JP2003282993A - Polarizing method of laminated piezoelectric member and laminated piezoelectric member polarized by the polarizing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing method of a laminated piezoelectric member wherein deformation of a laminated piezoelectric member which remains after polarization is reduced and generation of crack and cut can be reduced. <P>SOLUTION: In the laminated piezoelectric member 1A, at least two layers of piezoelectric ceramics layers 2, 3 are laminated by inserting an internal electrode 6 between the layers 2, 3, and external electrodes 4, 5 are arranged on a main surface and a main back surface. In a polarizing method wherein the two outside piezoelectric ceramics layers 2, 3 are polarized in the thickness direction and in the same direction, a second DC electric field E2 is applied between the internal electrode 6 and the other external electrode 5, simultaneously with applying a first DC electric field E1 between one of the external electrodes 4 and the internal electrode 6 in such a manner that the internal electrode 6 has a ground potential, one of the external electrodes 4 has a positive potential and the other external electrode 5 has a negative potential. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polarizing a laminated piezoelectric material used in a piezoelectric electroacoustic transducer such as a piezoelectric receiver, a piezoelectric sounder, a piezoelectric speaker, and a piezoelectric buzzer.

[0002]

2. Description of the Related Art Conventionally, piezoelectric electroacoustic transducers such as piezoelectric receivers and buzzers use a unimorph type diaphragm in which a circular metal plate is attached to one side of a circular piezoelectric ceramic plate, and the periphery of the diaphragm is used. Supported in a circular case,
Generally, the case has a structure in which the opening is closed by a cover. However, in the case of a unimorph type diaphragm, since a ceramic plate whose outer diameter expands and contracts when a voltage is applied is adhered to a metal plate that does not change in size to obtain flexural vibration, the displacement amount, that is, the sound pressure is small. is there.

On the other hand, a bimorph type diaphragm having a laminated structure composed of a plurality of piezoelectric ceramic layers has been proposed (JP 2001-95094 A, JP 2002-1 A).
No. 0393). This vibration plate is a laminated piezoelectric body in which two or more piezoelectric ceramic layers are laminated with an internal electrode in between, and external electrodes are provided on the front and back main surfaces, and at least two outer piezoelectric ceramic layers are provided. It is polarized in the thickness direction and in the same direction. By applying an alternating signal between the external electrode and the internal electrode, the laminated piezoelectric body can be flexurally vibrated as a whole. In this case, by vibrating the first and second vibrating regions sequentially arranged in the thickness direction in mutually opposite directions, a larger displacement amount, that is, a larger sound pressure can be obtained as compared with the unimorph type.

[0004]

FIG. 8 shows a general method for polarizing the laminated piezoelectric material 20. By applying the DC voltage E between the external electrodes 21 and 22 on the front and back of the laminated piezoelectric body 20, the laminated piezoelectric body 20 is polarized in the same direction in the thickness direction. Deformation (warping) of the laminated piezoelectric body 20 that occurs during polarization causes the laminated piezoelectric body 20 to be a pressing jig 3 made of a conductor.
It is suppressed by pressurizing between 0 and 31.

However, in the polarization method as described above, when the piezoelectric body 20 is thinned to improve the sound pressure, the piezoelectric body 2 is
Deformation of 0 is promoted in inverse proportion to the decrease in thickness, 20 mm
In the case of the piezoelectric body 1 having a size of × 30 mm × 0.04 mm,
As shown in FIG. 9, the warp reaches several mm. Further, even when pressure polarization is performed by the pressure jigs 30 and 31, a large deformation remains in the piezoelectric body 20 after polarization. Further, although the deformation is forcibly suppressed by the pressure jigs 30 and 31 despite the abnormally large deformation occurring during polarization, a very large load is applied to the piezoelectric body 20 and cracks or chips are generated. There is a problem that it will end up. In particular, when the thickness of the piezoelectric body 20 is reduced to 50 μm or less, the crack / chip defect rate becomes extremely high.

