JPH07131086A - Piezoelectric film type element and its treatment method and drive method - Google Patents

Abstract

PURPOSE:To achieve piezoelectric characteristics at a level which can be fully utilized even if no polarization treatment is performed by allowing a piezoelectric body film constituting a piezoelectric actuation part to have polarization directed from the upper electrode to the lower electrode. CONSTITUTION:By utilizing a piezoelectric layer (film) 6 in the process for forming a piezoelectric actuation part 10 and stress according to a thermal expansion difference with electrode films 4 and 8 and ceramic substrate 2 (2a), a shrinkage rate, etc., an electrical dipole is orientated from the side of the upper electrode 8 toward the side of the lower electrode 4 and a self-generation polarization is formed. Then, the upper electrode 8 of the piezoelectric film type element is subjected to polarization treatment as a positive pole and further a ratio Ya/Yb, where Ya is the amount of displacement obtained when a drive voltage is applied with the upper electrode 8 as the positive pole and the lower electrode 4 as the negative pole and Yb is the amount of displacement obtained when the lower electrode 4 is subjected to polarization treatment as a positive electrode and further a drive voltage is applied with the lower electrode 4 as the positive electrode, is set to 1.05 or less, thus achieving improved characteristics for the title piezoelectric type element.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a piezoelectric film type element, and in particular, a unimorph mainly used for servo valves, motors, pumps, transformers, microphones, sounding bodies (speakers, etc.), various vibrators and oscillators, and sensors. The present invention relates to a piezoelectric film type element such as a mold or a bimorph type, which generates a bending displacement or force or detects a bending displacement or force. The element referred to herein means not only an element that converts electrical energy into mechanical energy, that is, mechanical displacement or stress or vibration, but also an element that performs the opposite conversion.

[0002]

BACKGROUND ART In recent years, in fields such as optics and precision processing,
A displacement element that adjusts the optical path length and position on the order of submicrons and a detection element that detects a minute displacement as an electrical change have been desired, and in response to this, a piezoelectric material such as a ferroelectric substance is used. The development of a piezoelectric element used for an actuator or a sensor, which is an element utilizing the phenomenon of displacement based on the inverse piezoelectric effect that occurs when an electric field is applied to a material, or the opposite phenomenon is under development.

Among them, as a structure using such a piezoelectric element, a conventionally known unimorph type or bimorph type has been favorably adopted. Also,
For such a piezoelectric element, cost reduction, miniaturization,
Furthermore, low voltage driving and low voltage response are required,
Development is in progress.

By the way, in order to meet the demands for further miniaturization and low voltage driving of such a piezoelectric element, in order to realize it, the substrate and the piezoelectric layer constituting the piezoelectric element are made thin so that they can be easily bent. It is considered effective to do so and to improve the characteristics of the piezoelectric material itself that provides the piezoelectric layer. However, as the substrate of the piezoelectric element or the piezoelectric layer is made thinner, its strength decreases, causing a problem in mechanical reliability, or the variation in the thickness of the piezoelectric layer causes the operating characteristics to vary widely. There was such a problem. Further, as the thickness of the piezoelectric layer is reduced, dielectric breakdown may occur when a predetermined electric field is applied,
There was also a problem with electrical reliability. Further, various studies have been added for a long time to improve the characteristics of the piezoelectric material, and it seems that improvement measures have been exhausted, and at present, a significant improvement cannot be expected.

On the other hand, the piezoelectric material is generally superior in electromechanical conversion efficiency to the electrostrictive material and has excellent characteristics as a displacement element and a detection element. However, in order to obtain the excellent functional characteristics of this piezoelectric element, it is essential to apply a voltage after firing to align the electric dipole alignment state of the piezoelectric layer (piezoelectric body) (polarization treatment step). In some cases, the polarization treatment for obtaining this sufficient characteristic may require the use of a condition of applying a high voltage (electric field) for several hours at a high temperature of 80 ° C. to 200 ° C. . Moreover, in such a polarization treatment, a continuity test is performed in advance because of the low reliability of electrical contact at high temperature.
It is also necessary to check whether or not the subsequent polarization treatment can be surely performed, or whether or not the polarization is surely performed after the treatment. For this reason, in general, there is a problem that the manufacturing cost of the polarization treatment process becomes high, and further, there is a problem in stability and reliability of piezoelectric characteristics due to variations in the polarization treatment.

