JP2907153B2 - Piezoelectric transformer and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer used in various power supply circuits for generating a high voltage, and more particularly to a small, thin, and high-voltage piezoelectric transformer requiring high conversion efficiency and high reliability. It is related to the configuration of

[0001]

2. Description of the Related Art Conventionally, a winding type electromagnetic transformer has been used as a transformer for generating a high voltage in a power supply circuit in a device requiring a high voltage such as a deflection device of a television or a charging device of a copying machine. However, it is very difficult to realize a small-sized electromagnetic transformer because it is necessary to increase the number of conductors wound around a magnetic core in order to realize a high transformation ratio. In particular, it is inappropriate to use an electromagnetic transformer because a cold cathode tube inverter of a backlight for a display mounted on a recent portable information device is strictly required to be small and thin.

On the other hand, a piezoelectric transformer using a piezoelectric effect has been proposed. As an example of this, the structure of a Rosen-type piezoelectric transformer is shown in FIG. In this Rosen-type piezoelectric transformer, a rectangular piezoelectric plate 2 provided with electrodes on its surface is provided.
In FIG. 10, a portion indicated by 21 is a low impedance driving portion of the piezoelectric transformer, and a planar electrode 21 is provided on the upper surface thereof.
1 and a planar electrode provided on the lower surface opposite to this, and this portion is polarized in the thickness direction as shown by an arrow 23.

[0003] Similarly, a portion indicated by reference numeral 22 is a high-impedance power generation portion, and an end face electrode 213 is provided. This portion is polarized in the length direction as indicated by an arrow 24. This piezoelectric transformer has external electric terminals 214 and 2
When an AC voltage having a resonance frequency of 1/2 or 1 wavelength resonance is input between the external electric terminals 215 and
And 216 output a voltage.

The voltage output between the external electric terminals 215 and 216 is determined by the vibration level of the piezoelectric transformer and the step-up ratio of the piezoelectric transformer.
It is necessary to increase the voltage input between the external electric terminals 214 and 215 to increase the vibration level of the piezoelectric transformer or to increase the step-up ratio of the piezoelectric transformer itself.

[0005] When the vibration level of the piezoelectric transformer is increased by increasing the input voltage, there is a problem that the piezoelectric transformer is broken by a stress accompanying resonance.
To solve this problem, there is one disclosed in JP-A-6-112542. This is to increase the mechanical strength of ceramics by using fine ceramic powders for the piezoelectric material and reducing the crystal particle size of the sintered body to 1 μm or less to produce dense ceramics with few voids. Thus, even if the vibration level is increased by increasing the input voltage, the piezoelectric transformer is hardly broken.

However, in the method of increasing the input voltage, increasing the vibration level, and increasing the output voltage by using the above-described piezoelectric transformer having a single-plate structure, the mechanical strength of the piezoelectric body must be increased. However, there is a limit to the output voltage that can be obtained. Incidentally, even when the particle diameter of the crystal grains of the piezoelectric material is reduced to 1 μm or less as in the above-mentioned conventional example, the mechanical strength is improved about twice, and the input voltage is reduced under a practical target load (100 kΩ). At 30Vrms, output voltage is at most 500
About Vrms.

On the other hand, as a method of increasing the output voltage, it is conceivable to increase the step-up ratio of the piezoelectric transformer. The step-up ratio of the piezoelectric transformer is determined by the thickness between the electrodes of the drive unit and the length of the power generation unit. , The longer, the higher the boost ratio.

However, when the piezoelectric plate is a single plate as in the above-described piezoelectric transformer, there is naturally a limit in strength (in practice, 0.5 mm) to reduce the thickness between the electrodes of the driving section.
The length is also limited for the purpose of miniaturization.
Further, when the thickness between the electrodes is reduced, there is a problem that the conversion efficiency of the piezoelectric transformer is reduced.

As a method for improving such a problem, T
OKIN Technical Review, NO.
22, p67-p74 (1996) (hereinafter referred to as Document 1) using a laminated piezoelectric transformer.

As an example of a laminated piezoelectric transformer, FIG. 5 shows an electrode pattern of the Rosen type piezoelectric transformer in which a piezoelectric body and internal electrodes are laminated.

