth metal oxide, which are easily dissolved in zirconia, can increase the binding force. Note that, when the substrate material is alumina, the alkaline earth metal oxide reacts with alumina to form a spinel compound, thereby increasing the bonding strength.
_{Incidentally, SiO 2, Y 2 O 3} , each addition amount of the alkaline earth metal oxide or rare earth metal oxide is preferably 0.3 wt% from 0.05 wt% in terms of oxide. If it is less than 0.05 wt%, there is no effect of improving the bonding force, and if it is more than 0.3 wt%, the substrate material and the piezoelectric electrostrictive film material are deteriorated, and the device characteristics change and the device strength decreases. It is because it makes it.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of a piezoelectric / electrostrictive film type element of the present invention in (a) a plane, (b) a longitudinal section taken 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 and an auxiliary electrode 8, a piezoelectric / electrostrictive film 5, and an upper electrode 6 on a ceramic substrate 1 composed of a thin diaphragm portion 3 and a thick portion 2. However, it is formed in an integral structure that 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 coupled in a completely coupled state by the coupling layer 7 made of an insulator, and the ceramic substrate 1 and the coupling layer 7 are coupled to each other. Is formed with a thickness of 1 to 5 μm in an unevenly distributed layer 7A in which a component included in the ceramic substrate 1 and / or a part of a component included in the bonding layer 7 is unevenly distributed.
[0008]
The material of the ceramic substrate 1 is preferably a material having heat resistance, chemical stability, and insulation. This is because, as will be described later, when the lower electrode 4, the piezoelectric / electrostrictive film 5 and the upper electrode 6 are integrated, heat treatment may be performed, and the piezoelectric / electrostrictive film type element as the sensor element has liquid characteristics. This is because the liquid may be conductive or corrosive when sensing.
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. Among these, stabilized zirconium oxide can be preferably used because the mechanical strength can be kept high and the toughness is excellent 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, and 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, or perfect circle, but in the application of a sensor element that needs to simplify the excited resonance mode, it may be a rectangle or true. A circle is selected as needed.
[0010]
The lower electrode 4 is formed from one end of the ceramic substrate 1 to be equal to the size on which the piezoelectric / electrostrictive film 5 is to be formed on the thin diaphragm portion 3, but is smaller or larger. However, 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 on 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 made of different materials or the same material, and a conductive material having good bonding property to both the ceramic substrate 1 and the piezoelectric / electrostrictive film 5 is used. Specifically, an electrode material mainly composed of platinum, palladium, rhodium, silver, or an alloy thereof is preferably used. In particular, when forming a piezoelectric / electrostrictive film, a heat treatment for sintering is performed. In this case, platinum and an alloy containing this as a main component are preferably used.
[0012]
Various known film forming techniques are used to form the lower electrode 4 and the auxiliary electrode 8. Specifically, thin film formation methods such as ion beam, sputtering, vacuum deposition, CVD, ion plating, plating, and thick film formation methods such as screen printing, spraying, and dipping are appropriately selected. A method and a screen printing method are preferably selected.
[0013]
Prior to the formation of the piezoelectric / electrostrictive film 5, a coupling layer 7 made of an insulator for forming a completely coupled 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 —xKNbO ₃ (x is a mole fraction) A material obtained by adding at least one selected from SiO ₂ , Y ₂ O ₃ , alkaline earth metal oxides, or rare earth metal oxides to 0.08 ≦ x ≦ 0.5) is preferable. In the case of these systems, it is preferable that Na or K is less than the stoichiometric composition so that Na and K are liberated and the insulating properties of the film are not impaired. For example, it is preferable that the molar ratio is 1.01 ≦ Bi / Na ≦ 1.08 and 0.92 ≦ (Bi + Na) /Ti≦0.98. Moreover, by being in this range, the generation of a heterogeneous phase of the piezoelectric film can be suppressed, and the particle diameter can be optimized for the expression of the element characteristics.