Further, in the case of a piezoelectric film type element in which a film-shaped piezoelectric actuating portion composed of a lower electrode, a piezoelectric film and an upper electrode is integrally formed on a thin ceramic substrate, Since it is extremely difficult to attach the film to the substrate after polarization is applied to the film-shaped piezoelectric actuator, it is usually necessary to keep the piezoelectric actuator (piezoelectric film) fixed to the substrate. A method of performing polarization treatment will be adopted. In such a method, the piezoelectric actuator, specifically, the piezoelectric film is changed from the substrate when the piezoelectric film is changed from the non-polarized state to the polarized state. There is an inherent problem that the piezoelectric film type element is subjected to stress and adversely affects its piezoelectric characteristics to hinder the performance enhancement of the piezoelectric film type element.

[0007]

The present invention has been made in view of such circumstances, and its object is to provide a piezoelectric characteristic of a level that can be sufficiently used without polarization treatment. To provide a piezoelectric element having the piezoelectric film type element which has sufficient piezoelectric characteristics by a simpler method than before and has stable characteristics even when polarization treatment is performed. It is to provide the piezoelectric film type element with high performance and high quality by polarization treatment. Another object of the present invention is to provide an effective polarization treatment method for such a piezoelectric film type element and further a driving method.

[0008]

In order to solve the above problems, the present invention comprises a thin ceramic substrate and a lower electrode, a piezoelectric film, and an upper electrode that are sequentially provided in layers on the ceramic substrate. Amount of displacement (Ya) obtained when a piezoelectric film type element having a film-like piezoelectric actuating part is formed, polarization is performed with the upper electrode as a positive electrode, and a drive voltage is applied with the upper electrode as a positive electrode. Under the same conditions as in the case of the upper electrode, the ratio (Ya) of the displacement amount (Yb) obtained when the lower electrode is polarized as a positive electrode and a driving voltage is further applied with the lower electrode as a positive electrode. / Y
The gist is a piezoelectric film type element characterized in that b) is 1.05 or more.

In the piezoelectric film type element according to the present invention, when the polarization treatment is performed to further improve the performance, the upper electrode of the piezoelectric film type element is used as the positive electrode, and the lower electrode is therefore the negative electrode. As a result, a predetermined polarization process is performed.

Further, when the piezoelectric film type element which is or is not subjected to such a polarization treatment is driven for use as an actuator, the upper electrode of the piezoelectric film type element is used as a positive electrode and the lower electrode is As the negative electrode, a predetermined driving voltage is applied, so that a large displacement can be advantageously obtained.

[0011]

As described above, according to the present invention, in a piezoelectric film type element provided with a thin ceramic substrate and a film-shaped piezoelectric actuator integrally provided on the substrate, the piezoelectric actuator is
When a piezoelectric film is integrally formed on a substrate by a film forming method such as a thick film forming method, when the piezoelectric actuator is completely formed,
The piezoelectric film forming the piezoelectric actuating portion is polarized in the direction from the upper electrode to the lower electrode (in a polarized state), in other words, the electric dipole is oriented. Therefore, even if the polarization treatment is not performed, the piezoelectric film type element exhibiting a characteristic of a level that can be sufficiently used depending on the application can be obtained, and it can be advantageously used particularly in a device in which the polarization treatment is difficult. It was decided. That is, this piezoelectric film type element is directly applied to its intended use without being subjected to polarization treatment, and when used, the upper electrode and the lower electrode, which form the piezoelectric actuator together with the piezoelectric film, become the positive electrode and the lower electrode become the negative electrode. Thus, the external electric field is applied and the driving is effectively performed.

Further, since the piezoelectric film type element according to the present invention is in a pre-polarized state, the upper electrode serves as the positive electrode and the lower electrode is arranged from the upper electrode side even when the polarization treatment by the external electric field is performed. By applying an electric field along the direction toward the side, the polarization treatment can be performed easily and effectively, and exhibits excellent performance as compared with a normal piezoelectric element that is not pre-polarized. In addition to stabilizing its characteristics, such polarization treatment can reduce stress and strain between the piezoelectric actuator (piezoelectric film) and the diaphragm (substrate) that occur when the electric dipoles are aligned. The adverse effect can be advantageously avoided or reduced, and excellent piezoelectric characteristics can be obtained.

Further, when the piezoelectric film type element according to the present invention is subjected to the polarization treatment, it is in the same direction as the orientation direction of the electric dipole in the piezoelectric actuating portion (piezoelectric film), that is, from the upper electrode side. If polarization processing is performed in the direction toward the lower electrode side, the piezoelectric characteristics (displacement characteristics) superior to those of the conventional piezoelectric element can be enjoyed. That is, the same effect as improving the material characteristics can be obtained without changing the piezoelectric material itself.