In FIG. 5, a portion indicated by 31 is a low impedance driving portion of a piezoelectric transformer, in which a plurality of piezoelectric bodies 311 and internal electrodes 312 are alternately laminated, and an outer electrode 313 is provided on the outermost layer. An external extraction electrode is provided on the lower surface facing the electrode, an internal electrode connection electrode 315 is provided on the side surface, and an internal electrode connection electrode is provided on the side surface facing the external electrode. Each layer is polarized in the thickness direction.

A portion indicated by reference numeral 32 is a high-impedance power generation portion, provided with an end face electrode 317, and this portion is polarized in the length direction similarly to the single plate type. Then, similarly to the single-plate type piezoelectric transformer, the external electric terminals 31
When an AC voltage having a resonance frequency of ま た は or 1 wavelength resonance is input between 8 and 319, resonance occurs in the length direction, and a voltage is output between the external electric terminals 319 and 320.

In a laminated piezoelectric transformer, in principle, the step-up ratio increases in proportion to the number of layers. For example, in the case of a five-layer stack, the step-up ratio is about 5 times that of a single-plate type piezoelectric transformer having the same element thickness.
Double. By the way, when compared with the single-plate type piezoelectric transformer, an output voltage of 500 Vrms is obtained by 30 Vrms.
The input voltage of 6 Vrms is required for the multi-layer piezoelectric transformer instead of the input voltage of s.

As a method of manufacturing the laminated piezoelectric transformer, a piezoelectric green sheet on which a conductor is formed is laminated and then fired at 1100 ° C. Also, a lead-based oxide ceramic (PZT-based) is used as the piezoelectric body, and a silver-palladium alloy (hereinafter referred to as Ag / Pd) electrode is used as the internal electrode material.

[0015]

In the manufacturing method of the laminated piezoelectric transformer, the lead-based oxide ceramic (PZT-based) used for the piezoelectric transformer is made of crystal particles under the influence of the Ag / Pd electrode used for the internal electrode. It is known that the diameter increases.

Reference 1 describes that the crystal grain size of the sintered body near the internal electrode is about 5 μm, and the crystal grain size of the sintered body away from the internal electrode is 3 μm.

It has been found that when the crystal grain size is locally enlarged in the piezoelectric transformer, the transformer characteristics such as the mechanical quality factor Qm and the conversion efficiency are deteriorated due to the influence of vibration propagation and the like.

For example, when examining the conversion efficiency of the above-described conventional piezoelectric transformer, the multilayer piezoelectric transformer in which the crystal diameter of the driving unit on which the internal electrodes are laminated is 5 μm and the particle diameter of the power generation unit is 3 μm is shown. Was 90%. In addition, the particle size of the crystal particles of the driving unit is 5.2 to 7.2 μm,
When the particle diameter of the power generation unit was in the range of 4.0 to 5.0 μm, the conversion efficiency was even lower at approximately 85%.

When ceramic powder having the same fineness as that of a single-plate type piezoelectric transformer is applied to a laminated piezoelectric transformer in order to suppress the enlargement of the particle diameter of the crystal particles, separation between the laminated layers (due to the packing effect) occurs. There is also the problem of doing it.

Therefore, the present invention provides a multilayer piezoelectric transformer which suppresses the enlargement of the particle size of crystal grains of the piezoelectric ceramics, specifies the range of the particle size, and significantly improves the characteristics of the piezoelectric transformer. An object of the present invention is to provide a small-sized and high-performance laminated piezoelectric transformer that has not been provided in a transformer.

[0021]

According to the present invention, there is provided a piezoelectric transformer element comprising: a drive section in which a plurality of piezoelectric layers polarized in a thickness direction and internal electrodes are alternately laminated; and a piezoelectric body polarized in a length direction. Wherein the piezoelectric body is made of a lead-based oxide ceramic, the internal electrode is made of a silver-based conductor, and the crystal size of the piezoelectric body of the driving section has a particle size of 2.5. ４4.0 μm, and the particle size of the crystal grains of the piezoelectric body of the power generation unit is 2.0 to 3.5 μm.
In the manufacture thereof, the piezoelectric transformer is fired at a temperature of 1,080 to 1,100 ° C.

