JPH0992898A - Piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric transformer which has such a structure that no microcrack defect may appear at the time of polarization and the device may not break even if it is used for a long time and a high reliability can be achieved. SOLUTION: This is a piezoelectric transformer using a resonance mode in the longitudinal direction of a piezoelectric rectangular board 11 made of piezoelectric ceramic. Such a piezoelectric transformer has surface electrodes 12 and 13 which are so located as to cover nearly half the area in the longitudinal direction of the piezoelectric rectangular board 11 and which face each other in the thickness direction and a plurality of belt-like internal electrodes 14 which are located at the center of the remaining half area in the longitudinal direction of the piezoelectric rectangular board 11 and which are also located at one-fourth position in the longitudinal direction of the piezoelectric rectangular board 11 from one end of the board 11 and which are so formed as to cross at right angles with the longitudinal direction of the piezoelectric rectangular board 11. The belt-like internal electrodes 14 are connected to belt-like external electrodes 15 and 16 on side faces of the piezoelectric rectangular board 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer using piezoelectric ceramics, and in particular, a piezoelectric rectangular plate made of piezoelectric ceramics is provided with electrodes for polarization and input / output, and The present invention relates to a piezoelectric transformer that utilizes resonance in the length direction.

[0002]

2. Description of the Related Art Conventionally, a high voltage power supply of about 1 kV-several watts has been used for a static electricity generator or for lighting a backlight of a liquid crystal display without requiring a large current value. Currently, electromagnetic transformers are used for boosting these power supplies, but due to demands such as reduction of generated electromagnetic noise, low power consumption, and small and low profile of equipment,
The practical application of the piezoelectric transformer is being studied.

FIG. 3 is a schematic perspective view of the structure of a piezoelectric transformer 30 using a conventional λ-mode piezoelectric vibrator. In FIG. 3, on the surface of a rectangular plate 31 (hereinafter referred to as a piezoelectric rectangular plate) made of piezoelectric ceramics, electrodes 32 and 3 facing each other in the thickness direction are formed in approximately half the length direction.
3 are formed respectively. Further, the strip-shaped surface electrodes 34 and 35 extending in the direction orthogonal to the length direction are provided at approximately half positions in the length direction on the side opposite to the portion where the pair of surface electrodes 32 and 33 of the piezoelectric rectangular plate 31 are formed. Has been formed. In the piezoelectric rectangular plate 31, the surface electrodes 32 and 33 are polarized in the thickness direction as shown by an arrow 36, and the part between the strip-shaped surface electrodes 34 and 35 is a piezoelectric rectangular plate as shown by an arrow 37. 31 is polarized in the longitudinal direction.

Further, as the piezoelectric transformer 30, the piezoelectric rectangular plate is supported at a vibration nodal point which has little influence on the vibration of the ceramic rectangular plate.
And it is necessary to take out the input / output electrodes at the nodes, 41, 4
Reference numerals 1'indicate nodes of λ-mode vibration, respectively.

FIG. 4 is an explanatory view of the operating principle of a λ-mode resonance drive piezoelectric transformer using the piezoelectric vibrator of FIG. 3, FIG. 4 (a) is a sectional view of a piezoelectric rectangular plate, and FIG. 4 (b) is FIG. 4C shows a strain distribution when the piezoelectric rectangular plate vibrates in the one-wavelength resonance mode of longitudinal vibration, and FIG. 4C shows a strain distribution at that time. In FIG. 4A, when the surface electrode 33 is used as a ground terminal and a voltage having a frequency equal to the resonance frequency of the one-wavelength resonance mode in the length direction of the piezoelectric rectangular plate 31 is applied to the surface electrode 32, the piezoelectric rectangular plate 4) Vibrate as shown in (b) and (c). At this time, a voltage is generated between the surface electrode 33 and the strip-shaped surface electrodes 34 and 35 by the piezoelectric effect. Here, the input voltage applied to the surface electrode 32 and the output voltage generated between the strip-shaped surface electrodes 34 and 35 will be described.
It is sufficiently smaller than the distance between the strip surface electrodes 34 and 35,
Since the area of the surface electrodes 32 and 33 is sufficiently larger than the area between the strip-shaped surface electrodes 34 and 35, the electrostatic capacitance on the input side is sufficiently larger than the electrostatic capacitance on the output side. Therefore, when a low voltage is applied to the input side to vibrate the oscillator, the ratio of the input side electrode spacing to the output side and the spacing between the input side electrode and the output side electrode, A large proportional voltage is generated.