Furthermore, when the piezoelectric film type element according to the present invention is actually driven and used as an actuator, the upper electrode is made to be the positive electrode regardless of the presence or absence of the polarization treatment as in the case of the polarization treatment described above. At the same time, it is effective that the lower electrode is used as a negative electrode and an external electric field is applied so that the lower electrode can be driven, whereby more excellent characteristics can be exhibited.

The piezoelectric film type element according to the present invention having the above characteristics can obtain a large displacement at a relatively low operating voltage, is excellent in strength and has high reliability, has a fast response speed, and can be generated. The power is great, there is little variation between individuals,
Servo valves, motors, pumps, transformers, microphones, low cost devices that can be highly integrated.
It can be suitably used for a sounding body (speaker or the like), various vibrators and oscillators, and further acceleration sensors, pressure sensors, vibration sensors, angular velocity sensors and the like.

[0016]

Concrete Structure By the way, FIG. 1 shows an example of a basic structure of a piezoelectric film type device to which the present invention is applied.
There, the ceramic base body 2 has a thick outer wall portion and a thin wall portion 2a whose inner portion is a ceramic substrate.
It is said that. Then, on the outer surface of the thin wall portion 2a of the ceramic substrate 2, the lower electrode film 4, the film-shaped piezoelectric layer 6 and the upper electrode film 8 are sequentially laminated by a normal film forming method to form a film. The piezoelectric actuator 10 is integrally formed. The lower electrode film 4 and the upper electrode film 8
Are respectively extended from the ends of the piezoelectric layer 6,
The lead portions 4a and 8a are formed, and the lead portions 4a and 8a are formed.
A predetermined voltage is applied to each of the electrode films 4 and 8 through a and 8a.

In the piezoelectric film type element having such a structure, when the piezoelectric film type element functions as an actuator, the two electrode films 4 constituting the piezoelectric actuating portion 10,
When current is applied between 8 and in the same manner as in the conventional case, and an electric field is caused to act on the piezoelectric layer 6 by this, an electric field induced strain is caused due to such an electric field, and a lateral effect of this electric field induced strain is caused. , Ceramic substrate (thin wall 2a)
The bending displacement or force in the direction perpendicular to the plate surface of the plate is expressed.

By the way, in such a piezoelectric film type element, as a material for providing the ceramic base 2 having the thin thickness portion 2a which is the ceramic substrate on which the piezoelectric actuating portion 10 is formed, various known materials are used. It can be used as appropriate, but especially by the present inventors
As disclosed in the above publication, by adding a compound such as yttrium oxide, the crystal phase is mainly tetragonal, or at least 2 of cubic, tetragonal and monoclinic.
A material containing zirconia partially stabilized as a main component by using a mixed crystal composed of one or more crystal phases is preferably used. By using a ceramic substrate made of such a material, even if the thickness is thin, the mechanical strength is high, the toughness is high, and the chemical reaction with the piezoelectric material is small. The ceramic base 2
Is a lamination of a thin green sheet to be the thin wall portion 2a onto a green sheet provided with holes or windows using a machining method such as a die or ultrasonic processing, thermocompression bonding, and then firing and integration. From the viewpoint of high reliability, it is preferable to manufacture by Further, regarding the thickness of the thin wall portion 2a of the ceramic base 2 on which the piezoelectric actuator 10 is formed,
In order to obtain high-speed response and large displacement of the element, the thickness of the part is generally 50 μm or less, preferably 30 μm.
Hereafter, it will be more preferably 10 μm or less.

In order to form the piezoelectric actuating portion 10 by providing the predetermined electrode films 4 and 8 and the piezoelectric layer 6 on the ceramic substrate 2 (thin-walled portion 2a), various known film forming methods are used. The method is appropriately adopted, but in forming the piezoelectric layer 6, a thick film forming method by screen printing, spraying, coating, dipping, coating or the like is preferably adopted. If this thick film forming method is used, the average particle diameter is 0.0
This is because it is possible to form a film on a ceramic substrate using a paste or slurry containing piezoelectric ceramic particles of 1 μm or more and 7 μm or less, preferably 0.05 μm or more and 5 μm or less as a main component, and obtain good device characteristics. . Among the thick film forming methods, the screen printing method is particularly preferably used because fine patterning can be formed at low cost. In addition, as the thickness of the piezoelectric layer 6,
In order to obtain a large displacement at a low operating voltage, preferably 5
It is desirable that the thickness is 0 μm or less, and more preferably 3 μm or more and 40 μm or less.