Therefore, an object of the present invention is to provide a method for polarizing a laminated piezoelectric material which can reduce the deformation of the laminated piezoelectric material remaining after polarization and the occurrence of cracks and chips.

[0007]

In order to achieve the above object, the invention according to claim 1 laminates two or more piezoelectric ceramic layers with internal electrodes in between, and external electrodes on the front and back main surfaces thereof. In the polarization method of polarizing at least two piezoelectric ceramic layers on the outer side in the thickness direction and in the same direction, the internal electrode is ground potential, one external electrode is positive potential, and the other is A first DC electric field is applied between the one external electrode and the internal electrode so that the external electrode has a negative potential, and at the same time, a second DC electric field is applied between the internal electrode and the other external electrode. There is provided a method for polarizing a laminated piezoelectric material characterized by applying a voltage.

According to a fourth aspect of the present invention, there is provided a laminated piezoelectric body in which two or more piezoelectric ceramic layers are laminated with internal electrodes interposed therebetween, and external electrodes are provided on the front and back main surfaces thereof. The first DC electric field is applied between the one external electrode and the internal electrode so that the internal electrode has a ground potential, one external electrode has a positive potential, and the other external electrode has a negative potential. A laminated piezoelectric body characterized in that a second DC electric field is applied between the electrode and the other external electrode, and the two outer piezoelectric ceramic layers are polarized in the thickness direction and in the same direction.

In the polarization method of the present invention, instead of applying a DC electric field between the front and back external electrodes, an electric field is individually applied to each piezoelectric ceramic layer for polarization. For example, in the case of a laminated piezoelectric body having two piezoelectric ceramic layers, the insulation resistance of each layer varies due to the influence of the internal electrodes, and especially when a thin ceramic layer is used, the variation of each layer becomes significant. Therefore, when a DC electric field is applied between the front and back external electrodes as in the conventional case, a biased voltage is applied to one layer, which causes warpage. In the present invention, since an electric field is applied to each layer individually, the voltages applied to each layer are substantially the same even if the insulation resistance of each layer varies.
Moreover, since the two layers are polarized at the same time, the two layers can be balanced. Therefore, not only residual deformation can be reduced, but also deformation during polarization can be suppressed.

According to a second aspect of the present invention, the thickness of the laminated piezoelectric material is 5
When the thickness is 0 μm or less, the effect of the present invention becomes remarkable.
When the thickness is thicker than 50 μm, the variation of the insulation resistance of each layer due to the internal electrodes is relatively small, but in the case of the laminated piezoelectric body having the thickness of 50 μm or less, the variation of the insulation resistance of each layer becomes very large. It becomes about several tens of times. Therefore, the deformation of such a laminated piezoelectric material having a thin layer becomes extremely large when polarized.

As described in claim 3, it is desirable to apply the DC electric field while applying pressure to both main surfaces of the laminated piezoelectric material in opposite directions. Although it is possible to polarize the laminated piezoelectric material without applying pressure, the amount of residual deformation can be reduced to a fraction of that when no pressure is applied. Further, in the present invention, since the deformation during polarization is small, it is possible to reduce the cracking or chipping of the piezoelectric body due to the pressurization.

The laminated piezoelectric material of the present invention is not limited to the two-layer structure and may have three or more layers. For example, in the case of a three-layer structure, the intermediate layer sandwiched by the internal electrodes is a non-polarized dummy layer. In the case of a three-layer structure, the intermediate layer may be thicker than the outer two layers. In this case, since the outer two layers can be thinned, a larger displacement amount can be obtained even with the same voltage, and a larger sound pressure can be obtained.

