JP2001102648A - Laminated piezoelectric transducer element and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated piezoelectric transducer element, in which laminated bodies are firmly coupled with each other and delamination hardly occurs among the laminates and which can obtain large displacement and a high drive speed. SOLUTION: A laminated piezoelectric transducer element is manufactured, in such a way that a laminate composed of alternately laminated PZT layers 23 and electrode layers 24 is formed by alternately packing a prescribed quantity of piezoelectric ceramic (hereinafter called 'PZT') powder 2 containing PZT (PbZrO3.PbTiO3) and a prescribed quantity of an electrode material, such as the platinum material, platinum foil, etc., in a cylindrical space constituted of a die 3 and punches 4 and 5. Then the die 3 and punches 4 and 5 are loaded in a discharge plasma sintering device, and the layers 23 and 24 are sintered to each other by heating the laminate in the temperature range of 850-1,100 deg.C, by supplying a pulse-like current of a prescribed voltage and a prescribed frequency to the laminate, while the powder 2 is pressurized with a pressure of >5 MPa by pressurizing the punches 4 and 5 by means of a pressurizing mechanism.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer piezoelectric transducer and a method for manufacturing the same.

[0002]

2. Description of the Related Art Piezoelectric transducers have a high conversion efficiency for converting supplied electric energy into driving force and are easy to control the generated driving force, so that they can be used in cameras, measuring instruments, and other precision machines. It has been used as a drive source of an actuator for driving and positioning a drive member.

[0003] The most basic configuration of a piezoelectric conversion element is as follows.
A multi-layer piezoelectric transducer composed of a plurality of unit piezoelectric elements laminated, and composed of a plurality of unit piezoelectric elements laminated, requires that the displacement in the thickness direction generated in the unit piezoelectric element be as large as possible. To take it out.

[0004] There are roughly two methods of manufacturing a laminated piezoelectric transducer. The first manufacturing method is called a single-plate laminated type, in which a thin plate-shaped piezoelectric base material made of a piezoelectric ceramic material is baked and polished to form a predetermined number of laminated piezoelectric element single plates. I do. Next, the piezoelectric element single plates are sequentially laminated while sandwiching a conductive paste also serving as an electrode material and an adhesive, and then cut into a predetermined size to produce a predetermined number of laminated piezoelectric transducers.

The second manufacturing method is called a green sheet lamination type, in which a piezoelectric ceramic material and additives such as a binder resin and a plasticizer are added to an appropriate solvent and uniformly stirred to form a slurry of the piezoelectric base material. create. Next, the slurry of the piezoelectric base material is applied to a carrier sheet with a thickness of several tens of μm using a uniform thin film coating device such as a coater, dried, and then separated from the carrier sheet, thereby forming a piezoelectric sheet called a green sheet. A material sheet is obtained.

Next, a conductive paste serving as an electrode material is applied to the surface of the green sheet by a method such as screen printing, cut into a predetermined size, and sequentially laminated by a predetermined number of sheets. This is for producing a predetermined number of laminated piezoelectric transducers.

In the method of laminating the baked piezoelectric element single plates, cracks may occur during the polishing and laminating operations, so that the thickness of the piezoelectric element single plate is limited.
Thicknesses of about μm or more are often used. On the other hand, since the green sheet contains a binder resin, it is flexible, and the thickness of the green sheet veneer is 10 to 5 mm.
The thickness can be reduced to about 0 μm.

For this reason, in the green sheet laminated type piezoelectric transducer, the thickness of each layer can be reduced, so that the electric field strength can be increased. Therefore, when the same displacement is generated by low-voltage driving, the dimension in the height direction (the laminating direction of the piezoelectric veneer) becomes shorter than that of the veneer-type piezoelectric transducer,
The size of the device can be reduced.

[0009]

In order to increase the displacement or the driving speed of either a single-plate laminated piezoelectric transducer or a green-sheet laminated piezoelectric transducer,
When the driving pulse voltage applied to the element and the driving frequency thereof are increased, the multi-layer piezoelectric conversion element self-destructs. Most of the damage during the driving is peeling between the laminates (hereinafter, referred to as delamination).