The electrode material for the lower electrode film 4 and the upper electrode film 8 constituting the piezoelectric actuator 10 is as follows.
The conductor is not particularly limited as long as it can withstand a high temperature oxidizing atmosphere, and may be, for example, a simple metal or an alloy, or a mixture of an insulating ceramic and a simple metal or an alloy thereof. Also, even if it is a conductive ceramic, there is no problem. However, more preferably, a high melting point noble metal such as platinum, palladium, or rhodium, or an electrode material containing an alloy such as silver-palladium, silver-platinum, or platinum-palladium as a main component, or platinum and a ceramic substrate material or a piezoelectric material. The cermet material of and is preferably used. Among these, it is more preferable to use only platinum or a material containing a platinum-based alloy as a main component. The ratio of the substrate material added to the electrode material is preferably about 5 to 30% by volume, and the ratio of the piezoelectric material is preferably about 5 to 20% by volume.

Each of the electrode films 4 and 8 is formed by using the above-mentioned conductor material, or the above-mentioned thick film forming method or thin film forming method such as sputtering, ion beam, vacuum deposition, ion plating, CVD or plating. The film is formed according to the film forming method according to the above. Among them, regarding the formation of the lower electrode film 4, screen printing,
Thick film forming techniques such as spraying, dipping, and coating are preferably adopted, generally 1 to 30 μm, preferably 3 to 2
Even if the upper electrode film 8 is formed to have a thickness of 0 μm, the above-described thin film forming method is also suitably used in addition to the same thick film forming method. Generally, when the thickness is 20 μm or less, preferably 5 μm or less. Will be formed.

The piezoelectric material for forming the film-shaped piezoelectric layer 6 in the piezoelectric actuator 10 is preferably a material containing lead zirconate titanate (PZT system) as a main component, lead magnesium niobate (PMN system). , Lead nickel niobate (PNN type) as main component, lead manganese niobate as main component, lead antimony stannate as main component, lead zinc niobate as main component A material containing a component, a material containing lead titanate as a main component, a composite material of these, and the like are used. Furthermore, in these piezoelectric materials,
Additives such as lanthanum, barium, niobium, zinc, cerium, cadmium, chromium, cobalt, antimony, iron, yttrium, tantalum, tungsten, nickel, manganese, lithium, strontium and bismuth, and other compounds thereof. A material added as the above, for example, a material obtained by appropriately adding a predetermined additive to the above-mentioned material so as to be a PLZT system is also preferably used.

Among these piezoelectric materials, a material containing a lead magnesium niobate, lead zirconate, and lead titanate as a main component, or lead nickel niobate, lead magnesium niobate, and lead zirconate. A material whose main component is lead titanate is advantageously used, and is recommended as a material for forming the piezoelectric layer 6 by the thick film forming method such as the screen printing described above. In the case of a multi-component piezoelectric material, the piezoelectric characteristics change depending on the composition of the components, but in the three-component material of lead magnesium niobate-lead zirconate-lead titanate which is preferably adopted in the present invention, The composition in the vicinity of the phase boundary of pseudo-cubic crystal-tetragonal crystal-rhombohedral crystal is preferable, and particularly lead magnesium niobate: 15-5
A composition of 0 mol%, lead zirconate: 10-45 mol%, lead titanate: 30-45 mol% is advantageously adopted because of its high piezoelectric constant and electromechanical coupling coefficient.

Further, as described above, the respective films (4, 6 and 6) formed on the thin wall portion 2a which is the ceramic substrate.
In 8), each time each film is formed, it may be heat-treated (baked) so as to have an integrated structure with the substrate. Alternatively, after forming all the films, heat-treated (baked) at the same time. The membrane may simultaneously be integrally bonded to the substrate. Depending on the method of forming the electrode films (4, 8), the heat treatment (baking) for such integration may not be necessary. Further, as the heat treatment (baking) temperature for integrating the film thus formed and the substrate, a temperature of about 900 ° C to 1400 ° C is generally adopted, and preferably a temperature in the range of 1000 ° C to 1400 ° C. Is advantageously selected. Further, when heat-treating (baking) the film-like piezoelectric layer 6, heat treatment (baking) is performed while controlling the atmosphere together with such a piezoelectric material evaporation source so that the composition of the piezoelectric layer does not become unstable at high temperatures. ) Is preferable,
It is also recommended to adopt a method of placing an appropriate cover member on the piezoelectric layer 6 so that the surface thereof is not directly exposed to the firing atmosphere and firing is performed. In that case, a material similar to that of the substrate is used as the cover member.

