JP2001284677A - Piezoelectric/electrostrictive element and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric/electrostrictive element and manufacturing method for it where no substrate degrades even if baking is performed while the substrate contacts the piezoelectric/electrostrictive element printed on it. SOLUTION: A baking process for a piezoelectric/electrostrictive element is provided where a film of a lower-part electrode film 6a, a piezoelectric/ electrostrictive film 5, and an upper-part electrode film 6b are formed on a substrate 1 whose main component is zirconia. Here, the piezoelectric/ electrostrictive film 5 is formed to be wider than the lower-part electrode film 6a so that the substrate contacts the piezoelectric/electrostrictive film 5, which is forcedly cooled when its temperature drops with at least temperature-drop rate, of 0.5 deg.C/minute or more from the range of 300 deg.C to 150 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wide range of fields such as frequency domain functional parts such as various transducers, various actuators and filters, various display devices such as displays, sounding bodies such as speakers, and microphones and ultrasonic sensors. Piezo that can be used in
The present invention relates to an electrostrictive element and a method for manufacturing the same.

[0002]

2. Description of the Related Art Piezoelectric / electrostrictive elements can be used in various fields as described above. The disclosed examples include a ceramic substrate acting as a diaphragm and a ceramic substrate provided on the substrate. In addition to a film-type piezoelectric / electrostrictive operating portion comprising a first electrode film, a piezoelectric / electrostrictive film, and a second electrode film (Japanese Patent Laid-Open No. 3-128681), a ceramic substrate has a cavity. Japanese Patent Application Laid-Open No. H05-205686 discloses a structure in which a bottom portion of a cavity has a thin-walled portion and a piezoelectric / electrostrictive operating portion is integrated on the thin outer surface.
No. 49270).

As a ceramic substrate constituting such a piezoelectric / electrostrictive element, a substrate using zirconium oxide partially stabilized with yttrium oxide is generally known (JP-A-5-29675, JP-A-5-29675). 97437, JP-A-5-270912). In the piezoelectric / electrostrictive element, a substrate is formed of a sintered body made of a mixture of zirconium oxide and yttrium oxide, for example, and a piezoelectric / electrostrictive film is formed. Is formed of a material containing, for example, lead zirconate titanate as a main component, a lower electrode film at a predetermined position on the substrate,
The piezoelectric / electrostrictive film and the upper electrode film are formed by printing and firing in this order. As a material for forming the piezoelectric / electrostrictive film, in addition to the above-mentioned material mainly containing lead zirconate titanate, a material mainly containing lead magnesium niobate and a material mainly containing lead nickel niobate Etc. Further, as the ceramic substrate, a zirconium oxide substrate partially stabilized by additives such as calcium oxide, magnesium oxide, and cerium oxide other than yttrium oxide is also used.

[0004]

As described above, the piezoelectric / electrostrictive element formed by printing, as shown in the cross-sectional view of FIG. 2, has a structure in which a piezoelectric / electrostrictive pattern is provided below the electrode film pattern. When the element is formed widely, it is easy to manufacture the element.
As shown in (b), the periphery protrudes from the lower electrode film to form a contact portion 7 with the substrate, and in the firing step, both compositions react with each other to affect the strength of the contact portion 7 of the substrate 1. This causes a decrease in strength, which hinders an improvement in yield.

In view of the above problems, the present invention provides a piezoelectric / electrostrictive device which does not affect the substrate even if the substrate is fired in a state where the substrate is in contact with the piezoelectric / electrostrictive film printed thereon. An object of the present invention is to provide a method for manufacturing an element, and to provide a piezoelectric / electrostrictive element in which the reliability of a portion of the substrate that functions as a diaphragm that is not covered by the lower electrode film, where stress is most likely to be applied, is improved. I do.

[0006]

The inventor of the present invention has found that the factors that hinder the improvement of the yield include lead, niobium, and titanium contained in the piezoelectric / electrostrictive material entering the substrate during the firing step, and the outside of the substrate (mainly, the piezoelectric / electrolyte). When the additive material used for the partial stabilization flows out into the strained film), for example, the additive material becomes Y2O
In the case of No. 3, the composition of the substrate contact portion is Y2 from the initial composition.
O3 is reduced and the composition of Y2O3 is 2.5 mol% or less, which is caused by T / M transformation from tetragonal to monoclinic in a cooling process after firing, and Y2O3 composition Is less than 2.5 mol%, the relationship between the monoclinic phase ratio and the decrease in substrate strength can be ascertained, and this phase transformation can be eliminated by manipulating the firing temperature characteristics, and the Y 2 O 3 composition is 2.5 mol%. The present invention has found a range of the monoclinic phase ratio in which cracks and the like do not occur in the following cases.
In the method of manufacturing an electrostrictive element, a lower electrode film, a piezoelectric / electrostrictive film, and an upper electrode film are sequentially formed on a substrate containing zirconia as a main component, and the piezoelectric / electrostrictive film is formed wider than the lower electrode film. Then, in the firing step of the piezoelectric / electrostrictive element in contact with the substrate, when the temperature is lowered, forced cooling is performed so that at least 3
The cooling rate from 00 ° C to 150 ° C is 0.5 ° C / min or more. This control of the temperature decreasing rate is similarly effective even when the additive material is calcium oxide, magnesium oxide, cerium oxide or the like. By making the temperature drop rate steep in this way, even if firing is performed in a state where the substrate and the piezoelectric / electrostrictive film are in contact with each other, no T / M transformation occurs in the substrate, and a reduction in the strength of the substrate is prevented. Can be.