When a lead-based oxide ceramic is used as the piezoelectric body and an Ag / Pd electrode is used as the internal electrode, the crystal size of the piezoelectric body is in a state of being enlarged, and the transformer characteristic is affected by the influence of vibration propagation. In this case, Qm and conversion efficiency are low. In view of this, the multilayer piezoelectric transformer of the present invention considers the influence of silver on the sinterability of lead-based oxide ceramics, optimizes the firing conditions, suppresses the enlargement of the crystal particle diameter, and reduces the transformer characteristics. Is significantly improved.

[0023]

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

FIG. 1 is a perspective view showing a first embodiment of the present invention.

In FIG. 1, a portion indicated by reference numeral 11 is a low impedance driving portion of the piezoelectric transformer, in which a plurality of piezoelectric bodies 111 and internal electrodes 112 are alternately laminated, and an external electrode 113 formed on the upper surface is opposed to the external electrode 113. Has an external electrode on the lower surface. In addition, an internal electrode connecting electrode 115 for electrically connecting the internal electrode 112 exposed on the side surface is provided on every other layer, and an internal electrode connecting electrode is provided on the opposite side surface facing the internal electrode 112. The driving section is polarized in the thickness direction.

A portion indicated by reference numeral 12 is a high-impedance power generating portion, and is provided with an end face electrode 117. This portion is polarized in the length direction of the piezoelectric transformer.

When the piezoelectric transformer is driven by inputting an AC voltage having a resonance frequency of ま た は or one wavelength resonance between the external electric terminals 118 and 119, the piezoelectric transformer is driven.
A voltage is output during 20.

In the multilayer piezoelectric transformer element according to the present invention, the crystal size of the piezoelectric body of the driving unit is 2.5 to 4.0 μm, and the particle size of the piezoelectric body of the power generation unit is 2.0 to 4.0 μm. 3.5μ
m. Further, such a range of the particle size is such that the peak temperature of the firing in the production is 10 ° C.
It is obtained in the range of 80 to 1100 ° C.

FIG. 2 is a graph showing the range of the particle size of the driving portion and the power generation portion of the piezoelectric body, and the properties of the piezoelectric body or the characteristics of the laminated piezoelectric transformer in which the piezoelectric body has the particle size in the range. The basis for specifying the range of the particle size of the invention is shown. FIG.
The B region shown in the above is a range in which the particle diameter of the power generation unit is larger than the particle diameter of the drive unit. Since the particle size of the power generation unit cannot be larger than the particle size of the drive unit having an internal electrode of Ag / Pd or the like, the region B is a range in which formation is not possible. On the other hand, C
The region is a range in which the particle shape of the drive unit is much larger than the particle size of the power generation unit, and is a range in which formation cannot be performed stably even if the conditions are changed. Further, in the range of the region A, the particle size of the power generation unit is less than 2 μm, the piezoelectric body is hardly polarized, and the piezoelectric ceramic cracks or cracks when the electric field for the polarization treatment is increased. Therefore, the polarization is in an inappropriate range. In the area E, the particle size of the power generation unit is 2 μm or less, but the particle size of the drive unit is 2 μm or less.
Since it is less than 5 μm, the conversion efficiency of the piezoelectric transformer is 95%.
%. The area D is an area in which the particles of the driving section are enlarged beyond 4 μm, and are areas where characteristics such as the conversion efficiency of the piezoelectric transformer are low. Also, F
The region is a region where the particle size of the driving unit is 4 μm or less, but the conversion efficiency of the piezoelectric transformer is less than 95% because the particle size of the power generation unit exceeds 3.5 μm. In the G region in the figure, as described above, the particle size of the driving unit is 5.2 to 7.0.
2 μm, the particle size of the power generation unit is in the range of 4 to 5 μm, and the exchange efficiency is at most 85% in the case of the multilayer piezoelectric transformer. H is an example described in Document 1 and indicates that the exchange efficiency is 90%.

On the other hand, according to the present invention, when the particle diameters of the driving section and the power generation section are in the range of 2.5 to 4.0 μm and 2.0 to 3.5 μm, the conversion efficiency is 95% or more. It is clear from FIG. 2 that a type piezoelectric transformer is obtained. Further, the value of Qm is as excellent as 1500 or more. Piezoelectric transformers are strictly required to be small, thin, and have high conversion efficiency. If the performance is inferior to this, the practical value of the piezoelectric transformer is lost.

Next, a manufacturing method according to an embodiment of the present invention will be specifically described.