The present invention provides a piezoelectric film type element having such a structure in which the piezoelectric layer (film) 6 and the electrode films 4 and 8 and the ceramic substrate 2 (2a) in the step of forming the piezoelectric actuating portion 10 are formed. It was found that the electric dipole can be oriented in the direction from the upper electrode (8) side to the lower electrode (4) side by utilizing the stress due to the difference in thermal expansion and contraction rate with It was completed based on that.

Specifically, in the manufacture of a piezoelectric film type element, specifically, (a) control of the linear expansion coefficient of the substrate material and the piezoelectric material, (b) the ratio of the thickness of the substrate and the piezoelectric layer (piezoelectric film). By appropriately performing control and (c) control of the firing profile, the electric dipole is advantageously moved in the direction from the upper electrode (8) to the lower electrode (4) at the completion of formation of the piezoelectric actuator 10. It can be oriented (polarized state), and in particular, the upper electrode of the piezoelectric film type element is polarized as a positive electrode (the lower electrode becomes a negative electrode), and the upper electrode is further used as a positive electrode and a lower electrode. The amount of displacement (Ya) obtained when a drive voltage is applied as a negative electrode, and under the same polarization treatment and drive voltage application conditions as in the case of the upper electrode, the lower electrode is polarized as a positive electrode, and the lower electrode is further polarized. As the positive electrode By setting the ratio (Ya / Yb) to the displacement amount (Yb) obtained when a drive voltage is applied to be 1.05 or more, preferably 1.1 or more, more preferably 1.2 or more, It was possible to impart excellent characteristics to such a piezoelectric film type element.

In order to obtain a piezoelectric film type device having a particularly large electric field induced strain and a high Ya / Yb value, the coefficient of linear expansion of the substrate material that provides the ceramic substrate 2 is preferably 60 to 120 × 10 ^−7. / ° C, more preferably 80-
110 × 10 ⁻⁷ / ° C. is desirable, and the linear expansion coefficient of the piezoelectric material that provides the piezoelectric layer (piezoelectric film) 6 of the piezoelectric actuator 10 is preferably 1 to 80 × 10 ⁻⁷ / ° C. It is preferably 10 to 30 × 10 ⁻⁷ / ° C.,
And the difference in their linear expansion coefficient (substrate material-piezoelectric material)
Is preferably 30 to 120 × 10 ⁻⁷ / ° C., more preferably 30 to 100 × 10 ⁻⁷ / ° C.

Further, a piezoelectric layer (piezoelectric film) laminated on the thin wall portion 2a of the ceramic substrate 2 with the lower electrode film 4 interposed therebetween.
When firing 6 to be integrated with such a thin portion 2a, the temperature rising rate as a firing temperature profile is preferably 400 ° C./hour or less, more preferably 2
50 ° C / hour or less, more preferably 150 ° C / hour or less, and after firing, 800 ° C
Average temperature falling rate in the above temperature range (calcination temperature to 800
It is desirable that the temperature lowering rate between the temperatures is 700 ° C./hour or less, more preferably 350 ° C./hour or less, and further preferably 200 ° C./hour or less, whereby a large electric field is induced in the piezoelectric film type element. Distortion and high Ya
It is possible to give the / Yb value. 8
Since the rate of temperature decrease in the temperature range of 00 ° C. or lower does not significantly affect the characteristics of the piezoelectric film type element, generally, in such a range, it is possible to cool by cooling, etc. as in the conventional case. Becomes

Furthermore, the ratio of the thickness of the ceramic substrate 2 (thin-walled portion 2a) to the piezoelectric layer (piezoelectric film) 6 constituting the piezoelectric actuator 10 in the piezoelectric film type element also depends on the electric field induced strain and Ya.
/ Yb value, large electric field induced strain and high Ya / Y
In order to obtain the b value, the piezoelectric actuator 1 of the ceramic substrate 2
When the thickness of the portion where 0 is provided (thin wall thickness portion 2a) is Hs and the thickness of the piezoelectric layer (piezoelectric film) 6 is Hp, the thickness ratio (Hp / Hs) is preferably 1 to 10, It is desirable to set the value within the range of preferably 2 to 8, and more preferably 3 to 6.