[0006]

In the piezoelectric transformer described with reference to FIG. 3, the rectangular plate thickness direction polarization between the input side surface electrodes 32 and 33 can be uniformly polarized. In addition, the polarization on the output side can be uniform in the length direction in the ceramic part without surface electrodes. However, the surface electrodes 32, 33
Piezoelectric rectangular plate 31 central end and strip surface electrodes 34, 35
In the vicinity of, since the electrode directly under the electrode is equipotential and the electric field direction is orthogonal to the electrode surface, the polarization direction is also orthogonal to the electrode surface, and as a result, the central portions of the rectangular plates of the surface electrodes 32 and 33 are In the vicinity of the strip-shaped surface electrodes 34, 35, distortion due to polarization is concentrated. In the piezoelectric rectangular plate 31, defects such as microcracks are likely to occur at locations where strain due to this polarization is concentrated.

Further, as described with reference to FIG. 4 (c), the strip-shaped surface electrodes 34, 35 correspond to the nodes 41, 41 of vibration, and correspond to the site where the strain at the time of vibration becomes the maximum, and the micro-electrodes generated by polarization. The crack grows due to the concentration of vibration strain when the piezoelectric transformer is driven, and the crack grows further when used for a long time.
There is a defect that 1 leads to destruction.

[0008] Therefore, the technical problem of the present invention is to provide a piezoelectric transformer having a structure in which defects of microcracks do not occur during polarization, they do not break even when used for a long time, and high reliability is obtained. Especially.

[0009]

[Means for Solving the Problems] As described above, the polarization concentration at the output electrode portion of the piezoelectric transformer is caused when the electric line of force in the length direction of the output side piezoelectric ceramic is polarized at the shortest distance between the surface electrodes. This is due to the distribution orthogonal to the electrodes. Furthermore, the fact that the polarization distortion concentration part and the vibration distortion maximum part when the piezoelectric transformer is driven coincide with each other is the cause of the decrease in reliability that leads to damage when the piezoelectric transformer is driven for a long time. . Therefore, the inventors of the present invention can prevent the occurrence of microcracks by dispersing the concentration of strain at the time of polarization at the site of the maximum strain of vibration at the time of driving the piezoelectric transformer. The present invention has been found to be effective for prevention, and has led to the present invention.

According to the present invention, in a piezoelectric transformer utilizing a resonance mode in the length direction of a piezoelectric rectangular plate made of a piezoelectric ceramic, the piezoelectric transformer is provided at approximately half the length of the piezoelectric rectangular plate and has a thickness. A pair of surface electrodes facing each other in the direction of the piezoelectric rectangular plate, and the piezoelectric rectangular plate is provided at a position approximately one-quarter of the lengthwise half of the piezoelectric rectangular plate in the longitudinal direction. A plurality of strip-shaped internal electrodes formed in a direction intersecting with the length direction of the plate, and strip-shaped external electrodes provided on the side surface of the piezoelectric rectangular plate and connected to the strip-shaped internal electrodes. A piezoelectric transformer that operates is obtained.

Further, according to the present invention, in the piezoelectric transformer, the front surface electrode is connected to a strip-shaped side surface electrode provided on a side surface of the piezoelectric rectangular plate at a substantially middle position in the longitudinal direction, Further, the external electrode further extends on the surface of the piezoelectric rectangular plate so as to face the internal electrode, thereby obtaining a piezoelectric transformer.

[0012]

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

First, a first embodiment of the present invention will be described.

FIG. 1 is a perspective view of a piezoelectric transformer according to a first embodiment of the present invention. As shown in FIG. 1 (a),
A piezoelectric transformer 10 using a λ-mode piezoelectric vibrator includes front surface electrodes 12 and 13 facing each other in about half of a front surface and a back surface of a rectangular plate (hereinafter referred to as a piezoelectric rectangular plate) 11 made of piezoelectric ceramic. Layers have been formed. In addition, at the central portion of the remaining half of the rectangular plate 11 in the length direction, that is, at a position of ¼ of the length of the piezoelectric rectangular plate 11, the piezoelectric rectangular plate 11 is provided inside the piezoelectric rectangular plate 11. A plurality of strip-shaped internal electrodes 14 (four rows in the drawing) that are long in the width direction are formed in parallel with each other, facing each other in the thickness direction of the piezoelectric rectangular plate 11. The strip-shaped internal electrodes 14 in a plurality of rows extend to both sides of the piezoelectric rectangular plate 11, and both ends thereof are connected to the side surfaces of the piezoelectric rectangular plate 11 and the external electrodes 15 and 16 formed long in the thickness direction, respectively. .