The piezoelectric transformer of the present invention was manufactured by a green sheet method using the piezoelectric transformer having the structure shown in FIG.
The material of the piezoelectric body 111 was Nepec 8 (manufactured by Tokin Co., Ltd., specific surface area of powder: 1 m 2 / g).

The internal electrode 112 is made of a firing type A
The g / Pd paste is formed on a green sheet of the piezoelectric body 111, and is screen-printed in a pattern in which the electrodes on the side are removed in a strip shape, and then laminated. , And a total firing time of 24 hours.

As for the configuration of the lamination, five layers of piezoelectric bodies and four layers of internal electrodes were provided on the input side, and the thickness of each piezoelectric body 111 was 200 μm, and the total thickness was 1 mm.

Then, after firing, it is processed into dimensions of 36 mm in length, 5 mm in width, and 1 mm in thickness, and a firing type Ag / Pd paste is printed on the upper and lower surfaces of the drive unit 11 and the end surface of the power generation unit 12, and then heated to a temperature of 700 ° C. By sintering under the condition of a maintenance time of 15 minutes, the internal electrode connecting electrode 115 and the internal electrode connecting electrode and the end face electrode 117 on the side surface facing the internal electrode connecting electrode 115 were formed.

Then, using a polarization jig, a temperature of 300 to
An electric field of 0.5 to 0.7 kV /
mm, the temperature is reduced to 100 ° C. or less in the applied state, and then the applied electric field is cut off to generate the power generation unit 11.
Was polarized.

Subsequently, an electric field of 2 to 3 kV / mm was applied in silicone oil at a temperature of 100 to 200 ° C. to polarize the driving section 12.

The resulting piezoelectric transformer is 100 k
When a transformer was evaluated by applying a voltage with Ω as a load, the Qm was 1800 and the conversion efficiency was 95%.
Compared to the conventional multilayer piezoelectric transformer having a Qm of 900 and a conversion efficiency of 85%, the results showed that the characteristics were significantly improved.

Further, the particle size of crystal grains of the piezoelectric body portion of the obtained multilayer piezoelectric transformer was measured.
In the driving section, the average particle diameter is 3.4 μm,
In the power generation section, the average particle diameter was 2.7 μm.

Incidentally, a peak temperature of 1080 ° C. and a maintenance time of 2
The same result was obtained under the firing conditions of time.

The laminate obtained by integrally firing the laminate manufactured in the same manner under the conditions of a heating rate of 100 ° C./hour, a peak temperature of 1120 ° C., a maintenance time of 2 hours, and a total firing time of 24 hours. For the piezoelectric part of the piezoelectric transformer, the particle diameter of the crystal particles was measured.
The average particle size is 5.2 μm, and in the power generation section,
The average particle size was 4 μm. When the transformer characteristics were evaluated, the Qm and the conversion efficiency were low as in the conventional example (Qm: 1100, conversion efficiency: 86).
%). FIG. 2 is plotted as a poor example.

On the other hand, the laminated piezoelectric transformer obtained by integrally firing under the conditions of a heating rate of 100 ° C./hour, a peak temperature of 1050 ° C., a maintenance time of 2 hours, and a total firing time of 24 hours has an insufficient firing state. It did not sufficiently function as a transformer and was not worthy of evaluation.

Next, another embodiment will be described. The difference from the previous embodiment is that a firing type (carrier type) electrode material is used as the external electrode and the polarization conditions are reviewed in accordance with this, so only this point will be described.

First, as a material for the external electrode, a curing type Ag paste was printed at a predetermined position in the same manner as in the previous embodiment, and then cured at a temperature of 200 ° C. for a maintenance time of 15 minutes.

Next, using a polarization jig, a temperature of 100 to 20
In silicone oil at 0 ° C., an electric field of 1.5 to 2
By applying kV / mm, the power generation unit 11 was polarized.

Subsequently, an electric field of 2 to 3 kV / mm was applied in silicone oil at a temperature of 100 to 200 ° C. to polarize the driving section 12.

The resulting piezoelectric transformer is 100 k
When the transformer characteristics were evaluated by applying a voltage with Ω as a load, the values of Qm and the conversion efficiency were almost the same as those of the first embodiment. Further, in this embodiment, there is a merit that the cost can be reduced in terms of the manufacturing process (especially, external electrode formation and polarization process) and the material used for the external electrode (compared to the cost of 80 yen / piece in the first embodiment, 60
Yen / piece).