According to a second aspect of the present invention, in the first aspect, the composition of the substrate is 2.5 to 3.5 mol% Y2O.
It is configured as 3-ZrO2. Here, the composition of the substrate means the initial composition before firing, but when the added amount of Y2O3 is less than 2.5 mol%, the temperature drop rate is made steep because the added amount is small in consideration of the reduced amount of Y203. Can not prevent the strength of the substrate from decreasing,
If it exceeds 1%, the desired amount of substrate cannot be obtained because the amount of addition is too large even when the amount of Y2O3 reduction is considered.

[0008] Further, the invention of claim 3 is based on claim 1 or 2
In the invention, the average cooling rate from 300 ° C. to 150 ° C. is 0.7 ° C./min or more. The effect is more preferably at 275 ° C. to 175 ° C.

According to a fourth aspect of the present invention, there is provided a piezoelectric / electrostrictive element in which a lower electrode film, a piezoelectric / electrostrictive film, and an upper electrode film are sequentially formed on a substrate mainly composed of zirconia. Contains Y2O3, and the portion of the substrate not covered by the lower electrode film has a Y2O3 composition ratio of 1.5 to 2.5 mol%.
And the monoclinic phase ratio of the site on the substrate is 2.0%.
In the composition range, the monoclinic phase ratio is 2.0% or less, so that the substrate is covered with the lower electrode film that is most likely to be stressed among the substrates that function as a diaphragm. The characteristics of such a portion can be made excellent in hardness and the like, and a piezoelectric / electrostrictive element used without reducing the strength of the substrate can be obtained. Preferably, the effect is remarkable at a monoclinic phase ratio of 1.5% or less.

[0010]

Embodiments of the present invention will be described below. FIG. 2A schematically shows the configuration of the piezoelectric / electrostrictive element according to the present invention. This is the same as the structure of the conventional piezoelectric / electrostrictive element.

The substrate 1 is formed by stacking and firing a plurality of green sheets composed of 3 mol% Y2O3-ZrO2. The piezoelectric / electrostrictive film 5 is made of PbO, ZrO2, TiO2
As shown in FIG. 2, a lower electrode film 6a and an upper electrode film 6b are respectively provided on a lower portion facing the substrate 1 and an upper portion facing the substrate 1 as shown in FIG. The electrostrictive film 5 has a lower electrode film 6a formed on the substrate.
It is formed by printing and firing at 1200 ° C. to 1300 ° C.

The firing process will be described with reference to the firing temperature profile shown in FIG. 1. As shown in FIG. 1, the profile until the maximum temperature is reached is not different from the conventional setting. Is greatly changed, and the temperature is lowered by forced cooling. In this forced cooling, it is particularly preferable that the average temperature drop time from 300 ° C. to 150 ° C. is 0.5 ° C./min or more.
When the average temperature drop rate to 0 ° C. is 0.7 ° C./min or more, the monoclinic phase ratio can be reduced as shown in FIG. The temperature range in which the forced cooling is performed is particularly 275 ° C to 1 ° C.
A temperature of 75 ° C. has a more remarkable effect.

Next, specific manufacturing processes and characteristics of the piezoelectric / electrostrictive element will be described. First, the substrate 1 is made of ZrO2-3 mol% Y2O.
3 green sheets 1400
Firing at ~ 1500C to obtain a zirconia substrate. Next, a piezoelectric / electrostrictive element is formed. Pt is used as the lower electrode film 6a.
The paste is formed on a zirconia substrate by screen printing and fired. And PbO, ZrO2, TiO2,
A paste containing a piezoelectric powder containing Nb205 as a main component is screen-printed on the lower electrode film 6a,
By firing at 0 ° C., the lower electrode film 6 of the piezoelectric / electrostrictive element 5 is formed.
a and the piezoelectric / electrostrictive film 5 are formed. Then, in the cooling process of the firing step, air was sent into the furnace from a temperature around 500 ° C. in the furnace, so that the passage time from 300 ° C. to 150 ° C. was 192 minutes (0.78 ° C./min).

