JP3080033B2 - Multilayer piezoelectric transformer - 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 suitable for use in various high-voltage generating power supply circuits.
In particular, the present invention relates to the configuration of the internal electrodes of a multilayer piezoelectric transformer that is small, thin, and generates a high voltage, which requires small size and high reliability.

[0002]

2. Description of the Related Art Conventionally, 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, a winding type electromagnetic transformer is used as a transformer for generating a high voltage. Have been. This electromagnetic transformer has a structure in which a conductor is wound around a core made of a magnetic material, and in order to realize a high transformation ratio, it is necessary to increase the number of conductors wound around the core. For this reason, it has been very difficult to realize a small electromagnetic transformer.

On the other hand, a piezoelectric transformer using a piezoelectric effect has been proposed. FIG. 3 is a perspective view showing the structure of a conventional symmetric Rosen tertiary piezoelectric transformer.

Referring to FIG. 3, in the symmetric Rosen tertiary piezoelectric transformer, a rectangular piezoelectric plate 310 provided with electrodes on its surface, a portion indicated by 31 is a low impedance driving portion of the piezoelectric transformer. A planar electrode is provided on the upper and lower surfaces of the drive unit 31. FIG. 3 shows only the planar electrodes 311 and 313 on the upper surface side,
Planar electrodes are provided on the lower surface opposite to the planar electrodes 311 and 313, respectively, and this part (driving unit) is polarized in the thickness direction.

Similarly, a portion indicated by 32 is a high-impedance power generating portion, and a strip-shaped electrode 315,
In addition, a strip-shaped electrode is provided on the lower surface side facing this, and this portion (power generation unit) is polarized in the length direction of the piezoelectric plate.

When the piezoelectric transformer is driven by inputting an AC voltage between the external electric terminals 317 and 318 connected to the electrodes on the lower and upper surfaces of the drive unit 31, the external electric terminals 317 and the external electric terminals are driven. Voltage is output between terminals 319.

The external electric terminal 317 and the power generation unit 3
The voltage output between the external electric terminal 319 connected to the second electrode and the external electric terminal 319 is
It is determined by the voltage input in between and the step-up ratio of the piezoelectric transformer, and when trying to extract a high output voltage with a low input voltage, it is necessary to increase the step-up ratio of the piezoelectric transformer.

Incidentally, the step-up ratio of the piezoelectric transformer is determined by the thickness between the electrodes of the drive unit 31 and the length of the power generation unit 32. The step-up ratio becomes higher as the thickness is reduced and the length is increased.

However, in the case of the above-described piezoelectric transformer, since the piezoelectric plate is a single plate, there is naturally a limit in reducing the thickness between the electrodes of the drive unit 31 (practically, 0.5 m).
m), and the length is also limited in terms 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 conventional piezoelectric transformer for solving such a problem, for example, a laminated piezoelectric transformer as proposed in Japanese Patent Application Laid-Open No. Hei 6-224484 is known.
That is, JP-A-6-224484 discloses that in a piezoelectric ceramic transformer having a long plate structure, a driving unit in which a plurality of piezoelectric ceramic layers polarized in the thickness direction are alternately laminated with internal electrodes is provided at both ends of the piezoelectric transformer. A piezoelectric ceramic transistor having a structure in which a power generation unit polarized in the length direction is further disposed at a central portion including the center in the length direction and an output electric terminal is taken out from the center portion in the length direction has been proposed. . However, the above publication does not disclose the thickness and material of the internal electrodes and their influence on the piezoelectric transformer characteristics.

Known documents relating to the technology relating to the thickness of the laminated piezoelectric body and the internal electrode include, for example, Japanese Patent Application Laid-Open No.
460, JP-A-1-174199, JP-A-3-106082, JP-A-3-174772, JP-A-61-272983, and the like. The following is a brief description of these publications.

First, JP-A-64-460 discloses that
In the array type ultrasonic probe, in order to improve the separation between the piezoelectric body and the internal electrodes, the internal electrodes are meshed at a pitch of 10 μm or less, and the average thickness of the internal electrodes is 3 μm.
An array type ultrasonic probe described above has been proposed.

The above-mentioned Japanese Patent Application Laid-Open No. 1-174199 relates to a multilayer ultrasonic probe, in which when the internal electrode is too thin, the conductivity is deteriorated, and the internal electrode is separated from the piezoelectric body. To improve the problem,
16 ~ 2 piezoelectric ceramic powder for metal powder for internal electrode
A paste having a composition of 5 wt% is applied to a green sheet mainly composed of piezoelectric ceramics to a thickness of 10 to 15 μm, and at least one coating film of the paste is formed inside using the green sheet. A method of manufacturing a multilayer ultrasonic probe, in which an interposed laminate is created, the laminate is fired, the internal electrode layer is integrated between the piezoelectric ceramic layers, and the external electrode layer is formed, and then cut into an array. Proposed.