[0010] Therefore, the limits of the voltage applied to the element and the driving frequency are set to a voltage below the voltage at which dielectric breakdown of the element occurs and a voltage and frequency within a range in which delamination does not occur.
That is, when the voltage is applied to the element, the concentration of the strain due to the sudden expansion of the element is suppressed, and thus the drive pulse waveform is prevented from rising sharply and the drive frequency is also rapidly changed. There are various restrictions, such as lowering the resonance frequency.

In order to prevent delamination of the laminated piezoelectric conversion element, it is necessary to increase the bonding strength between the element and the electrode material. In addition, in the case of a single-plate laminated type piezoelectric transducer, in order to equalize the inclination of the laminate and the electric field strength between the layers, the piezoelectric element single plate is polished by lapping or the like to obtain a highly accurate flat and thick element. Need to finish. Further, in the green sheet laminated type piezoelectric transducer, warpage occurs during firing, resulting in a defective product, and the yield is not good. As described above, there are problems that need to be solved in the manufacturing process in the case of a laminated piezoelectric conversion element. However, the present invention aims to solve the above problems.

[0012]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems. According to the first aspect of the present invention, a piezoelectric material and an electrode material are alternately laminated and compressed to increase the adhesion between the respective layers. In this state, the temperature was increased to 850 while applying a pressure exceeding 5 MPa.
A multilayer piezoelectric conversion element characterized by being sintered by an electric conduction sintering method at a temperature of not less than 1100 ° C and not more than 1100 ° C.

According to a second aspect of the present invention, in the first aspect, the piezoelectric material is a powder containing lead zirconate titanate or a green sheet using the powder, and the electrode material is platinum, palladium, nickel or the like. Powder, foil or conductive paste containing at least one selected from the group consisting of: 850 ° C. while applying a pressure exceeding 5 MPa
A multi-layer piezoelectric conversion element characterized by being sintered by a current sintering method at a temperature of 900 ° C. or more and 1000 ° C. or less while applying a pressure of less than 1100 ° C., preferably more than 10 MPa. Further, a spark plasma sintering method can be used as the electric current sintering method.

According to a fourth aspect of the present invention, a piezoelectric material and an electrode material are alternately laminated, and the temperature is increased to 850 ° C. while applying a pressure exceeding 5 MPa in a state where the adhesion between the layers is increased by compression.
A method for producing a multilayer piezoelectric transducer, comprising sintering at a temperature of 900 ° C. or more and 1000 ° C. or less while applying a pressure of at least 1100 ° C., preferably over 10 MPa, and then cooling to room temperature. It is.

According to a fifth aspect of the present invention, in the fourth aspect, the piezoelectric material is a powder containing lead zirconate titanate or a green sheet using the powder, and the electrode material is platinum, palladium or nickel. Powder, foil or conductive paste containing at least one selected from the group consisting of: 850 ° C. while applying a pressure exceeding 5 MPa
A method for producing a multilayer piezoelectric transducer, comprising sintering at a temperature of 900 ° C. or more and 1000 ° C. or less while applying a pressure of at least 1100 ° C., preferably over 10 MPa, and then cooling to room temperature. It is. Also,
A spark plasma sintering method can be used for the electric current sintering method.

[0016]

Embodiments of the present invention will be described below.

[Spark Plasma Sintering Method] First, a spark plasma sintering method, which is one of the electric current sintering methods, will be described. Discharge plasma sintering is a method of sintering by generating a discharge plasma by applying a pulsed current while applying pressure to the powder loaded in the mold, and sintering without causing particle growth. This is a sintering method capable of producing a sintered body having a higher density than the raw material powder.

That is, a pulse-shaped current is applied while the raw material powder is being pressed, and the peak current and the pulse width are controlled to compress and sinter while controlling the material temperature. Utilization of discharge phenomena generated in the gaps between powder particles, activation of purification of particle surfaces by discharge plasma, discharge impact pressure, etc., electrolytic diffusion effect of electric field, thermal diffusion effect by Joule heat, plastic deformation force by pressurization, etc. Promotes sintering.

