JP3144376B2 - Piezoelectric transformer and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer used for a power supply circuit for lighting a cold cathode fluorescent tube or the like and various high voltage generation power supply circuits, and particularly requires a small size, high efficiency, high voltage step-up and high reliability. And a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a power supply for lighting a cold-cathode fluorescent tube, a deflection device for a television, and a charging device for a copying machine, which requires a high voltage, is used in a backlight for a liquid crystal. In the circuit, a wire-wound electromagnetic transformer has been used as a high-voltage generating transformer. The electromagnetic transformer has a structure in which a conductor is wound around a magnetic core, and in order to achieve a high transformation ratio, it is necessary to increase the number of conductors to be wound. Therefore, it is very difficult to realize a compact and highly efficient electromagnetic transformer.

Therefore, a piezoelectric transformer using the piezoelectric effect has been proposed. FIG. 6 is a perspective view showing a symmetric third-order Rosen multilayer piezoelectric transformer disclosed in Japanese Patent Application Laid-Open No. 6-224484, which is one of typical piezoelectric transformers.

A symmetric tertiary Rosen multilayer piezoelectric transformer disclosed in Japanese Patent Application Laid-Open No. 6-224484 shown in FIG. 6 has a long plate-shaped piezoelectric body 610 extending in a longitudinal direction, and a driving section 61L and a power generation section 6 are provided.
2. It is divided into three driving units 61R. Drive unit 61
L and 61R are the piezoelectric ceramic layer 611 and the internal electrode layer 6
12 are alternately stacked in a plurality, and external electrodes 614 are provided on both upper and lower surfaces of each of the driving units 61L and 61R.
(One external electrode 615 is not shown).

When a cross section perpendicular to the length direction of the piezoelectric body 610 is viewed, odd-numbered internal electrode layers are exposed on the right side surface of the piezoelectric body 610, and even-numbered internal electrode layers are exposed on the left side surface. as such, more as it engages the teeth of the two comb
Each of them is alternately exposed to two side surfaces of the piezoelectric body 610.

[0006] Connection electrodes 616 provided on both side surfaces of the piezoelectric body 610 (one connection electrode is not shown).
Are the internal electrode layer 612 and the electrodes 614, 6 on both the upper and lower surfaces.
15 respectively.

On the other hand, the power generation section 62 is located at the center in the length direction of the piezoelectric body 610, and has a band-shaped electrode 618a extending in the width direction (the inside band-shaped electrode 618b is not shown) on its surface and inside. The left and right portions sandwiching the electrodes 618a and 618b are polarized in opposite directions in the length direction.

In driving the piezoelectric transformer shown in FIG. 6, electrodes 61 on the upper surfaces of two driving units 61L and 61R are used.
4 is connected to the input terminal 619, and the electrode 615 on the lower surface is connected.
Connect to output terminal 620. Further, the strip electrode 618 a of the power generation unit 62 is connected to the output terminal 621.

An AC voltage is externally applied between the two terminals 619 and 620 to cause the piezoelectric body 610 to vibrate in the length direction. Then, the external electrodes 6 of the driving units 61L and 61R are applied to the power generation unit 62 in accordance with the longitudinal vibration of the piezoelectric body 610.
A boosted voltage is generated between the internal electrodes 614 and 615 and the internal electrodes 612 and the surface electrodes 618 a and the internal electrodes 618 b of the power generation unit 62.

In manufacturing the piezoelectric transformer shown in FIG. 6, a green sheet laminating method is used. That is, a green sheet of piezoelectric ceramics is formed, and the internal electrodes 6 are formed in a predetermined pattern using Ag / Pd electrodes.
Print electrodes 12 and 618b. After laminating a predetermined number of green sheets on which the internal electrodes are formed,
A laminate is formed by hot pressing, and the laminate is fired to obtain a sintered body. The external electrodes 6 of the driving units 61L and 61R are provided on the surface of the sintered body.
14, 615 and the electrodes to be the surface electrodes 618a of the power generation unit 62 are formed by printing and firing to obtain a piezoelectric transformer.

[0011] In this manufacturing process, in the firing process of the laminate, the laminate is placed on a setter (bedboard), put into a firing furnace, and fired. At this time, the firing atmosphere is slightly different between the setter side and the opposite side of the laminated body due to the packing effect of the setter, and the progress of firing is shifted between the setter side and the opposite side. Therefore, there is a problem that the sintered body is warped.