Further, Japanese Patent Laid-Open Publication No. Hei 3-106082 discloses an object for improving the problem that cracks are generated in the element due to shear stress generated between the piezoelectric body and the protective layer, and the insulating property is destroyed. The thickness of the internal electrode at the portion in contact with the piezoelectric body is set to 1/50 to 1/10 of the thickness of the piezoelectric body,
There has been proposed a multilayer piezoelectric actuator element in which the thickness of the internal electrode at the portion in contact with the protective layer is set to be 1/10 to 1/5 of the thickness of the piezoelectric body.

The above-mentioned Japanese Patent Application Laid-Open No. Hei 3-174772 aims to improve the problem that cracks are generated in the element due to shear stress generated between the piezoelectric body and the protective layer and the insulating property is destroyed. And a laminated piezoelectric actuator element in which the thickness of the internal electrode embedded between the piezoelectric bodies is set to 10 to 15 μm, and the thickness of the internal electrode in the laminated region outside the internal electrode in the central laminated region is increased. Has been proposed.

Japanese Patent Application Laid-Open No. 61-272984 discloses an electrostrictive element in which the thickness of an internal electrode is 5 μm as an embodiment.

[0018]

However, the above prior art has the following problems.

(1) As a first problem, in the conventional Rosen tertiary type piezoelectric transformer, a high output voltage is obtained with a low input voltage. It is necessary to reduce the thickness or the length of the power generation unit.However, since the piezoelectric plate is a single plate, there is a natural limit in reducing the thickness between the electrodes of the drive unit. This means that the length of the part is also limited in terms 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.

(2) As a second problem, a multilayer piezoelectric transformer is described in JP-A-6-224484 in order to improve the first problem.
No mention is made of the thickness and material of the internal electrodes and their influence on the piezoelectric transformer characteristics.

In order to increase the conversion efficiency of the piezoelectric transformer, it is necessary to optimize them.

(3) As a third problem, Japanese Patent Application Laid-Open No.
As described in Japanese Patent Application Laid-Open No. 4-460, when the internal electrodes are formed in a mesh shape, there is a problem in electrical conductivity as compared with the case where the internal electrodes are formed uniformly. In view of this, there is a problem that the conversion efficiency is reduced.

(4) As a fourth problem, as described in the above-mentioned JP-A-1-174199, JP-A-3-106082 and JP-A-3-174772, the thickness of the internal electrode is reduced. 10 to 15 μm, 4 to 2
When formed as thick as 0 μm, 20 to 40 μm, and 10 to 50 μm, from the viewpoint of the vibration of the piezoelectric transformer, the internal electrode is a heavy load for vibration. There is a problem that it is lowered.

(5) The above-mentioned JP-A-61-272988
In the publication, as an example, the thickness of the internal electrode is set to 5 μm.
Although described as an electrostrictive effect element, when viewed as an application to a piezoelectric transformer, the thickness of the internal electrode is relatively optimized from the relationship with the thickness of the piezoelectric body. It is not limited to one thickness.

Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to specify the thickness of an internal electrode so that when a piezoelectric transformer vibrates,
It is an object of the present invention to provide a multilayer piezoelectric transformer that prevents internal electrodes from becoming a heavy load and hinders vibration, and allows a sufficiently large conversion efficiency of the multilayer piezoelectric transformer to be obtained.

[0027]

In order to achieve the above object, a laminated piezoelectric transformer according to the present invention comprises: a driving unit in which a plurality of piezoelectric layers polarized in a thickness direction and internal electrodes are alternately laminated; A power generation unit provided to face the drive unit, wherein the thickness of the internal electrode is approximately 2 μm or more and approximately 10 μm or less, or the piezoelectric body layer About 3% or less of the thickness.

In the present invention, the material of the internal electrode is Ag
And Pd, and the powder of the piezoelectric body is contained in the material of the internal electrode.

In the present invention, the composition ratio of Ag / Pd of the material of the internal electrode is expressed by weight ratio (wt%) of Ag70.
~ 80 / Pd30 ~ 20, and the content of the piezoelectric powder is about 5 ~ 20wt%.

[0030]

Embodiments of the present invention will be described below. First, the principle and operation of the present invention will be described.