As the discharge plasma sintering apparatus, one capable of heating, cooling and pressurizing the raw material powder and applying a voltage sufficient to generate a discharge is required.

FIG. 1 is a view schematically showing the structure of a discharge plasma sintering apparatus. A discharge plasma sintering apparatus 1 includes a die 3 which is a molding die for loading and molding a powder 2 and a die 3 above and below the die 3. It is composed of a pair of compression and energization punches 4, 5 arranged.

The punches 4 and 5 are provided with upper and lower extensions 4a,
5a is provided, and the punches 4 and 5 are configured to press and compress the powder 2 through the extension portions 4a and 5a by hydraulic pressure or other means supplied from the pressing mechanism 12. Further, cooling water passages 9a are provided inside the extension portions 4a and 5a.
9b is formed, and the punches 4 and 5 are configured to be cooled by cooling water supplied from the cooling mechanism 15.

The die 3, the punches 4, 5 and their extensions 4a, 5a are housed inside a vacuum chamber 8. The vacuum chamber 8 is connected to an atmosphere control mechanism 14, and keeps the die 3 and the punches 4, 5 in a vacuum of a predetermined degree of vacuum, or in an atmosphere of an inert gas such as argon gas, and furthermore, in the atmosphere. It is configured so that it can be kept in the atmosphere.

The die 3 and the punches 4 and 5 are made of a conductive material such as graphite, and electrodes 6 and 7 are attached to the ends of the punches 4 and 5 respectively. It is connected to a power supply 13 and configured to supply a pulse current to the powder 2 loaded inside the die 3.

A control device 11 is provided for controlling the pressurizing mechanism 12, the sintering power supply 13, the atmosphere control mechanism 14, and the cooling mechanism 15, and the control device 11 has a die (not shown). Sensors for detecting temperature, pressure, and other information are connected to each other so that predetermined control is performed.

In the above-described configuration, the piezoelectric ceramic powder 2 is loaded into a space formed by the die 3 and the punches 4 and 5 having a desired shape, a predetermined atmospheric gas is injected into the vacuum chamber 8, and a pressurizing mechanism is provided. By supplying a pulse current from the power source 13 for sintering while pressing the powders 2 by pressing the punches 4 and 5 by the 12, a sintered body having a desired shape can be produced.

[Sintering and Forming Step of Piezoelectric Conversion Element] The sintering and forming step of the piezoelectric conversion element using the above-mentioned discharge plasma sintering apparatus will be described below.

FIG. 2 is a sectional view showing a state in which the piezoelectric ceramic powder is loaded in the die 3 and the punches 4 and 5. First, the die 3 and the punches 4 and 5 are made of graphite. A carbon paper 21 is wound around the inner peripheral surface of the die 3 to prevent seizure. The lower punch 5 is inserted into the inner surface of the die 3, and the carbon paper 22 cut out to the same diameter as the punch 5 is also placed on the punch 5.

Next, a cylinder constituted by the die 3 and the punch 5
In the space of the shape, the piezoelectric ceramic (piezoelectric material)
Lead zirconate, abbreviated PZT (PbZrO_Three・ PbT
iO _Three) As the main component (hereinafter, referred to as piezoelectric ceramic powder)
PZT) and an electrode material such as white
Gold powder is charged, and these materials are charged alternately by a predetermined amount.
And a PZT layer 23 and an electrode layer 24 alternately stacked.
It is loaded so that several layers of the laminate are formed. At this time,
The layers are stacked such that the PZT layer is located on the uppermost layer and the lowermost layer.

After the predetermined number of layers is completed, the uppermost PZT
The carbon paper 25 is placed on the layer, and the punch 4 is inserted into the die 3 from above, and the lid is closed.