In summary, by appropriately combining these manufacturing conditions, a piezoelectric film type device having a large electric field induced strain and a high Ya / Yb value can be advantageously manufactured, and thereby a piezoelectric film type device can be manufactured. Since the film-type element is in a pre-polarized state, it can be used as it is because it exhibits characteristics that can be sufficiently used for some applications without polarization treatment. The same direction as the orientation of the child (upper electrode film 8
From the lower electrode film 4 to the lower electrode film 4), the orientation of the dipole can be more effectively performed, and further excellent characteristics can be obtained, and the characteristics are stable. The piezoelectric actuating portion 10 (piezoelectric layer 6) and the vibration plate (thin-walled thick portion 2) which exhibit the characteristics and are further generated when the dipoles are aligned.
From the fact that the adverse effects of stress and strain between a) can be reduced, and also due to this, excellent characteristics can be obtained.

Further, such Ya / Yb according to the present invention is
In order to more effectively exert the characteristics of the piezoelectric film type element having a value by polarization treatment, in the present invention, the temperature is generally room temperature to 200 ° C., preferably 50 ° C. to 120 ° C. An electric field of 1 kV / mm to 5 kV / mm, preferably 1.5 kV / mm to 3.5 kV / mm is generally 1 minute to 5 hours, preferably 10 minutes to 90 minutes, and the upper electrode is applied to the piezoelectric film type element. It will be applied as a positive electrode.

By the way, in the polarization treatment of the piezoelectric film type element, it is generally known that the hysteresis curve showing the relationship between the external electric field applied to the element and the amount of polarization in the element can be measured by the Sawyer / Tawa circuit shown in FIG. In such a circuit, a piezoelectric film type element as a measurement sample is measured with its upper electrode (8) connected to the point A side and its lower electrode (4) connected to the point B side. That will be the case.

3 (a) and 3 (b) of FIGS. 3 (a) and 3 (b) show an example in which the hysteresis curves of the piezoelectric film type device according to the present invention and the conventional piezoelectric film type device are measured by such a Sawyer / Tawa circuit. However, the difference is obvious when the hysteresis curves are compared. That is, these hysteresis curves have an external electric field E on the horizontal axis and a polarization P (or electric flux density D) on the vertical axis,
As shown, in the conventional piezoelectric film type element,
As shown in FIG. 3 (a), a point-symmetrical shape centered on the origin is shown, whereas in the case of the piezoelectric film type element according to the present invention, as is clear from FIG. The hysteresis curve deviates from the shape.

In the polarization treatment, the direction of the electric field from the upper electrode (8) to the lower electrode (4) is positive, Pa: spontaneous polarization in the positive direction, Pb: spontaneous polarization in the negative direction, Ea: positive direction. Where Eb is the coercive electric field in the negative direction, in the hysteresis curve of the piezoelectric film type element according to the present invention, when spontaneous polarization (Pa) in the positive direction is compared with spontaneous polarization (Pb) in the negative direction, Pa / Since Pb> 1, the positive coercive electric field (Ea) and the negative coercive electric field (Ea) are obtained.
Comparing with b), Ea / Eb> 1.
Note that this deviation indicates the degree of polarization orientation, and it can be said that in order to increase the Ya / Yb value, it is preferable that the deviation of the hysteresis curve is large.

The structure of the piezoelectric film type element according to the present invention manufactured here, the shape of the film-shaped piezoelectric actuating portion 10,
The structure and the like are not limited to those illustrated,
It is determined appropriately according to the application. A specific example thereof is disclosed in Japanese Patent Application Laid-Open No. 5-28, filed by the applicant of the present application.
9257, JP-A-6-40035, and further JP-A-5-
Various types are disclosed in No. 97437 and the like, and any of them can be appropriately adopted.

For example, a large number of piezoelectric film type elements may be integrally arranged and used depending on the application of the piezoelectric film type element, but the present invention applies to each of these piezoelectric film type elements. On the other hand, it can be applied independently.

FIG. 4 shows an example of a piezoelectric film type element having a bimorph structure. There, electrode layers 14 are formed in advance on both sides of the piezoelectric layer 12 on the back side of the thin wall portion 2a in the piezoelectric film type device shown in FIG. 1, that is, on the surface on which the piezoelectric actuation portion 10 is not provided. Plate-shaped piezoelectric body 1
6 is attached via the adhesive layer 18 to form a bimorph structure. In such a structure, the Ya / Yb value according to the present invention is set to 1.05 or more in the one piezoelectric film type element portion composed of the thin wall portion 2a and the piezoelectric operation portion 10 on the surface thereof. The Rukoto.