[0013]

1 shows an example of a laminated piezoelectric material according to the present invention. The laminated piezoelectric body 1 of the present embodiment is used as a diaphragm of a piezoelectric electroacoustic transducer that utilizes bending vibration. The laminated piezoelectric body 1 is formed by laminating two PZT-based piezoelectric ceramic layers 2 and 3, and external electrodes 4 and 5 are formed on the front and back main surfaces of the laminated piezoelectric body 1 to form the ceramic layers 2 and 3. An internal electrode 6 is formed between them.
The two ceramic layers 2 and 3 are polarized in the same direction in the thickness direction as indicated by an arrow P in FIG. On the end face of the laminated piezoelectric body 1, an end face electrode 7 for connecting the external electrodes 4 and 5 and an end face electrode 8 for pulling out the internal electrode 6 to the outside.
And are formed.

In the laminated piezoelectric body 1 having the above structure, when an alternating voltage is applied between the external electrodes 4, 5 and the internal electrode 6,
The electric field directions acting on the front and back ceramic layers 2 and 3 are opposite to each other in the thickness direction. On the other hand, the polarization directions of both ceramic layers 2 and 3 are the same in the thickness direction. Piezoelectric ceramics have the property of contracting in the plane direction if the polarization direction and the electric field direction are the same direction, and have the property of expanding in the plane direction if the polarization direction and the electric field direction are opposite. Therefore, if an alternating voltage is applied as described above,
When one ceramic layer expands, the other ceramic layer contracts, and the laminated body 1 as a whole causes periodic bending vibration. Since this displacement amount is larger than that of the unimorph type diaphragm, the sound pressure also increases.

The laminated piezoelectric material 1 is manufactured as follows. First, a green sheet of piezoelectric ceramics to be the back side ceramics layer 3 is prepared, and a conductive paste 6 to be an internal electrode is applied to one side thereof, and then the front side ceramics layer 2 is formed.
The green sheets of piezoelectric ceramics are laminated.
The printed pattern of the conductive paste 6 is, for example, as shown in FIG. Then, about 1100 this laminated body
Baked integrally at ° C, length x width x thickness = 20 mm x 30 m
A piezoelectric body unit 1A of m × 0.040 mm was obtained. After firing, external electrodes 4 and 5 are formed on the front and back surfaces of the piezoelectric body unit 1A by a thin film forming method as shown in FIG. 2B, and lead electrodes 6a ( (See FIG. 3).

Next, using the external electrodes 4 and 5 and the extraction electrode 6a of the internal electrode 6, as shown in FIG.
Direct current electric fields E1 and E2 were individually applied to each layer of A to perform polarization treatment. Specifically, the positive side of the power source E1 is connected to one external electrode 4, the negative side of the power source E2 is connected to the other external electrode 5, and the negative side of the power source E1 and the positive side of the power source E2 are connected to the internal electrode 6. It was connected to the ground together with the connected extraction electrode 6a. Then, the piezoelectric unit 1A was polarized while pressing the entire surface of the piezoelectric unit 1A using the pressing jigs 10 and 11. As shown in FIG. 4, the polarization condition of the ceramic layer 2 on the front side is as follows: ramp time to maximum voltage: 60 sec, electric field: 2.50 kV
/ Mm (50 V / 20 μm), holding time × holding temperature = 3
It was kept constant at 0 sec × 50 ° C. On the other hand, the polarization condition of the ceramic layer 3 on the back side is that the inclination time to the maximum voltage is 60:
sec, electric field: −2.5 kV / mm (50 V / 20 μ
m), holding time × holding temperature = 30 sec × 50 ° C. The pressure jigs 10 and 11 are about 15 g / cm ²
Was added. After cutting out the polarized piezoelectric unit 1A into elements, an end face electrode 7 for connecting the external electrodes 4 and 5 and an end face electrode 8 for drawing out the internal electrode 6 to the outside are formed on the end face, The laminated piezoelectric material 1 shown in FIG.