The die 3 and the punches 4 and 5 in which the PZT layers 23 and the electrode layers 24 are alternately laminated are mounted on the discharge plasma sintering apparatus 1 described above, and a predetermined atmospheric gas is supplied to the vacuum chamber 8. At the same time, the punches 4 and 5 are driven by the pressurizing mechanism 12 to drive and press the powder 2 to supply a pulse current of a predetermined voltage and frequency from the sintering power supply 13 to heat and sinter. . This process is called a discharge plasma sintering process (hereinafter, may be abbreviated as SPS process).

Next, a heat oxidation treatment is performed on the sintered body obtained in the SPS processing step. That is, since the above-mentioned die 3 and punches 4 and 5 are made of graphite, graphite adheres to the surface of the sintered body which has been fired and turns black, and a part of the PZT composition is reduced by the reduction action of graphite. Occurrence of oxygen vacancies lowers the electrical resistance, and the sintered body may become conductive.

Therefore, the sintered body is heated to 600 ° C. to 850 ° C. in an oxygen or air atmosphere using an electric furnace to thermally decompose and remove the adhered graphite and to reduce the composition of reduced PZT. Eliminates oxygen deficiency (ie oxidation)
Then, a stacked piezoelectric transducer in which the PZT layers 23 and the electrode layers 24 are alternately stacked is completed.

In the above-mentioned thermal oxidation treatment, it is desirable to carry out thermal oxidation treatment at a high temperature sufficient to thermally decompose graphite, and it is desirable to carry out heating at 600 ° C. or higher.
When heated at a temperature of at least C., the lead component, which is one of the components constituting PZT, which is a piezoelectric material, starts to evaporate as PbO, and the composition changes to significantly lower the performance.
A temperature range from ℃ to 850 ℃ is suitable.

[Embodiment 1] Hereinafter, an embodiment of a specific manufacturing process of a laminated piezoelectric transducer (hereinafter, referred to as a PZT element) will be described. First, in Example 1, PZ was used as the piezoelectric material.
The T powder uses platinum powder as an electrode material. In this embodiment, the inner diameter of the die 3 is about 20.2.
mm and the outer diameter of the die 3 is about 40 mm. Also, PZT
The thickness of the powder layer is about 100 μm, and the thickness of the platinum powder layer is about 5
μm, the number of layers of the PZT layer 23 is 10, and the number of layers of the electrode layer 24 is 9.

In the SPS process, the temperature rise rate is 100 ° C.
/ Min, the supply pulse current was set so as to satisfy this condition, heated to 1000 ° C., maintained in this state for 5 minutes, and then cooled naturally to room temperature. The pressure condition at this time is 40 MPa.

The fired sintered body is in a state where the carbon papers 22 and 25 are baked and fixed to the upper and lower end surfaces. Therefore, the carbon papers 22 and 25 on the upper and lower end surfaces are polished and removed. The resultant was heated and oxidized by heating, and the attached graphite was thermally decomposed to eliminate oxygen deficiency in the composition of the PZT element.

The change in electric resistance between the electrodes due to the heat oxidation treatment will be described. As described above, immediately after performing the discharge plasma sintering process, the electrical resistance between the electrodes is about several kΩ to several tens of kΩ due to the graphite adhered to the surface, and between the electrodes of the multilayer piezoelectric conversion element. The electric resistance is too low to polarize by applying a voltage.

That is, the required electric field at the time of polarization is usually 1500 to 3000 V / mm, even if it depends on the composition of PZT which is a material constituting the piezoelectric transducer. In the case of Example 1 described above, the required polarization electric field is 1500 V / mm at 60 ° C., and after the sintering process, the thickness of one PZT element layer is about 80%.
Since it has contracted to μm, the applied voltage for the polarization process is 1500 × 0.08 = 120V. Immediately after the discharge plasma sintering process is performed, the electric resistance between the electrodes is low. Therefore, when a voltage of 120 V is applied between the electrodes, a discharge occurs between the electrodes and the element is destroyed. It is indispensable to make the electrical resistance of the high resistance state.