Further, in the piezoelectric film type element shown in FIG. 5, the two piezoelectric actuating portions 10 are integrally formed on the front and back surfaces of the thin wall portion 2a of the ceramic substrate 2 so as not to overlap each other. It is said to have been constructed. Then, the present invention is independently applied to each piezoelectric film type element portion constituted by each piezoelectric actuating portion 10 and the portion of the thin wall portion 2a where it is located. Therefore, it goes without saying that the present invention can be applied to only one piezoelectric film type element portion. Although FIG. 5 shows an example in which the piezoelectric actuating portions 10 and 10 on both front and back sides do not overlap, the piezoelectric actuating portions 10 and 1 do not overlap.
Even if 0's partially overlap, it does not matter.

[0039]

EXAMPLES Hereinafter, representative examples of the present invention will be shown to clarify the present invention in more detail. However, the present invention is not limited by the description of such examples. Needless to say, it is not something to receive. In addition to the following embodiments, the present invention is not limited to the above specific description, and various changes and modifications are made based on the knowledge of those skilled in the art without departing from the spirit of the present invention. It is to be understood that improvements, etc. can be added.

Example 1 First, in the piezoelectric film type elements of Examples 1, 2, and 3 of the present invention, and Comparative Example 1, a material containing zirconium oxide partially stabilized with yttrium oxide as a main component was used. A sintered body having a cavity shape having a thin wall portion (2a) as shown in (3) was prepared according to a conventional method and used as a ceramic substrate (2). The thickness of the thin wall portion (2a) was 10 μm, and the size of the thin wall portion (2a) was 0.8 mm × 3 mm.

Then, a lower electrode film (4) is formed on the thin wall portion (2a) of the ceramic substrate (2) by screen printing using a paste prepared by adding an organic binder and an organic solvent to platinum powder. Formed, then 1300
It was fired at a temperature of ° C. The thickness of this lower electrode film (4) is
The firing operation resulted in 5 μm.

Then, on the lower electrode film (4),
Further, a piezoelectric layer (6) was formed with a thickness of 30 μm.
The piezoelectric layer (6) was formed by using a piezoelectric material containing a lead magnesium niobate, lead zirconate, and lead titanate as a main component, and having a thickness of 30 after firing.
A method of screen-printing so as to have a thickness of μm and performing firing (heat treatment) at a predetermined temperature was adopted. The temperature profile during firing of this piezoelectric material (piezoelectric layer 6), that is, the temperature rising rate, firing temperature, and temperature reduction rate (between firing temperature and 800 ° C.) are as shown in Table 1 below. Also, 800
The temperature decrease below ℃ was performed by natural cooling.

[0043]

[Table 1]

Further, in addition to the lower electrode film (4) and the piezoelectric layer (6) laminated on the thin wall portion (2a) of the ceramic substrate (2), a Cr film (8) is used as an upper electrode film (8). The lower layer) and the Cu film (upper layer) were sequentially formed by sputtering. In addition, Cr film (lower layer)
The Cu film (upper layer) and the Cu film both had a thickness of 0.2 μm (thus, the thickness of the upper electrode film 8 was 0.4 μm).

Further, in Comparative Example 2, a piezoelectric element was manufactured by a method of attaching a piezoelectric plate instead of the film forming method as described above. The same material as described above was used as the substrate material, a lower electrode film (4) having a thickness of 5 μm was formed with a conductive adhesive, and the substrate was fired in advance with the firing temperature profile shown in Table 1 to 30 μm. A thick piezoelectric plate was attached to manufacture. The upper electrode film (8) was formed in the same manner as the piezoelectric film type element described above.

The amounts of displacement (Ya, Yb) according to the present invention were measured for the various devices thus obtained, and the results are shown in Table 2 below. The polarization treatment condition is temperature: 10
0 ° C., electric field: 3 kV / mm, treatment time: 1 hour. The displacement amount was measured by applying a drive voltage having a pulse waveform of 40V. Here, the direction of polarization is defined as the forward direction with the upper electrode film (8) as the positive electrode and the reverse direction with the lower electrode film (4) as the positive electrode. The voltage was applied according to such a defined direction.