Although not a method of manufacturing a piezoelectric transformer,
Techniques for preventing warpage of a sintered body when firing a laminate are disclosed in JP-A-3-232775 and JP-A-6-3-3.
No. 26470 and JP-A-7-38258. These are shown below.

FIG. 7 shows a technique disclosed in Japanese Patent Application Laid-Open No. 3-232775. In FIG. 7, reference numeral 71 denotes a ceramic substrate made of a green sheet, 72 denotes a dummy green sheet placed on the ceramic substrate 71, and
Reference numeral 3 denotes a firing jig (setter) on which the ceramic substrate 71 is placed.

In the technique shown in FIG.
The green sheet 72 placed on the ceramic substrate 71
Does not sinter.

FIG. 8 shows a technique disclosed in Japanese Patent Application Laid-Open No. 6-326470. 8, 81 is a green sheet laminate, 82 is an electrode pattern, 83 is a via electrode, 84 is a non-sintered layer, 85 is an alumina layer for joining, and 86 is a bottom plate.

The technique disclosed in Japanese Patent Application Laid-Open No. 7-38258 relates to a method for manufacturing a multilayer ceramic substrate similarly to the above-mentioned Japanese Patent Application Laid-Open No. 6-326470. The sintered material is placed on the uppermost layer and the lowermost layer to prevent warpage.

[0017]

However, as described with reference to the method of manufacturing the symmetric tertiary Rosen multilayer piezoelectric transformer shown in FIG. 6, the multilayer piezoelectric transformer is manufactured by using a green sheet laminating method, and In the body firing process, the laminate is placed on a setter and put into a firing furnace for firing.At this time, the firing atmosphere on the setter side and the opposite side of the laminate is affected by the packing effect of the setter. There is a problem that the progress of sintering is slightly different between the setter side and the opposite side, and the sintered body is warped.

Further, FIG.
In the technology disclosed in Japanese Patent Laid-Open Publication No. H10-209, as a cause of the warpage of the ceramic substrate, from the influence of heat radiation on the upper side of the ceramic substrate,
It is considered that a temperature difference is generated between the ceramic substrate and a difference in thermal expansion and contraction during sintering, and that warpage occurs.In the present invention, as a cause of warpage of the sintered body, Considering that the temperature difference between the ceramic substrate and the ceramic substrate occurs due to the influence of heat radiation on the upper side of the ceramic substrate, and that the warpage occurs due to the difference in thermal expansion and contraction at the time of sintering. Therefore, the dummy green sheet is placed on the upper side of the ceramic substrate, and the technique shown in FIG. 7 cannot be directly applied to the present invention.

Further, in the technique shown in FIG. 7, a method of covering a dummy green sheet is used for the purpose of alleviating a difference in heat radiation, but the composition (thickness, shape, etc.) of the dummy sheet to be used is not specified. That is, if a dummy sheet is used to reduce the difference in heat radiation, the heat capacity of the dummy sheet has no effect unless a sheet having a large composition is used. The numbers have to be adjusted precisely, but this is not disclosed.

FIG. 8 shows a Japanese Patent Application Laid-Open No. 6-326470.
In the technique disclosed in Japanese Patent Application Laid-Open No. 7-38258, the influence of shrinkage in the planar direction is considered as a cause of warpage of the ceramic substrate, and the unsintered layer is adhered to suppress the shrinkage. However, this mechanically suppresses sintering shrinkage, and it is impossible to apply the technique shown in FIG. 8 to the present invention.

In the technique shown in FIG. 8, since the unsintered layer is a layer that does not react during firing, it is considered that the adhesion to the ceramic substrate is not so large. There is the problem of compositional effects at the boundaries of different materials.

An object of the present invention is to provide a piezoelectric transformer having improved transformer characteristics and reliability by suppressing the occurrence of warpage, and a method of manufacturing the same.

[0023]

In order to achieve the above object, a piezoelectric transformer according to the present invention is a piezoelectric transformer formed by laminating a lead-based piezoelectric material layer and an electrode, wherein the piezoelectric material is a first piezoelectric body located on the side to be placed on the firing jig upon firing, the laminated on said first piezoelectric on
Consists of a second piezoelectric, the particle diameter of the second piezoelectric body is smaller than the particle diameter of the first piezoelectric body.

The particle size of the first piezoelectric body is 5 to 6 μm.
And the particle size of the second piezoelectric body is 2 to 3 μm.

The piezoelectric body has an input electrode and an output electrode provided on side surfaces of the first and second piezoelectric bodies.

The piezoelectric body is obtained by polishing and removing the second piezoelectric body and providing input and output electrodes on upper and lower surfaces.