The bonding layer 7 is made of bismuth oxide sodium hydrogen tartrate, titanium oxide, potassium niobium hydrogen tartrate, and further weighed the oxides and carbonates of the additive components to a predetermined composition of the bonding layer, and in ethanol. , 2φ zirconia boulders were used and mixed for 16 hours in a ball mill. The obtained slurry was dried, calcined in the atmosphere at 900 ° C. for 2 hours, and further pulverized in ethanol using 2φ zirconia boulders. The pulverization time is selected so that the specific surface area of the pulverized powder is 5 to 10 m ² / g. Here, when it is smaller than 5 m ² / g, the activity of the powder is low, and therefore the reaction with zirconia does not proceed and an uneven distribution layer is not formed. When it is larger than 10 m ² / g, the activity is too high and the powders are aggregated, so that the uneven distribution layer cannot be formed uniformly.
The obtained powder uses polyvinyl butyral or ethyl cellulose as a binder component, terpineol or butyl carbitol as a solvent, and is kneaded with a tri-roll mill to form 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 -xKNbO ₃ (x is mol (1-x) (Bi _0.5 Na _0.5 ) TiO ₃ —xKNbO ₃ (x is a molar fraction of 0.08 ≦ 0.06) or a material mainly composed of this. The bonding layer 7 made of a material having x ≦ 0.5) as a main component has high adhesion between the piezoelectric / electrostrictive film 5 and the ceramic substrate 1, and the piezoelectric / electrostrictive film 5 and ceramics during the heat treatment. Since the bad influence to the board | substrate 1 can be suppressed, it uses more suitably. That is, the same component as the piezoelectric / electrostrictive film 5 is obtained by setting the bonding layer 7 to (1-x) (Bi _0.5 Na _0.5 ) TiO ₃ —xKNbO ₃ (x is 0.08 ≦ x ≦ 0.5 in terms of molar fraction). Therefore, the adhesiveness with the piezoelectric / electrostrictive film 5 is enhanced. In addition, there are few problems due to the diffusion of different elements that are likely to occur when glass is used, and since KNbO ₃ is contained in a large amount, it has high reactivity with the ceramic substrate and enables strong bonding. In addition, (1-x) (Bi _0.5 Na _0.5 ) TiO ₃ —xKNbO ₃ (x is 0.08 ≦ x ≦ 0.5 in terms of mole fraction) shows almost no piezoelectric properties, and therefore the lower electrode 4 and the auxiliary electrode 8 are not used during use. Therefore, stable element characteristics can be obtained because no vibration, displacement, or stress is generated with respect to the generated electric field.
[0015]
A normal thick film method is used to form these bonding layers 7, and in particular, a stamping method, a screen printing method, or an inkjet method when the size of a portion to be formed is about several tens to several hundreds of μm. Preferably used. Further, when the bonding layer 7 needs to be heat-treated, it may be heat-treated before the next piezoelectric / electrostrictive film 5 is formed, or may be simultaneously heat-treated after the piezoelectric / electrostrictive film 5 is formed.
[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 cover the lower electrode 4. The material of the piezoelectric / electrostrictive film may be any material that exhibits a piezoelectric / electrostrictive effect, such as lead zirconate, lead titanate, lead zirconate titanate (PZT), etc. Lead-based ceramic piezoelectric / electrostrictive materials, barium titanate and titavari-based ceramic ferroelectrics based on it, polymer piezoelectric materials represented by polyvinylidene fluoride (PVDF), or (Bi _0.5 Na _0.5 ) Bi ceramic ceramics represented by TiO ₃ and Bi layered ceramics can be mentioned. Of course, it is needless to say that a mixture, a solid solution, or a material obtained by adding an additive to these, which has improved piezoelectric / electrostrictive characteristics, can be used. The PZT-based piezoelectric body is suitably used as a sensor material having high piezoelectric characteristics and capable of high sensitivity detection. In particular, the material comprising at least one selected from lead titanate, lead zirconate, lead magnesium niobate and lead nickel niobate is a material constituting the ceramic substrate. Since the reactivity is low, segregation of components during the heat treatment hardly occurs, the treatment for maintaining the composition can be performed satisfactorily, and the intended composition and crystal structure are easily obtained, so that the composition is more preferably used.
[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 these is higher, the characteristic variation of the element is reduced, and high reliability is obtained. Therefore, for the piezoelectric / electrostrictive material, (Bi _0.5 Na _0.5 ) TiO ₃ or a material containing this as a main component is preferably used. Among these, in particular, (1-x) (Bi _0.5 Na _0.5 ) TiO ₃ —xKNbO ₃ (x is a molar fraction, 0 ≦ x ≦ 0.06) or a material having this as a main component has relatively high piezoelectric characteristics. Since it has, it is used more suitably.