In the test A, first, the displacement amount Yo when the forward drive voltage is applied to each element in the state where the polarization process is not applied is measured, and then the displacement amount is applied by the polarization process in the forward direction. (Ya) is measured, and then the polarization amount is applied in the reverse direction to measure the displacement amount (Yb). Finally, the polarization amount is applied again in the forward direction to measure the displacement amount (Ya ′). The reproducibility of the measurement was confirmed by the fact that ′ was approximately equal. Similarly, in the test B, the reverse polarization process is first performed to measure the displacement amount (Yb), then the forward polarization process is performed to measure the displacement amount Ya, and finally the reverse direction is again performed. Polarization processing is performed and the displacement (Yb ') is measured.
The reproducibility of the measurement was confirmed by the fact that b and Yb 'were substantially equal.
The procedure of Test A and Test B is as follows.

Test A: Displacement amount Yo measurement (forward drive voltage) ↓ Forward polarization process ↓ Displacement amount Ya measurement (forward drive voltage) ↓ Reverse polarization process ↓ Displacement amount Yb measurement (reverse drive voltage) ↓ Again Forward polarization process ↓ Displacement amount Ya 'measurement (forward drive voltage) Test B: Reverse direction polarization process ↓ Displacement amount Yb measurement (reverse drive voltage) ↓ Forward polarization process ↓ Displacement Ya measurement (forward drive voltage) ↓ Reverse polarization process again ↓ Displacement Yb 'measurement (reverse drive voltage)

[0049]

[Table 2]

As is clear from the results shown in Table 2,
In the piezoelectric film type element according to the present invention, high Ya / Yb
It has a value, and shows a sufficiently large displacement (Yo value) by applying a predetermined drive voltage even if polarization processing is not performed, and further shows a higher displacement amount (Ya value) by polarization processing. -ing On the other hand, in the piezoelectric film type element according to Comparative Example 1, the Ya / Yb value was low, and accordingly the displacement amount (Ya, Yb) was inferior. In addition, the piezoelectric plate sticking type element of Comparative Example 2 has a piezoelectric material firing condition similar to that of Example 1 of the present invention, but is different from the element of Example 1 of the present invention. The displacement amount (Ya) was significantly inferior.

[Brief description of drawings]

FIG. 1 is a perspective partial explanatory view showing an example of a piezoelectric film type element to which the present invention is applied.

FIG. 2 is a circuit diagram showing a Sawyer / Tawa circuit for observing a hysteresis curve of a piezoelectric element.

3 is a diagram showing an example of a hysteresis curve obtained by using the Sawyer-tower circuit shown in FIG.
Shows a conventional piezoelectric film type element, and (b) shows a piezoelectric film type element according to the present invention.

FIG. 4 is a perspective partial explanatory view showing another example of the piezoelectric film type element to which the present invention is applied.

FIG. 5 is a perspective partial explanatory view showing still another example of a piezoelectric film type element to which the present invention is applied.

[Explanation of symbols]

 2 Ceramic Substrate 4 Lower Electrode Film 6 Piezoelectric Layer 8 Upper Electrode Film 10 Piezoelectric Actuating Part 12 Piezoelectric Layer 14 Electrode Layer 16 Plate Piezoelectric Body 18 Adhesive Layer

Front page continuation (72) Inventor Masato Komazawa 2-56 Sudamachi, Mizuho-ku, Aichi Prefecture Nagoya City

Claims (3)

[Claims] 1. A piezoelectric film type device comprising: a thin ceramic substrate; and a film-shaped piezoelectric actuating portion composed of a lower electrode, a piezoelectric film and an upper electrode, which are sequentially provided in layers on the ceramic substrate. , A displacement amount (Ya) obtained when the upper electrode is polarized as a positive electrode and a driving voltage is further applied with the upper electrode as a positive electrode, and the lower electrode is set under the same conditions as those of the upper electrode. The ratio (Ya / Yb) to the displacement amount (Yb) obtained when polarization is applied as the positive electrode and a drive voltage is applied with the lower electrode as the positive electrode is
A piezoelectric film type element having a thickness of 1.05 or more. 2. The piezoelectric film type element according to claim 1, wherein
A method of treating a piezoelectric film type element, characterized in that polarization treatment is performed using the upper electrode as a positive electrode. 3. When driving the piezoelectric film type element according to claim 1 or the piezoelectric film type element obtained by polarization treatment according to claim 2, a predetermined electrode is used as an upper electrode of the piezoelectric film type element. A method of driving a piezoelectric film type element, characterized in that a driving voltage is applied.