The piezoelectric transformer utilizes the vibration on the input side,
Power is extracted by the piezoelectric effect on the output side, and is basically a vibrator, and the state and magnitude of the vibration affect the amount of extracted power and the conversion efficiency. For this reason,
When a heavy load is applied to the vibrator, the vibration is hindered and the vibration level cannot be increased, and the power extraction amount and the conversion efficiency decrease. That is, in the case of a laminated piezoelectric transformer, if the thickness of the internal electrode is too large, it becomes a heavy load, hinders vibration, and lowers the conversion efficiency.

On the other hand, if the thickness of the internal electrodes is excessively reduced to improve this problem, sufficient electrical conduction cannot be obtained, which causes a problem in driving.

As described above, in the internal electrode used in the multilayer piezoelectric transformer according to the present invention, the thickness on the maximum side (upper limit) of the electrode is set to a level that does not hinder the vibration due to the weight load. The thickness on the minimum side (lower limit) of the electrode is optimized to a level that allows sufficient conduction.

Further, in order to improve the bonding strength between the piezoelectric body and the internal electrode and the electrical conductivity of the internal electrode, the internal electrode material to be used and the amount of the piezoelectric powder added thereto are optimized.

The present invention, in a preferred embodiment thereof, comprises a piezoelectric body (111 in FIG. 1) polarized in the thickness direction,
A drive unit (11 in FIG. 1) in which a plurality of internal electrodes (112 and 113 in FIG. 1) are alternately stacked, and a power generation unit (12 in FIG. 1) provided to face the drive unit are provided. In the laminated piezoelectric transformer, the thickness of the internal electrode is preferably about 2 μm or more on the lower limit side and 10 μm or less on the upper limit side or about 3% or less of the thickness of one piezoelectric body.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG. 1 is a perspective view showing the structure of a first embodiment of the present invention. Referring to FIG. 1, a portion indicated by reference numeral 11 is a low-impedance driving unit of a piezoelectric transformer, in which a plurality of piezoelectric bodies 111 and internal electrodes 112 and 113 are alternately laminated, and external electrodes formed on upper and lower surfaces are formed. Although the external electrodes 114 on the upper surface are shown in FIG. 1, the external electrodes are provided at corresponding positions on the lower surface. Reference numeral 116 denotes an external electrode for electrically connecting the internal electrodes 112 and 113 exposed on the side surfaces facing each other. Note that, in FIG.
An external electrode (not shown) is also provided on a side surface opposite to the side surface on which is provided. And between these electrodes (drive part) is polarized in the thickness direction.

A portion indicated by reference numeral 12 is a high-impedance power generation portion, and a band-shaped electrode 118 is provided. This portion is polarized in the length direction of the piezoelectric transformer.

The piezoelectric transformer of this embodiment has an external electric terminal 119 connected to an external electrode (not shown) provided on the lower surface.
When an AC voltage is input between the external electric terminal 120 and the external electric terminal 120 connected to the external electrode 114 and driven, the external electric terminal 119 is driven.
Then, a voltage is output between the external electric terminals 121 connected to the strip electrode.

Next, the manufacturing method of this embodiment will be described.

As the piezoelectric transformer, the piezoelectric transformer having the structure shown in FIG. 1 was manufactured by a green sheet method. Piezoelectric body 1
11 was Nepec 8 (manufactured by Tokin).

The internal electrodes 112 and 113 are made of a baked Ag / Pd paste (where the silver Ag / palladium Pd ratio is 70/30 by weight (wt%) and the piezoelectric powder 5
wt%) is adjusted so that the thickness after sintering is 2 to 10 μm, and is screen-printed on a green sheet of the piezoelectric body 111 in a predetermined pattern, and then laminated.
11 together with a temperature of 1200 ° C. and a keeping time of 2 hours.

Here, PZT-based piezoelectric ceramics and Ag / Pd are used as the material of the piezoelectric body and the internal electrode. However, any combination of a piezoelectric material having piezoelectricity and an electrode material which can be fired integrally therewith may be used. Needless to say, it works.

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.

Next, after firing, it is processed into dimensions of 42 mm in length, 5 mm in width, and 1 mm in thickness. And after printing at a predetermined position on the side, temperature 7
The external electrodes 114 and 116 and the strip electrode 118 were formed by baking at 00 ° C. for a keeping time of 15 minutes.

In the above embodiment, the power generation section 12 has been described as an example in which the internal electrodes are not laminated. However, the power generation section 12 in which the internal electrodes are laminated can be manufactured by the same process.

Next, using a polarization jig, a temperature of 300 to 3
Electric field is set to 0.5 to 0.7 kV / m in air at 50 ° C.
After applying m, the temperature is reduced to 100 ° C. or less in the applied state, and the applied electric field is cut off to polarize the power generation unit 11.