FIG. 3 shows the electrical resistance between the electrodes immediately after performing the discharge plasma sintering process and the electrical resistance between the electrodes after performing the heating process. As is clear from FIG. 3, immediately after the SPS processing, the resistance value is 10 ³ to 10 ^3
It can be seen that the value of ⁷ Ω becomes 10 ⁹ Ω or more by the heat oxidation treatment.

FIG. 4 is a graph showing the results of measuring the relationship between the maximum temperature and pressure applied during SPS processing and the amount of displacement obtained with the completed conversion element of the PZT element manufactured by SPS processing. The axis represents the maximum temperature (° C.) of the spark plasma sintering treatment, and the axis of ordinate represents the displacement (nm).

In this measurement, the sample PZT element uses a 10-layer PZT element consisting of one inactive PZT element at the top and bottom and eight active PZT elements in the middle, and the die 3 850 ° C, 900 ° C, 9
100 ℃ / mi up to 50 ℃, 1000 ℃, 1050 ℃
The temperature was raised at a rate of n, held for 5 minutes, and then cooled to room temperature. Further, as the pressing force, 5 MPa, 10 MPa, 20
Five conditions of MPa, 40 MPa, and 60 MPa were set. In FIG. 4, the line (a) has a pressure of 10 MPa, the line (b) has a pressure of 20 MPa, and the line (c) has a pressure of 40 MPa.
a and line (d) show the case of a pressure of 60 MPa.

The die temperature was measured by measuring the surface temperature of the graphite die 3 with a radiation thermometer. The sintering temperature of the PZT element inside the die differs depending on the pressurization condition, but it is 100 ° C to 250 ° C higher than the die surface temperature in the temperature measurement of the dummy sample incorporating the thermocouple. Has been confirmed. The actual sintering temperature of the PZT element was managed by checking the correlation between the internal temperature of the die and the surface temperature in advance.

As a sample PZT element material, HIZIRCO-AD manufactured by Hayashi Chemical Industry Co., Ltd. was used. The value of the piezoelectric constant d33 of the catalog value of this material is 570 × 10 ⁻¹² m
The theoretical displacement calculated from / V is 364 nm when a DC voltage of 80 V is applied.

The sample PZT element was set to SP under the above conditions.
FIG. 4 shows the result of applying a DC voltage of 80 V to the completed sample PZT device after performing the S process, the heat oxidation process, and the polarization process, and measuring the displacement amount. Note that a step meter Dektak manufactured by Japan Vacuum Engineering Co., Ltd. was used for measuring the displacement amount.

As is apparent from FIG. 4, when the pressing force is large, the displacement performance tends to be improved even at a lower sintering temperature, and when the die temperature is 900 ° C. and the pressing force is 20 MPa or more,
It can be seen that an actual displacement of 80% or more of the theoretical displacement can be obtained.

Further, it was confirmed that the displacement performance as a piezoelectric transducer was obtained under all conditions, although the measured displacement was large or small. At 1050 ° C., the displacement performance decreased under all pressurization conditions because at high temperatures, the lead component, one of the components constituting PZT, was evaporated as PbO, and this was due to the use of EDX. Pb in quantitative analysis of Pb
It has been confirmed that the amount of b has decreased.

Although not shown in FIG. 4, when the temperature exceeds 1100 ° C., the tendency of evaporation of PbO becomes remarkable, so that not only the composition of PZT changes but the displacement performance decreases, but also PbO
Discharge plasma sintering becomes difficult, for example, the graphite die is damaged by the gas vapor pressure of the gas. Note that FIG. 4 does not show data in the case where the pressure is 5 MPa, but this is because current could not be stably supplied at a pressure of 5 MPa, and the temperature could not be increased to a target temperature. is there. The reason why the upper limit of the pressing force is set to 60 MPa is due to the restriction of the strength of the graphite die.
When using dies made of stronger materials,
Further, the pressing force can be increased.