Here, with the surface electrodes 12, 13 as one end,
The strip-shaped internal electrode 14 is connected to the other end, that is, the pair of external electrodes 1
When a high DC voltage is applied between one end and the other end with 5, 16 as the other end and one end as a positive electrode, a line of electric force is formed and polarized as shown by a broken line 17 in FIG. In the polarized state, one surface electrode 1 is placed between the surface electrodes 12 and 13.
When the primary side AC voltage V1 is applied with 3 as the earth to resonate the piezoelectric rectangular plate 11, a secondary side high AC voltage V2 is generated between the surface electrode 13 and the external electrodes 15 and 16. In addition, reference numerals 41 and 41 ′ indicate contacts for λ-mode vibration, and are located at λ / 4 from both ends of the piezoelectric rectangular plate 11.

The piezoelectric transformer 10 shown in FIGS. 1A and 1B is manufactured as follows. First, an output section strip-shaped electrode pattern is printed with a silver-palladium electrode paste on a PZT-based piezoelectric ceramics green sheet having a thickness of 230 μm, five layers of the printed sheets are laminated, and a ceramic green sheet having no electrode pattern is formed thereon. The layers were laminated, the laminate was thermocompression bonded, and sintered in air at 1150 ° C. Next, a silver paste is used to form surface electrodes facing each other in the thickness direction at approximately half the length of the rectangular plate that does not include the internal strip electrodes. 40m long by forming a band-shaped external electrode to be connected
A piezoelectric transformer with m, width of 10 mm, and thickness of 1 mm in the longitudinal direction single wavelength resonance mode was prototyped. Since the nodes of the one-wavelength resonance mode are located 10 mm from the end faces of the piezoelectric ceramic rectangular plate in the lengthwise direction, they support the external electrodes and surface electrode parts in the vicinity, and connect the electrodes with lead wires. Part and The polarization of a piezoelectric ceramic has a temperature of 150
It was carried out at a temperature of 1.2 ° C. and an electric field strength of 1.2 kV / mm. The ceramic crystal grain size, mechanical and electrical performance of the piezoelectric transformer of the first embodiment are shown in Table 1 below in comparison with the conventional structure.

Next, a second embodiment of the present invention will be described.

FIG. 2 shows a λ according to the second embodiment of the present invention.
It is a perspective view showing a piezoelectric transformer using a mode piezoelectric vibrator. As shown in FIG. 2A, the piezoelectric transformer 20 includes a rectangular plate 21 made of piezoelectric ceramic and a surface electrode 22, 23.
2 and the strip-shaped internal electrode 26 are formed, the structure is similar to that of the piezoelectric transformer 10 according to the first embodiment. However, the piezoelectric transformer 20 according to the second embodiment is formed such that part of the layers of the surface electrodes 22 and 23 extend to the side surface of the piezoelectric rectangular plate 21 and the side surface electrodes 24 and 25 face each other. And the external electrodes 27 contacting the strip-shaped internal electrodes 26 are formed in a ring shape extending on the front and back sides so as to face the strip-shaped internal electrodes 26, respectively.

Here, the pair of side surface electrodes 24, 25 connected to the surface electrodes 12, 13 are used as one end, and the strip-shaped internal electrode 2
When the external electrode 27 connected to 6 is the other end and one end is the positive electrode and a high DC voltage is applied between the one end and the other end, an electric force line is formed as shown by a broken line 28 in FIG. 2B. And be polarized.

In the polarized state, when one side electrode 24 is grounded and the primary side AC voltage V1 is applied between the side electrodes 24 and 25 to cause the piezoelectric rectangular plate 21 to resonate, the side electrodes 24 and A high AC voltage V2 on the secondary side is generated between the external electrode 27 and the external electrode 27. Incidentally, reference numerals 41 and 41 'indicate nodes of vibration of the λ mode, which are located at λ / 4 from both ends.

The piezoelectric transformer 20 shown in FIGS. 2A and 2B is manufactured as follows. First, PZT
An electrode strip electrode pattern is printed with a silver-palladium electrode paste on a 115 μm thick green sheet of piezoelectric ceramics, 10 layers of the printed sheet are laminated, and 1 layer of a ceramic green sheet having no electrode pattern is laminated thereon. The laminate was thermocompression bonded and sintered at 1150 ° C. in the atmosphere. Next, the silver paste is used to form the surface electrodes 22 and 23 facing each other in the thickness direction on the approximately half portion of the rectangular plate not including the internal strip electrode 26 in the length direction. 23 is connected to the side electrodes 24 and 25 on the side surface of the rectangular plate, respectively, at a position approximately at the center in the length direction,
Further, a strip-shaped external electrode 27 connected to the strip-shaped internal electrode 26 was formed on the side surface of the rectangular plate, and a piezoelectric transformer of 40 mm in length, 10 mm in width, and 1 mm in thickness in the lengthwise one-wavelength resonance mode was prototyped.