On the other hand, as a comparative example, a laminated piezoelectric material was manufactured by the following method. First, a green sheet of piezoelectric ceramics was prepared, a conductive paste was applied to one surface of the green sheet in the same printing pattern as in FIG. 2A, and then unprinted green sheets were laminated. This stack is about 110
Integrally baked at 0 ° C, 20mm × 30mm × 0.04
A 0 mm piezoelectric unit was obtained. After firing, external electrodes 4 and 5 were formed on the front and back surfaces of the piezoelectric unit by a thin film forming method. Next, using the external electrodes 4 and 5, a DC electric field E was applied to the entire piezoelectric unit to perform polarization treatment, as in FIG. The polarization condition is a ramp time to the maximum voltage: 60 se
c, electric field: 2.50 kV / mm (100 V / 40 μ
m), holding time × holding temperature = 30 sec × 50 ° C. In addition, about 15 g / c between the pressing jigs 30 and 31
A load of m ² was applied and pressure was applied. After cutting out the polarized piezoelectric unit into elements, an end face electrode 7 for connecting the external electrodes 4 and 5 and an end face electrode 8 for pulling out the internal electrode 6 to the outside are formed on the end face thereof. A laminated piezoelectric material 1 similar to that was obtained.

FIG. 5 shows the measured amount of residual warpage of the unit after polarization. In the present invention, 0.08 to 0.57 m
It was distributed in the range of m, and the average amount of warpage was 0.26 mm. On the other hand, in the comparative example, the particles were distributed in the range of 0.15 to 1.40 mm and the average warpage amount was 0.63 mm. As is clear from the above results, the amount of residual warpage after polarization by the method of the present invention is reduced to about 1/3 of that of the comparative example. In order to prevent defects in the finished product process as an element, the amount of warp in the element must be 0.2 mm or less, that is, the amount of warp in the unit must be 0.60 mm or less. In the present invention, almost all of the products were non-defective, but in the comparative example, about 50% were defective.

FIG. 5 shows a comparison of residual warpage after polarization is performed with the entire surface of the piezoelectric unit pressed by a pressing jig. The amount of deformation of the piezoelectric unit during polarization is obtained. Therefore, FIG. 6 shows a change in the warp amount of the unit in a substantially free state. FIG. 6 shows changes in warpage during polarization between the method of the present invention and the comparative example by the conventional method. The measurement temperature is 50 ° C. In the method of the present invention, 8
A weight g of g was placed in the center of the unit, a voltage was applied to each of the two layers up to 50 V with an inclination of 60 sec, and the maximum warpage at equal intervals (8 points) was sequentially measured. Then, the maximum voltage was maintained at 50 V for 30 seconds, and the warpage was measured. Then, the voltage was removed and the amount of residual warpage was measured. On the other hand, also in the conventional method, similarly, a positioning weight of 8 g is arranged in the central part of the unit, and the voltage is simultaneously applied to two layers at 100 V for 60 seconds.
It was applied with an inclination of ec, and the maximum warpage at equal intervals (8 points) was sequentially measured. And 30s at maximum voltage 100V
ec was held and the warpage was measured. Then, the voltage was removed and the amount of residual warpage was measured. The horizontal axis of FIG. 6 is the voltage per layer in the present invention, and is the total voltage of the two layers in the comparative example. Therefore, 50V in the present invention is 1 of Comparative Example.
It corresponds to 00V.

As is apparent from FIG. 6, in the present invention, 10
~ 25V produces a maximum warpage of about 2 mm. However, increasing the voltage further does not increase the warpage. Under the condition where the voltage is removed, there is a residual sled of about 0.5 mm. On the other hand, in the case of the comparative example, the amount of warpage simply increases as the voltage increases, and a maximum warpage of about 5 mm occurs at 100V. Also, the amount of warpage varies greatly among samples. Under the condition where the voltage is removed, a large warp of about 3 mm remains. From the above results, it is understood that the deformation amount during polarization is smaller in the method of the present invention than in the conventional method. Therefore, even if the pressing jigs 10 and 11 are forcibly pressed during polarization, the load applied to the piezoelectric body unit 1A is small and cracks and chips can be reduced. In addition, compared with the case where no pressure is applied,
The residual sled could be reduced to about half.