FIG. 5 is a cross-sectional view of the above-mentioned laminated piezoelectric transducer.
The maximum temperature and pressure conditions of the spark plasma sintering process,
The figure which shows the measurement result of the relationship of a bulk specific gravity is shown, the horizontal axis | shaft shows the highest attainment temperature (degreeC) of a discharge plasma sintering process, and a vertical axis | shaft shows a bulk specific gravity.

In FIG. 5, line (a) is a pressure of 10MPa.
a, line (b) is pressure 20MPa, line (c) is pressure 4
0MPa and the line (d) show the case of a pressure of 60MPa.

In this measurement, the sample P
Each layer of the ZT element was cut with a dicing saw to cut out a block containing no electrode layer, and the bulk specific gravity was measured by a buoyancy method. In comparison with FIG. 4, it can be seen that the conditions under which the specific gravity is high and the sintering can be performed densely coincide with the conditions under which the displacement performance is high. The catalog specific gravity of the sample PZT element material is 7.7.

FIG. 6 is a diagram showing the test results of the breaking strength between the stacks of the above-mentioned sample PZT elements. In the breaking strength test, the sample PZT element 20 was cut in a direction orthogonal to the lamination direction so that the cross section became a 1 mm square laminated PZT element, and the 1 mm square cross section was held by two upper and lower members shown in FIG. It was placed between the tools 31 and 32 and adhered, and a tensile test was performed using a universal testing machine (not shown) manufactured by Instron.

In FIG. 6, what is indicated by NB indicates that the element itself did not break, but ultimately peeled off at the bonding portion S between the holders 31, 32 and the PZT element 20. In this case, when the strength at the time of peeling was 3 kgf / mm ² or less and it was considered that the adhesion was poor, the test was repeated.

As is apparent from FIG. 6, the breaking strength between the layers of the PZT element prepared by the SPS process is sufficiently higher than the breaking strength between the layers of the commercially available PZT element manufactured by the conventional manufacturing method.

Example 2 In Example 2, a platinum foil was used as an electrode material. In the first embodiment described above, platinum powder or palladium powder was used as the electrode material.
It is necessary to stack the layers in a layer having a thickness of about the same, which increases the manufacturing cost of the piezoelectric transducer.

Therefore, in Example 2, platinum foil was used as an electrode material. It is also possible to use a metal foil having high heat resistance and corrosion resistance other than platinum. The other configuration and the manufacturing method are the same as those in the first embodiment, and thus the description is omitted. Example 1 also shows the displacement characteristics of the completed laminated piezoelectric transducer.
It is no different from that of.

FIG. 8 is a view showing the test results of the breaking strength between the layers of the sample PZT element of Example 2. The breaking strength test was performed by the same method as the breaking strength test of Example 1. As is clear from FIG. 8, the PZT element of Example 2 has a lower breaking strength than that of Example 1, but it is sufficiently higher than the breaking strength between the laminations of a commercially available one manufactured by the conventional manufacturing method. I understand.

Example 3 In Example 3, a PZT layer was formed by using a green sheet previously formed to a predetermined thickness instead of PZT powder. The green sheet is as already described in the description of the related art in the detailed description of the invention of the present specification.

In order to drive the stacked piezoelectric transducer at a low voltage and obtain high displacement characteristics, it is necessary to reduce the thickness of each PZT layer to increase the electric field strength and further increase the number of stacked layers. General.

When the PZT powder is used to form the PZT layer as in the first and second embodiments, the thickness of the PZT layer varies, or the electrodes between the layers penetrate the PZT layer and are interposed between the other layers. The possibility of occurrence of troubles such as a short circuit with the electrode is increased.

In particular, as the area of the element is increased by using a large-diameter die, reducing the thickness of the PZT layer is more likely to cause the above-described problems such as variations and short circuits.
Therefore, in the third embodiment, a green sheet formed to a predetermined thickness in advance is used to form the PZT layer.

In the third embodiment, platinum paste is screen-printed on one side of a green sheet having a thickness of 30 μm to form an electrode having a thickness of about 3 μm. Next, the green sheet on which the electrodes are formed is punched into a disk having a size suitable for the inner diameter of the die 3, and a predetermined number of the green sheets are stacked inside the die 3 with the electrode surface facing upward. A green sheet on which no electrode is formed is laminated on the uppermost part.