Further manufacturing method of a piezoelectric transformer according to the present invention, there is provided a piezoelectric transformer manufacturing method using a green sheet laminating method, the green sheet to be the first piezoelectric,
A green sheet serving as a second piezoelectric body is laminated to form a layer structure, and a ceramic particle size of the green sheet serving as the second piezoelectric body is smaller than a ceramic particle size of the green sheet serving as the first piezoelectric body. The green sheet to be the first piezoelectric body is placed on a firing jig and fired.

[0028] Also after the firing of the green sheet, the first
And a step of polishing and removing the second piezoelectric body.

[0029]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a perspective view showing a piezoelectric transformer according to Embodiment 1 of the present invention, and FIGS.
FIG. 2 is a cross-sectional view illustrating a stacked structure of a driving unit and a power generation unit in the piezoelectric transformer according to the first embodiment of the present invention.

As shown in FIG. 1, the piezoelectric body 100 used in the piezoelectric transformer according to the first embodiment of the present invention is formed in a long plate shape, and the driving unit 101, the power generation unit 108, The driving section 102 is divided into three sections.

In FIG. 1, the driving units 101 and 102
The drive units 101 and 102 are for applying an input voltage to vibrate the piezoelectric transformer. The drive units 101 and 102 include input electrodes 103 and 104 (see FIG. 2) formed on side surfaces and an input electrode 105 (see FIG. 2) formed on a lower surface. 2) and the input internal electrode 10
6,107.

The power generation unit 108 includes the driving units 101 and 1
02 is for generating a boosted voltage by vibrating based on the vibration of 02. The power generation unit 108 includes output electrodes 109 and 110 (see FIG. 3) formed on the side surfaces and an output electrode formed on the lower surface. The electrode 111 (see FIG. 3) and the output internal electrode 112
(See FIG. 3).

As shown in FIGS. 1, 2 and 3, a piezoelectric body 100 used in the piezoelectric transformer according to the first embodiment of the present invention
Is located on the side to be placed on the firing jig during firing .
The piezoelectric element 116 includes a first (hereinafter referred to as a base layer) piezoelectric body 116 and a second (hereinafter referred to as a surface layer) piezoelectric body 117 laminated on the base layer piezoelectric body 116.

Further, the lower side 201 of the piezoelectric body 100
5A is a surface side in contact with a setter (sintering jig) 401 during sintering shown in FIG. 5A, and a surface-side piezoelectric body 117 located on the upper side 202.
Are stacked on the base piezoelectric member 116 during sintering, and are integrated with the piezoelectric member 116 by sintering.

Further, the surface piezoelectric member 117 is made of ceramic having a particle diameter smaller than the ceramic particle diameter used for the base layer piezoelectric member 116. Then, after sintering, the excess thickness of the surface piezoelectric member 117 is polished, and the sintered body of the polished piezoelectric member 117 and piezoelectric member 116 is used as the piezoelectric member 100 of the piezoelectric transformer.

In firing the lead-based piezoelectric material,
It is generally known that the atmosphere of lead during sintering affects the progress of sintering of the piezoelectric body. If the concentration of the atmosphere of lead is insufficient, sintering becomes difficult and the growth of crystal grains is suppressed. Is done.

This means that when the concentration of lead in the atmosphere is insufficient, the lead in the piezoelectric body sublimates and scatters as lead vapor,
Since the lead in the laminate is in a poor (insufficient) state, it means that sintering is difficult to proceed and growth of crystal grains is suppressed.

When the laminate 400 is placed on the setter 401 and baked as shown in FIG. 5A, the surface of the laminate 400 on the setter 400 side (A side) and the opposite side (B side) When the surface A is compared with the surface A, since the setter 401 is present, the scattering of lead from the surface A is suppressed (the packing effect). However, since the surface B is free, Depending on the state of the lead atmosphere, lead in the piezoelectric body is scattered and lead to a poor state, and the crystal grows on the side A, whereas the crystal growth is suppressed on the side B. Therefore, imbalance occurs in the progress of sintering, and the sintered body is warped as shown in FIG.

Therefore, in the first embodiment of the present invention, the particle size of the piezoelectric body 117 used for the layer on the B side is smaller than that of the piezoelectric body 116 on the A side. This makes it possible to lengthen the path in which lead sublimates and scatters,
Since the smaller the particle size, the faster the sintering proceeds, the amount of lead scattered from the B side can be suppressed, and the amount of lead scattered between the A side surface and the B side surface can be adjusted. It becomes possible to balance the progress of sintering, thereby reducing warpage.