In the above embodiment, the power source E1 for applying a DC electric field to the front ceramic layer 2 and the back ceramic layer 3 are used.
The same voltage (50V) as the power source E2 that applies a DC electric field to the
However, the insulation resistance ratio of both ceramic layers 2 and 3 is measured in advance, and the power source E is determined according to the insulation resistance ratio.
The voltage ratio of 1 and E2 may be adjusted. In this case,
The amount of deformation of the laminated piezoelectric body can be further reduced.

FIG. 7 shows a second embodiment of the method for polarizing the laminated piezoelectric material according to the present invention. This example shows a polarization method of a laminated piezoelectric body 1'having a three-layer structure. Internal electrodes 6b, 6c are provided between the ceramic layers 2a, 2b, 2c.
And external electrodes 4 and 5 are formed on the front and back main surfaces. The plus side of the power source E1 is connected to the external electrode 4, the minus side of the power source E2 is connected to the external electrode 5, and the minus side of the power source E1 and the plus side of the power source E2 are connected to the internal electrodes 6b and 6c. When it is connected to the ground together with it, the two outer ceramic layers 2a and 2c are polarized in the same direction in the thickness direction as shown by an arrow P. In addition,
The intermediate layer 2b sandwiched between the internal electrodes 6b and 6c becomes a dummy layer which is not polarized.

In the case of the three-layer structure, the outer two layers 2a and 2c can be made thinner than in the case of the two-layer structure, while the thickness required for the strength of the piezoelectric body 1'is secured, so that the same voltage is applied. Even if a large displacement amount of the piezoelectric body 1'is obtained,
Greater sound pressure can be obtained. Of the three layers, the intermediate layer 2b may have the same thickness as the outer two layers 2a and 2b, or may have a larger thickness. When the thickness is increased, the thickness of the outer two layers 2a and 2b can be further reduced.

The present invention is not limited to the above embodiments, but various modifications can be made without departing from the spirit of the present invention. In the above embodiment, an example of the structure in which the piezoelectric ceramic layer has two layers or three layers has been described, but it may have four or more layers. However, at the time of polarization, all the internal electrodes are connected to the ground, so that all layers except the outer two layers are dummy layers that are not polarized. In the above-described embodiment, the end face electrode that is electrically connected to the internal electrode is formed on the end face of the laminated piezoelectric body, and the end face electrode is drawn out to the outside through the end face electrode, but the present invention is not limited to this. That is, the internal electrodes may be drawn out through the through holes as in JP-A-61-205100, or may be drawn out through the slit-shaped grooves or holes. In the method for manufacturing the laminated piezoelectric body of the above-mentioned embodiment, the ceramic green sheets are laminated via the electrode film, the laminated body is simultaneously fired to obtain a sintered laminated body, and then the sintered laminated body is polarized. Instead of this method, two or more piezoelectric ceramic plates that have been fired in advance may be laminated and adhered, and then the polarization treatment may be performed. However, the former manufacturing method in which firing is performed after lamination can significantly reduce the thickness of the piezoelectric body and increase the sound pressure as compared with the latter method in which firing is performed in advance, so vibration with excellent acoustic conversion efficiency can be achieved. It is possible to obtain a plate. The laminated piezoelectric material of the present invention is
The piezoelectric sheet is not limited to being composed of only the piezoelectric ceramic layer, and a reinforcing sheet such as a resin film may be attached to one surface or both surfaces of the piezoelectric body. However, unlike the metal plate of the unimorph type diaphragm, this reinforcing sheet is for preventing cracks and the like of the laminate, and is preferably one that does not hinder the flexural vibration of the laminate.