By forcibly cooling the cooling step in this manner, 3 mol of Y 2 O 3 of the zirconia
However, the monoclinic phase ratio (ratio to the tetragonal system) was 1.3%, and no crack was generated. Incidentally, when the forced cooling was not performed in the production process of Example 1, the passage time from 300 ° C. to 150 ° C. was 556 minutes (0.27 ° C./min), and the monoclinic phase ratio was 3.4. %, And cracks were observed.

FIG. 3 shows the results of the change in the monoclinic phase ratio when the cooling rate is changed as described above. The shorter the passage time from 300 ° C. to 150 ° C., the smaller the monoclinic phase ratio. It can be seen that cracks do not occur at 2.0% or less, more preferably at 1.5% or less. Incidentally, the monoclinic phase ratio was measured by X-ray diffraction of the substrate including the reaction part of the contact portion 7 of the zirconia substrate 1 by the monoclinic (111) plane peak height /
It was determined from the tetragonal (101) plane peak height (%). As described above, the Y2O3 of the zirconia substrate 1 at the contact portion 7 is reduced by about 1.0 mol% from the initial composition, but the monoclinic phase ratio is 2.0% or less, more preferably 1.
When the content is set to 5% or less, no influence on the substrate such as a crack occurs.

By forced cooling as described above, even if the printed piezoelectric / electrostrictive film is baked in a state in which the edge is in contact with the substrate, the substrate contact portion undergoes T / M transformation to cause cracks and the like. And good characteristics can be maintained. The forced cooling may be performed by air cooling in which air is directly fed into the furnace. However, if water cooling is performed by providing a water pipe inside the heat insulator of the furnace, temperature control can be easily performed. In addition, although the temperature drop characteristics in the case of natural cooling differ depending on the size and structure of the firing furnace, the substrate characteristics can be improved by forced cooling in any furnace.

[0017]

As described in detail above, according to the first to third aspects, even if the edge of the piezoelectric / electrostrictive film is in contact with the substrate before firing, the piezoelectric element does not adversely affect the substrate. And both can be sintered favorably. According to the fourth aspect, 1.5 to 1.5 are applied to the portion of the substrate where stress is most likely to be applied.
By setting the monoclinic phase ratio to 2.0% or less with 2.5 mol% Y 2 O 3, a more reliable piezoelectric / electrostrictive element can be obtained.

[Brief description of the drawings]

FIG. 1 is a temperature profile of a firing step, which is a main part of a method for manufacturing a piezoelectric / electrostrictive element, showing an example of an embodiment of the present invention.

FIGS. 2A and 2B are explanatory cross-sectional views of a piezoelectric / electrostrictive element according to the present invention, wherein FIG. 2A shows a state after firing and FIG. 2B shows a state after printing of a piezoelectric / electrostrictive film.

FIGS. 3A and 3B show a monoclinic phase ratio and a state of occurrence of cracks when a cooling rate is changed in a firing step. FIG. 3A is a measurement result data table, and FIG. 3B is a graphed data thereof.

[Explanation of symbols]

1. substrate, 2. flow path, 5. piezoelectric / electrostrictive film, 6a
· Lower electrode film, 6b · · · Upper electrode film.

Claims (4)

[Claims] A lower electrode film, a piezoelectric / electrostrictive film, and an upper electrode film are sequentially formed on a substrate containing zirconia as a main component, wherein the piezoelectric / electrostrictive film is formed wider than the lower electrode film; In the firing step of the piezoelectric / electrostrictive element in contact with
A method for manufacturing a piezoelectric / electrostrictive element, wherein forced cooling is performed when a temperature is lowered, and a rate of temperature decrease from at least 300 ° C. to 150 ° C. is 0.5 ° C./min or more. 2. The composition of the substrate is 2.5-3.5 mol.
2. The method for producing a piezoelectric / electrostrictive element according to claim 1, wherein the composition is% Y2O3-ZrO2. 3. The piezoelectric / cylinder according to claim 1, wherein an average temperature drop rate from 300 ° C. to 150 ° C. is 0.7 ° C./min or more.
A method for manufacturing an electrostrictive element. 4. A lower electrode film, a piezoelectric / electrostrictive film, and an upper electrode film are sequentially formed on a substrate containing zirconia as a main component, the substrate containing Y2O3, and covering the lower electrode film of the substrate. The Y2O3 composition ratio of the uncoated part is 1.5 to 2.5.
mol%, and the monoclinic phase ratio of the portion of the substrate is 2.0% or less.