Thereafter, as in the first and second embodiments, the SP
By performing the S treatment, the heat oxidation treatment, and the polarization treatment, a laminated piezoelectric conversion element is completed. However, in the spark plasma sintering process, the temperature rise up to 500 ° C. is gradual, for example, 50 ° C./min.
And slowly raise the temperature. Also, during this gradual heating period, the pressure is set low, for example, 10 MPa, so that the gas generated by the thermal decomposition of the binder and the like inside the green sheet is sufficiently released. After the heating up to 500 ° C. was completed, the same heating and pressurizing conditions as in Examples 1 and 2 were used.

As for the displacement performance of the completed laminated piezoelectric transducer, the same displacement performance as that of the first embodiment can be obtained with the same number of laminated layers. Since a green sheet is used for the PZT layer, each layer can be easily formed into a thin layer having a uniform thickness, and the number of laminated layers can be increased. A piezoelectric transducer having a large displacement can be produced.

FIG. 9 is a view showing the test results of the breaking strength between the layers of the sample PZT element of Example 3. The breaking strength test was performed by the same method as the breaking strength test of Example 1. As is clear from FIG. 9, the sample of Example 3 has a lower breaking strength than that of Example 2, but is sufficiently higher than the breaking strength between the layers of a commercially available product obtained by the conventional manufacturing method. .

As described above, since the laminated piezoelectric transducer manufactured by the discharge plasma sintering method is sintered in a pressurized state in a molding die, distortion such as warping of the outer shape and swelling of the internal electrode are caused. Since the baking can be performed without causing the deformation, the baking requires little secondary processing such as polishing or lapping.

As described above, when graphite is used as a molding die, graphite adheres to the surface of the sintered element and turns black, and the reduction action of graphite reduces the composition of the PZT element. In some cases, electrical resistance is lowered due to partial oxygen deficiency. Therefore, it is necessary to perform heat treatment to remove graphite and oxidize the material having the oxygen deficiency.

However, when using a mold made of a material having no reducing action, such as ceramics such as alumina or zirconia, or a metal or a heat-resistant alloy having high high-temperature strength, the above-mentioned obstacles due to the adhesion of graphite do not occur. So
There is no need for heat treatment.

The characteristics of the spark plasma sintering method can be summarized as follows.
It is as follows. First, it takes about 12 hours when firing in a normal electric furnace, but it can be performed in 15 to 30 minutes when firing a multilayer piezoelectric conversion element by a discharge plasma sintering method.

Second, since the powdered piezoelectric material can be fired as it is, there is no need to adjust a material containing a binder or a plasticizer, and it becomes unnecessary to remove the binder before firing. In the firing step, the growth of particles is suppressed, and a high-density sintered body can be obtained.

Third, the bonding between different kinds of materials, which is difficult to bond by ordinary firing, is relatively easy, and it is possible to effectively and firmly bond a laminate made of a large number of piezoelectric materials with electrodes interposed therebetween. it can.

[0071]

As described above, according to the multilayer piezoelectric transducer of the present invention, a piezoelectric material and an electrode material are laminated in a desired number of layers, and compressed to increase the pressure between the layers to increase the adhesion. Plasma sintering method (S
PS), the possibility that the laminates are strongly bonded to each other and peeling between the laminates is extremely low.

As a result, it becomes possible to increase the drive pulse voltage applied to the element and the drive frequency thereof, as compared with the case of the conventional multilayer piezoelectric transducer, thereby increasing the displacement and the drive speed as compared with the conventional one. It is possible to increase.