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

The resulting piezoelectric transformer is 100 k
FIG. 2 shows the results of evaluating the transformer characteristics by applying a voltage with Ω as a load.

From FIG. 2, the range of the thickness of the internal electrode is 2 to 2.
It can be seen that the conversion efficiency is reduced when the thickness is outside 10 μm. That is, when the thickness of the internal electrode is thinner than 2 μm, the electrical conductivity is deteriorated, and the conversion efficiency is rapidly reduced (75% at 1 μm).
The electrode became a heavy load, hindered the vibration, and reduced the conversion efficiency. Therefore, in order to realize higher conversion efficiency than before, it is important to specify the thickness of the internal electrode within the above range.

[Embodiment 2] The second embodiment of the present invention is the first embodiment.
The difference from the embodiment is that the amount of the piezoelectric powder added to the internal electrode material is changed. That is, in the second embodiment of the present invention, the Ag / Pd paste of the internal electrode was prepared by mixing the Ag / Pd ratio of 70/30 and the piezoelectric powder by 20 watts.
In this case, the thickness after sintering was adjusted to 2 to 10 μm and printing was performed.

The resulting piezoelectric transformer was 100 k
The results of the evaluation of the transformer characteristics by applying a voltage with Ω as a load (indicated by □) are shown in FIG. 2 together with the results of the first embodiment (indicated by 前 記).

As apparent from FIG. 2, the effect of the thickness of the electrode changes slightly depending on the amount of the piezoelectric substance to be added. This is considered to be due to the difference in electrical conductivity due to the added piezoelectric material. However, practically, a high efficiency (90% or more) not achieved by the conventional technology is realized, and there is no problem at all. .

The amount of the piezoelectric powder to be added is 5 wt%.
If the amount is less than the above, delamination occurs between the piezoelectric body and the internal electrode, and the conversion efficiency is reduced. If the amount is more than 20 wt%, the electrical conductivity is reduced and the conversion efficiency is reduced.

In the above, the ratio of Ag / Pd is set to 70/30
Has been described, but this ratio is set to 80/20.
The same result was obtained even when it was changed in the range up to.

[0056]

As described above, according to the present invention, in the multilayer piezoelectric transformer, the thickness of the internal electrode is specified (2).
μm or more and 10 μm or less, or 3
% Or less) so that the vibration of the piezoelectric transformer is not hindered, there is an effect that the conversion efficiency of the multilayer piezoelectric transformer can be sufficiently increased.

[Brief description of the drawings]

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

FIG. 2 is a graph showing a measurement result of the example of the present invention.

FIG. 3 is a perspective view showing a configuration of a conventional single-plate type piezoelectric transformer.

[Explanation of symbols]

11, 31 Drive unit 12, 32 Power generation unit 111 Piezoelectric body 310 Piezoelectric plate 112, 113 Internal electrode 114 External electrode 116 External electrode (for connecting internal electrode) 118 Strip electrode 311 313 Planar electrode 315 Strip electrode 119, 120, 121, 317, 318, 319 External electric terminals

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 41/107 H01L 41/22

Claims (5)

(57) [Claims] 1. A multi-layer piezoelectric device comprising: a drive section in which a plurality of piezoelectric bodies and internal electrodes polarized in a thickness direction are alternately stacked; and a power generation section provided to face the drive section. In the transformer, the thickness of the internal electrode is approximately 2 μm or more and approximately 10 μm or less, or approximately 3% or less of the thickness of the piezoelectric layer. . 2. The multilayer piezoelectric transformer according to claim 1, wherein the material of the internal electrode includes Ag and Pd, and the material of the internal electrode includes the powder of the piezoelectric body. Piezo transformer. 3. The multilayer piezoelectric transformer according to claim 2, wherein a composition of Ag / Pd of the material of the internal electrode is expressed by a weight ratio of A / Pd.
g70-80 / Pd30-20, wherein the content of the powder of the piezoelectric body is approximately 5-20 wt%. 4. A multi-layer piezoelectric device comprising: a driving unit in which a plurality of piezoelectric bodies and internal electrodes polarized in the thickness direction are alternately stacked; and a power generation unit provided to face the driving unit. In the transformer, the thickness of the internal electrode is approximately 2 μm or more and approximately 10 μm.
m or less. 5. A multilayer piezoelectric device comprising: a driving section in which a plurality of piezoelectric bodies and internal electrodes polarized in the thickness direction are alternately laminated; and a power generation section provided to face the driving section. In the transformer, the thickness of the internal electrode is approximately 2 μm or more, and approximately 3% or less of the thickness of the piezoelectric layer.