In the driving state of the piezoelectric transformer according to the first embodiment of the present invention, the input electrodes 105 of the driving units 101 and 102 are driven.
And the input internal electrodes 106 and 107 are polarized in the thickness direction, and the power generation unit 108 outputs the output electrode 111 and the output internal electrode 112 and the input electrode 105 and the input internal electrode 10.
6 and 107 are polarized in the longitudinal direction.

The input electrodes 103 and 104 formed on the side of the piezoelectric transformer 100 are connected to input / output terminals 113 and 114, and the output electrode 109 formed on the side of the piezoelectric transformer 100 is connected to the output terminal 115. Connected. Then, an input voltage is applied between the two terminals 113 and 114 at a predetermined frequency, and the input terminal
A voltage boosted at the same frequency is generated between the output terminals 113.

(Example 1) Next, a description will be given using Example 1 which embodies Embodiment 1 of the present invention.

In the piezoelectric transformer of the present invention, Nepec 8 (manufactured by Tokin) was used as a piezoelectric ceramic material, but powder having an average particle size of 5 μm was used for the piezoelectric body 116 of the base layer, and averaged for the piezoelectric body 117 of the surface layer. A powder having a particle size of 2 μm was used.

First, each of these powders was formed into a slurry, and then a green sheet serving as the base piezoelectric member 116 was formed to have a thickness of 120 μm, and a green sheet serving as the surface piezoelectric member 117 was formed to have a thickness of 60 μm. .

Then, a green sheet in which an electrode serving as an internal electrode was formed by printing an electrode paste made of Ag / Pd (Ag / Pd ratio was 80/20) was formed on the green sheet serving as the piezoelectric body 116.

After cutting these green sheets into a predetermined size, one green sheet on which no electrodes are printed and one green sheet on which electrodes are printed are formed into one layer with the green sheet serving as the piezoelectric body 116 of the base layer. After laminating five layers, one green sheet to be the surface piezoelectric member 117 is laminated thereon, then put into a mold, and press pressure 100 kg /
After performing hot press molding under the conditions of cm ² and a temperature of 150 ° C., a green sheet to be the piezoelectric body 116 of the base layer is placed on a setter, and baked under the conditions of a peak temperature of 1100 ° C. and a keeping time of 20 minutes to obtain a laminate sintering. Formed body.

The warpage of the resulting laminated sintered body was 5
It was 0 μm or less.

Table 1 shows the results of confirming the warpage of the laminated sintered body by changing the particle size of the powder of the piezoelectric body used in the same manner as described above.

[0050]

[Table 1]

Next, after applying an Ag / Pd paste (Ag / Pd ratio is 85/15) in a predetermined pattern on the lower and side surfaces of the driving units 101 and 102 and the power generating unit 108, a peak temperature of 650 ° C. and a keeping time of Bake for 15 minutes,
Input electrode 103, 104, 105 and output electrode 10
Electrodes 9, 9, and 111 were formed.

Subsequently, the temperature was set to 150 ° C. using a polarization jig.
Electric field 2 kV / mm in silicone oil
0 minutes, the driving units 101 and 102 are moved in the thickness direction.
Then, the power generation unit 108 was polarized in the length direction.

With respect to the piezoelectric transformer of the present invention thus obtained, a voltage was applied with a resistance of 100 kΩ as a load, and the transformer characteristics were evaluated.
%, And a driving evaluation of 1000 hours (2
0), no failure occurred, and a piezoelectric transformer excellent in characteristics and reliability was obtained. However, when the transformer characteristics of a comparative product in which a large warp occurred were evaluated, the warp adversely affected the vibration of the piezoelectric transformer, and the conversion efficiency was reduced to 90%.

(Embodiment 2) FIG. 4 is a perspective view showing Embodiment 2 of the present invention.

The second embodiment of the present invention shown in FIG. 4 differs from the first embodiment shown in FIG. 1 in that the piezoelectric body 117 on the surface layer is polished and removed after the formation of the laminated sintered body, and the input electrodes are formed on the upper and lower surfaces of the piezoelectric body. 105a, 105b and output electrodes 111a, 111b
Is characterized by the fact that With such a configuration, the configuration is such that the piezoelectric body is more effectively used, and there is an advantage that the transformer characteristics can be improved.