In the piezoelectric transformer according to the second embodiment of the present invention, since the nodes of the one-wavelength resonance mode are located 10 mm from the end faces in the length direction of the piezoelectric ceramic rectangular plate, the vicinity of the outside Electrode 27 and surface electrodes 22, 2
3 was supported, and each electrode was used as a lead-out / connecting portion. The polarization of piezoelectric ceramics is 150 ℃
The test was performed at an electric field strength of 1.2 kV / mm. The ceramic crystal grain size, mechanical and electrical performance of the piezoelectric transformer according to the second embodiment are shown in Table 1 below in comparison with the piezoelectric transformer having the conventional structure.

[0023]

[Table 1]

As is clear from Table 1 above, in the piezoelectric transformers according to the first and second embodiments of the present invention, by forming partial electrodes in the output section, the strain concentration at the time of polarization at the nodes of the output section can be concentrated. Compared with the piezoelectric transformer of the conventional structure, it is dispersed and prevents the generation of microcracks, and the three-point bending strength is three times or more, the initial failure rate is one-tenth or less, and the failure rate after driving for 1,000 hours is seven minutes. A highly reliable piezoelectric transformer of 1 or less was obtained.

[0025]

As described above in detail, according to the present invention, the ceramic rectangular plate serving as the piezoelectric transformer output portion, which is the concentrated portion of polarization distortion and the maximum portion of vibration distortion when the piezoelectric transformer is driven, is provided. A plurality of strip-shaped internal electrodes are provided at a quarter position in the length direction in a direction orthogonal to the length direction of the rectangular plate,
The band-shaped internal electrode is connected to the band-shaped external electrode on the side surface of the rectangular plate, so that the concentration of strain during polarization can be avoided,
It is possible to provide a highly reliable piezoelectric transformer with excellent mechanical characteristics.

[Brief description of drawings]

FIG. 1A is a perspective view of a piezoelectric transformer according to a first embodiment of the present invention. (B) is sectional drawing of the length direction of (a).

FIG. 2A is a perspective view of a piezoelectric transformer according to a second embodiment of the present invention. (B) is sectional drawing of the length direction of (a).

FIG. 3 is a schematic perspective view of a piezoelectric transformer using a conventional one-wavelength resonance mode piezoelectric vibrator.

FIG. 4A is a sectional view of the piezoelectric ceramic rectangular plate shown in FIG. (B) is a diagram showing a displacement distribution when the piezoelectric ceramic rectangular plate of (a) is vibrating in a longitudinal single wavelength resonance mode. (C) is a figure which shows the strain distribution at the time of the vibration of (b), respectively.

[Explanation of symbols]

 10, 20, 30 Piezoelectric transformer 11, 21, 31 Piezoelectric rectangular plate 12, 13, 22, 23, 32, 33 Surface electrode 15, 16, 27 External electrode 14, 26 Strip-shaped internal electrode 17, 28 Distribution of lines of electric force Dashed line 24,25 Side electrode 34,35 Strip surface electrode 41,41 'Vibration node

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Ono 6-7 Koriyama, Taichiro-ku, Sendai-shi, Miyagi Tokin Co., Ltd.

Claims (2)

[Claims] 1. A piezoelectric transformer using a resonance mode in a length direction of a piezoelectric rectangular plate made of a piezoelectric ceramic, the piezoelectric transformer being provided in approximately half the length direction of the piezoelectric rectangular plate and facing each other in the thickness direction. The pair of surface electrodes and the piezoelectric rectangular plate are provided at approximately one-fourth positions in the lengthwise direction of the piezoelectric rectangular plate at approximately the center of the other half of the lengthwise direction of the piezoelectric rectangular plate. 2. A piezoelectric transformer, comprising: a plurality of strip-shaped internal electrodes formed in a direction intersecting with a direction; and strip-shaped external electrodes provided on a side surface of the piezoelectric rectangular plate and connected to the strip-shaped internal electrodes. 2. The piezoelectric transformer according to claim 1, wherein
The surface electrodes are respectively connected to strip-shaped side surface electrodes provided on the side surfaces of the piezoelectric rectangular plate at positions approximately in the longitudinal direction, and the external electrodes are further connected to the internal surface of the piezoelectric rectangular plate. A piezoelectric transformer characterized in that it extends facing the electrodes.