In the above-described embodiment, the piezoelectric transformer vibrating at the resonance frequency of 1/2 wavelength or 1 wavelength resonance has been described, but the piezoelectric transformer having the configuration vibrating at the resonance frequency of 3/2 wavelength resonance has no effect. Has not changed. For example, FIG. 3 shows a structure of a third-order Rosen-type laminated piezoelectric transformer of a type that vibrates at a resonance frequency of 3/2 wavelength resonance. PZ having an internal electrode 412 such as Ag / Pd
This is an example in which a T-based ceramic sheet 421 is integrally sintered and external electrodes 413 and external electric terminals 418, 419, 420 are attached. Also in this example, the particle diameters of the crystal particles of the piezoelectric driving units 41 and 43 are set to 2.5 to 4.0 μm,
2 has a particle diameter of 2.0 to 3.5 μm.

[0048]

As described above, the present invention relates to a laminated piezoelectric transformer which uses a lead-based oxide ceramic as a piezoelectric material and a silver-based conductor as an internal electrode. It is fired at a temperature, and the particle size of the crystal grains of the piezoelectric body in the drive unit where the internal electrodes are laminated is 2.5 to 4.0 μm, and the crystal grain size of the piezoelectric body in the power generation unit is 2.0 to 3. By adjusting the thickness to 5 μm, there is an effect that the transformer characteristics of the multilayer piezoelectric transformer, such as Qm and conversion efficiency, are significantly improved.

Further, since the performance of the transformer is remarkably improved by the present invention, it is possible to provide a small, thin, high-voltage and high-efficiency piezoelectric transformer. For example, it is very useful when used for a cold cathode tube inverter of a display backlight mounted on a portable information device represented by a notebook personal computer. This is because portable information devices are strictly required to be small and thin.

[Brief description of the drawings]

FIG. 1 is a perspective view of a piezoelectric transformer showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating ranges of particle diameters of a driving unit and a power generation unit of a piezoelectric body, and properties of the piezoelectric body or characteristics of a laminated piezoelectric transformer.

FIG. 3 is a diagram showing the structure of a tertiary Rosen-type laminated piezoelectric ceramic transformer of the present invention.

FIG. 4 is a perspective view showing a conventional single-plate type piezoelectric transformer.

FIG. 5 is a perspective view showing a conventional laminated piezoelectric transformer.

[Explanation of symbols]

11, 21, 31, 41, 43 Drive unit 12, 22, 32, 42 Power generation unit 111, 311 Piezoelectric body 210 Piezoelectric plate 112, 312, 412 Internal electrode 113, 313, 413, 414 External electrode 115, 315 Internal electrode connection Electrodes 117, 213, 317 End face electrodes 211 Planar electrodes 118, 119, 120, 214, 215, 216, 3
18, 319, 320, 418, 419, 420 External electric terminal 23 Arrow indicating polarization in thickness direction 24 Arrow indicating polarization in length direction 421 Ceramic sheet

Claims (4)

(57) [Claims] 1. A piezoelectric transformer, comprising: a driving unit in which a plurality of piezoelectric bodies and internal electrodes polarized in a thickness direction are alternately stacked; and a power generation unit including a piezoelectric body polarized in a length direction. The particle size of the piezoelectric crystal grains of the driving unit is 2.5
A piezoelectric transformer, wherein the diameter of the crystal grains of the piezoelectric body of the power generation unit is smaller than the diameter of the crystal grains of the piezoelectric body of the drive unit. 2. The power generation unit according to claim 1, wherein the crystal particles of the piezoelectric body have a particle size of 2.0 to 3.5 μm.
The described piezoelectric transformer. 3. The piezoelectric transformer according to claim 1, wherein the piezoelectric body is made of a lead-based oxide ceramic, and the internal electrode is made of a silver-based conductor. 4. A method of manufacturing a piezoelectric transformer having a power generation unit and a driving unit having a laminated structure, wherein a plurality of layers of lead-based oxide ceramics and silver-based conductor internal electrodes are alternately laminated as the driving unit. Firing at a temperature in the range of 1 to 1100 ° C to reduce the particle size of the crystal particles of the driving section to 2.5 to 4.0 μm.
m, a method for manufacturing a piezoelectric transformer.