(Embodiment 2) Next, a description will be given using Embodiment 2 which embodies Embodiment 2 of the present invention. In the second embodiment,
The thickness of the green sheet to be the surface piezoelectric member 117 is 12
The thickness is set to 0 μm, and one green sheet on which no electrode is printed and one green sheet on which the electrode is printed are stacked as a single layer, and five layers are stacked on the green sheet serving as the piezoelectric body 116 of the base layer, and then the electrodes are printed thereon. One green sheet that has not been stacked is further laminated, and a single green sheet that is to be the surface piezoelectric member 116 is further laminated thereon.

Next, in the same manner as in the first embodiment, a laminated sintered body is formed by hot pressing and firing, and the thickness of the surface piezoelectric material is polished by a lapping machine. 105a, 105b, 103, 104 (10
5b and 104 are not shown) and the output electrodes 111a, 1
Electrodes serving as 11b, 109, and 110 (111b and 110 are not shown) were formed to obtain a piezoelectric transformer of the present invention.

After the thus obtained piezoelectric transformer was polarized in the same manner as in Example 1, a voltage was applied with a load of 100 kΩ as a load, and the transformer characteristics were evaluated. The conversion efficiency was 97%. Higher results were obtained than in Example 1. In addition, the reliability was as good as in Example 1.

[0059]

As described above, according to the present invention, a piezoelectric transformer formed by laminating a layer made of a lead-based piezoelectric material and an electrode is placed on a sintering jig during firing. By setting the particle size of the piezoelectric material in the surface layer to be smaller than the particle size of the piezoelectric material in the base layer, the scattering state of lead on the piezoelectric material side of the base layer can be adjusted, and the firing on the surface layer side and the base layer side of the piezoelectric material can be adjusted. The progress can be balanced, the occurrence of warpage can be suppressed, and the transformer characteristics and reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a piezoelectric transformer according to Embodiment 1 of the present invention.

FIG. 2 is a cross-sectional view illustrating the piezoelectric transformer according to the first embodiment of the present invention, and is a cross-sectional view taken along line AA ′ of FIG.

FIG. 3 is a cross-sectional view showing the piezoelectric transformer according to the first embodiment of the present invention, which is a cross-sectional view taken along line BB ′ of FIG. 1;

FIG. 4 is a perspective view showing a piezoelectric transformer according to Embodiment 2 of the present invention.

FIG. 5 is a cross-sectional view illustrating a warped state.

FIG. 6 is a perspective view showing a piezoelectric transformer according to a conventional example.

FIG. 7 is a sectional view showing a piezoelectric transformer according to a conventional example.

FIG. 8 is a sectional view showing a piezoelectric transformer according to a conventional example.

[Description of Signs] 101, 102 Drive unit 103, 104, 105, 105a, 105b Input electrode 106, 107 Input internal electrode 108 Power generation unit 109, 110, 111, 111a, 111b Output electrode 112 Output internal electrode 113, 114 Input terminal 115 output terminal 116 base layer piezoelectric body 117 surface layer piezoelectric body 110 piezoelectric body

Claims (6)

(57) [Claims] 1. A piezoelectric transformer formed by laminating a layer of a lead-based piezoelectric material and an electrode, wherein the piezoelectric material is located on a surface placed on a firing jig during firing . the piezoelectric body consists of a second piezoelectric body is laminated on said first piezoelectric member, the particle diameter of the second piezoelectric body is smaller than the particle diameter of the first piezoelectric A piezoelectric transformer, characterized in that: 2. The piezoelectric transformer according to claim 1, wherein the particle size of the first piezoelectric body is 5 to 6 μm, and the particle size of the second piezoelectric body is 2 to 3 μm. 3. The piezoelectric transformer according to claim 1, wherein the piezoelectric body has an input electrode and an output electrode provided on side surfaces of the first and second piezoelectric bodies. 4. The piezoelectric transformer according to claim 1, wherein the piezoelectric body has an input electrode and an output electrode provided on upper and lower surfaces by polishing and removing the second piezoelectric body. 5. A piezoelectric transformer manufacturing method using a green sheet laminating method, the green sheet to be the first piezoelectric body and a layer structure by laminating a green sheet comprising a second piezoelectric body and And said
The ceramic particle size of the green sheet serving as the second piezoelectric material is smaller than the ceramic particle size of the green sheet serving as the first piezoelectric material, and the green sheet serving as the first piezoelectric material is used as a firing jig. A method for manufacturing a piezoelectric body, comprising mounting and firing. 6. After firing the green sheet, the second sheet
6. The method according to claim 5, further comprising the step of polishing and removing the piezoelectric body.