Further, as in the case of the conventional single-plate laminated type piezoelectric transducer, in order to equalize the inclination of the laminate and the electric field strength between the layers, the piezoelectric element single plate is subjected to a polishing process such as lapping or the like. It is not necessary to finish the device with a plane and thickness with high precision, and it does not cause warpage during firing as in the case of a green sheet laminated type piezoelectric conversion element, resulting in a defective product. The firing of the piezoelectric conversion element, which was required for 15 hours or more, was changed to the discharge plasma sintering method (S
According to (PS), even if a cooling time is included, it is completed in about 30 minutes, and the productivity can be remarkably improved in terms of time, and a remarkable effect is exhibited.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a configuration of a spark plasma sintering apparatus.

FIG. 2 is a sectional view showing a state in which a piezoelectric ceramic powder is loaded inside a die and a punch.

FIG. 3 is a diagram showing the electrical resistance between the electrodes immediately after performing the discharge plasma sintering process of Example 1 and the electrical resistance between the electrodes when performing the heating process.

FIG. 4 is a diagram showing the relationship between the maximum temperature and the pressurizing condition during the discharge plasma sintering process of Example 1 and the displacement obtained by the completed piezoelectric transducer.

FIG. 5 is a diagram showing the relationship between the highest temperature and the pressurizing condition during the discharge plasma sintering process of Example 1 and the bulk specific gravity of the completed piezoelectric transducer.

FIG. 6 is a view showing a test result of the breaking strength between the layers of the piezoelectric transducer of Example 1.

FIG. 7 is a diagram showing a bonding state between a holder and a piezoelectric conversion element used in a breaking strength test.

FIG. 8 is a diagram showing a test result of the breaking strength between the layers of the piezoelectric transducer of Example 2.

FIG. 9 is a view showing a test result of the breaking strength between the layers of the piezoelectric transducer of Example 3.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 discharge plasma sintering device 2 powder 3 die 4, 5 punch 4 a, 5 a extension 6, 7 electrode 8 vacuum chamber 9 a, 9 b cooling water channel 11 controller 12 pressurizing mechanism 13 sintering power supply 14 atmosphere control mechanism 15 cooling Mechanism 21, 22, 25 Carbon paper 23 PZT layer 24 Electrode layer

Claims (6)

[Claims] 1. A piezoelectric material and an electrode material are alternately laminated,
A laminated piezoelectric conversion element characterized by being sintered by an electric current sintering method at a temperature of 850 ° C. or more and less than 1100 ° C. while applying a pressure exceeding 5 MPa while compressing to increase the adhesion between layers. 2. The piezoelectric material is a powder containing lead zirconate titanate or a green sheet using the powder.
The electrode material is a powder, foil, or conductive paste containing at least one selected from platinum, palladium, and nickel, and the temperature is raised to 85 while applying a pressure exceeding 5 MPa.
2. Sintering by a current sintering method at a temperature of 900.degree. C. to 1000.degree. C. while applying a pressure of 0.degree. C. to less than 1100.degree. C., preferably more than 10 MPa.
The multilayer piezoelectric transducer according to any one of the preceding claims. 3. The multi-layer piezoelectric conversion element according to claim 1, wherein the electric current sintering method is a discharge plasma sintering method. 4. A piezoelectric material and an electrode material are alternately laminated,
In a state where the adhesion between the layers is increased by compression, the temperature is 850 ° C. or more and less than 1100 ° C. while applying a pressure exceeding 5 MPa, and preferably 900 ° C. or more and 1000 ° C. or less while applying a pressure exceeding 10 MPa. A method for manufacturing a laminated piezoelectric transducer, comprising sintering by a method and cooling to room temperature. 5. A powder containing lead zirconate titanate as a piezoelectric material or a green sheet using the powder, and a powder or foil containing at least one kind of electrode material selected from platinum, palladium and nickel. Or a conductive paste, after sintering at a temperature of 850 ° C. to less than 1100 ° C. while applying a pressure exceeding 5 MPa, preferably at a temperature of 900 ° C. or more and 1000 ° C. or less while applying a pressure exceeding 10 MPa. 5. The method according to claim 4, wherein cooling is performed to room temperature. 6. The method according to claim 4, wherein the electric current sintering method is a discharge plasma sintering method.