[0018]
Such a piezoelectric / electrostrictive material is formed as the piezoelectric / electrostrictive film 5 by various known film forming methods in the same manner as the lower electrode 4 and the auxiliary electrode 8. Among these, screen printing is preferably used from the viewpoint of low cost.
[0019]
The piezoelectric / electrostrictive film 5 thus formed is heat-treated as necessary, and 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 bondability between the piezoelectric / electrostrictive film 5, the lower electrode 4, the auxiliary electrode 8, and the coupling layer 7 in order to suppress variations in element characteristics and increase 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 molar fraction, 0 ≦ x ≦ 0.06) Alternatively, heat treatment is preferably performed using a material mainly composed of this at a temperature of 900 ° C. to 1400 ° C., preferably 1000 ° C. to 1300 ° C. The same applies when using PZT-based materials. At this time, it is preferable to perform 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.
Then, after this heat treatment, an unevenly distributed layer 7A in which a component contained in the ceramic substrate 1 and / or a part of the component contained in the bonded layer 7 is unevenly distributed between the ceramic substrate 1 and the bonded layer 7 is shown in FIG. ) To a thickness of 1 to 5 μm.
[0020]
Further, the upper electrode 6 is continuously formed on the piezoelectric / electrostrictive film 5 thus formed so as to extend 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 the material of the upper electrode 6, a conductive material having high bondability with the piezoelectric / electrostrictive film 5 is used, and the upper electrode 6 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. It is the same as that of the lower electrode 4 that such a heat treatment is not always necessary.
[0021]
When the lower electrode 4, the bonding layer 7, the piezoelectric / electrostrictive film 5, and the upper electrode 6 are bonded by heat treatment, they may be heat-treated each time they are formed, You may heat-process. Needless to say, the heat treatment temperature is appropriately selected in order to suppress the deterioration due to good bondability and diffusion of constituent elements during the heat treatment. Moreover, although the lower electrode 4 etc. are laminated | stacked on the baked ceramic substrate 1, it is also possible to laminate | stack and bake the lower electrode 4, the bonding layer 7, etc. on the ceramic substrate 1 before baking. As a result, a case where a part of the components contained in the ceramic substrate is unevenly distributed in the bonding layer and a case where a part of the components contained in the bonding layer are unevenly distributed in the ceramic substrate are continuously or contacted. Thus, an uneven distribution 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 where 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 with 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 the main component and the bonding layer additive is SiO ₂ , the failure rate of the device after 300 hours is reduced when the addition amount is adjusted and the thickness of the uneven distribution layer is 1 μm or more and 5 μm or less. I can.
In addition, when the substrate material is mainly composed of zirconia, the bonding layer additive 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 also 0. When the thickness of the uneven distribution layer is 2 μm at 1 wt%, the failure rate of the element after 300 hours is sufficiently reduced.
Furthermore, even in the case of a tie layer additive in which SiO ₂ and Y ₂ O ₃ are mixed in increments of 0.1 wt%, the failure rate of the device after 300 hours is sufficiently reduced.
_{Further, SiO 2, Y 2 O 3} , is in the amount of the alkaline earth metal oxide or rare earth metal oxide is preferably 0.3 wt% from 0.05 wt% in terms of oxide. If it is less than 0.05 wt%, there is no effect of improving the bonding force, and if it is more than 0.3 wt%, the substrate material or the piezoelectric electrostrictive curtain material is deteriorated, and the device characteristics change or the device strength is reduced. .
[0025]
【The invention's effect】
In the piezoelectric / electrostrictive film type 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 becomes a more stable complete bond. Therefore, the durability as an element is increased, there is no variation in vibration or change with time, and an element for discriminating fluid characteristics and liquid / gas by detecting an electrical constant in vibration, or a measuring element for sound pressure, minute weight, acceleration, etc. In addition, suitable elements can be continuously obtained as actuator elements.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an embodiment of a piezoelectric / electrostrictive membrane 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 .... Binding layer 7A ... Unevenly distributed layer, 8 ... auxiliary electrode, 9 ... through hole, 10 ... cavity.

Claims (1)

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

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