[0025]

As is apparent from the above description, claim 1
According to the invention of claim 2, the piezoelectric ceramic layer is formed by laminating two or more piezoelectric ceramic layers with the internal electrodes in between, and the external electrodes are provided on the front and back main surfaces thereof. A first DC electric field is applied between one external electrode and the internal electrode so that the electrode has a positive potential and the other external electrode has a negative potential, and at the same time, a first DC electric field is applied between the internal electrode and the other external electrode. By applying a DC electric field of 2, the two outer piezoelectric ceramic layers are polarized in the thickness direction and in the same direction, so compared with the conventional method of applying an electric field between external electrodes, The deformation of the laminated piezoelectric material remaining after polarization can be reduced, and a laminated piezoelectric material of good quality can be obtained. In addition, in the present invention, since an electric field is applied to each layer individually, deformation during polarization can be suppressed, and cracking or chipping of the piezoelectric body due to pressure can be reduced. Therefore, the amount of residual deformation can be reduced to a fraction of that when no pressure is applied.

[Brief description of drawings]

FIG. 1 is a sectional view of a first embodiment of a laminated piezoelectric material according to the present invention.

FIG. 2 is a pattern diagram of internal electrodes and external electrodes.

FIG. 3 is a diagram showing a polarization method of the laminated piezoelectric material shown in FIG.

FIG. 4 is a voltage application profile diagram during polarization.

FIG. 5 is a distribution chart of residual warpage after polarization of the present invention and a comparative conventional example.

FIG. 6 is a voltage-warpage amount change diagram during non-pressure polarization of the present invention and a comparative conventional example.

FIG. 7 is a diagram showing a polarization method of a second embodiment of the laminated piezoelectric material according to the present invention.

FIG. 8 is a diagram showing a conventional method for polarizing a laminated piezoelectric material.

FIG. 9 is a diagram showing residual warpage of a conventional laminated piezoelectric material.

[Explanation of symbols]

1A Piezoelectric unit 1,1 'laminated piezoelectric body 2,3,2a to 2c Ceramics layer 4, 5 External electrode 6,6b, 6c Internal electrodes E1, E2 DC power supply 10,11 Pressure jig

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kiyama Iyama             Stock number 2 26-10 Tenjin, Nagaokakyo-shi, Kyoto             Murata Manufacturing Co., Ltd. (72) Inventor Yoshimasa Yoshimasa             Stock number 2 26-10 Tenjin, Nagaokakyo-shi, Kyoto             Murata Manufacturing Co., Ltd.

Claims (4)

[Claims] 1. A laminated piezoelectric body in which two or more piezoelectric ceramic layers are laminated with an internal electrode interposed therebetween, and external electrodes are provided on the front and back main surfaces thereof, and at least two outer piezoelectric ceramic layers are provided. In the polarization method of polarizing in the thickness direction and in the same direction, the one external electrode and the internal electrode are so arranged that the internal electrode has a ground potential, one external electrode has a positive potential, and the other external electrode has a negative potential. A method for polarizing a laminated piezoelectric material, characterized in that a second DC electric field is applied between the internal electrode and the other external electrode at the same time as applying a first DC electric field therebetween. 2. The polarization method for a laminated piezoelectric material according to claim 1, wherein the thickness of the laminated piezoelectric material is 50 μm or less. 3. The method for polarizing a laminated piezoelectric material according to claim 1, wherein the application of the DC electric field is performed while pressing both main surfaces of the laminated piezoelectric material in opposite directions. 4. A laminated piezoelectric body in which two or more piezoelectric ceramic layers are laminated with an internal electrode interposed therebetween, and external electrodes are provided on the front and back main surfaces thereof, wherein the internal electrode is ground potential and one external A first DC electric field is applied between the one external electrode and the internal electrode so that the electrode has a positive potential and the other external electrode has a negative potential, and at the same time, between the internal electrode and the other external electrode. A laminated piezoelectric body characterized in that a second DC electric field is applied to the two outermost piezoelectric ceramic layers to polarize in the thickness direction and in the same direction.