JP3141575B2 - 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,
The present invention relates to a piezoelectric transformer that can make a substrate smaller and that can be stably supported at a peripheral portion of the substrate.

Conventionally, an electromagnetic transformer has been used to increase or decrease an AC voltage. This electromagnetic transformer has a structure in which a primary winding and a secondary winding are electromagnetically coupled via a magnetic core, and it is inevitable that the electromagnetic transformer occupies a considerably large volume.

In the field of information processing devices, CR
Devices that require a high voltage of several thousands V, such as a T display, and devices that output a large current, such as a DC-DC converter, are used. A transformer is indispensable in these devices, and miniaturization of the transformer is one of the issues.

[0004]

2. Description of the Related Art A piezoelectric transformer is provided with a primary electrode and a secondary electrode on a piezoelectric substrate and electrically and mechanically coupled to each other. A voltage is applied to the primary electrode to excite mechanical vibration on the piezoelectric substrate. This is a transformer that converts the vibration into a voltage at the secondary electrode.

FIG. 4 is a perspective view illustrating an example of a conventional piezoelectric transformer, and FIG. 5 is an explanatory view of the orientation of the crystal axis of a piezoelectric substrate. In the figure, 1 is a substrate, 2a and 2b are primary electrodes, 3
a and 3b are secondary electrodes, 6 is a support mechanism, and 10 is a piezoelectric transformer.

In FIGS. 4 and 5, the piezoelectric transformer 10 exemplified here is disclosed by the present inventors in Japanese Patent Application No. 2-2495.
The piezoelectric transformer 74 has already been proposed and utilizes the piezoelectric transverse effect of a piezoelectric body.

The substrate 1 has an L having a size of several mm × several tens mm.
A slice of a piezoelectric body of iNbO ₃ is used. In FIG. 5, among the crystal axes X, Y, and Z, a single crystal ingot of LiNbO ₃ uniformly polarized in the Z-axis direction is represented by a Z ′ axis corresponding to the longitudinal direction of the substrate, and the X-axis is the rotation axis. As θ = 140
° Cut to the rotated orientation. Then, the Y ′ axis corresponding to the direction perpendicular to the substrate 1 is also 140 ° with respect to the original Y axis.
It is spinning. The direction of the X axis corresponding to the lateral direction of the substrate 1 does not change. When such an orientation is selected and cut out, the polarization P becomes oblique to the longitudinal direction of the substrate 1, and the electromechanical coupling coefficient can be maximized.

On one half of the upper surface and the lower surface of the substrate 1,
Primary electrodes 2a and 2b are formed facing each other across the substrate 1,
An input voltage Vi for oscillating the substrate 1 is applied. Also,
Secondary electrodes 3a and 3b that convert the vibration of the substrate 1 into an output voltage Vo are formed on the other half of the substrate so as to face each other with the substrate 1 interposed therebetween. When the support mechanism 6 is provided at a position corresponding to the vibration node of the substrate 1 and is supported so that the substrate 1 can freely vibrate, the piezoelectric transformer 10 is completed.

[0009]

As described above, in the piezoelectric transformer utilizing the piezoelectric transverse effect, the polarization of the piezoelectric body need be performed only in a single direction, and the voltage ratio between the primary side and the secondary side is different from that of the primary side. It can be controlled by the area ratio of the secondary electrode. In addition, LiNbO ₃
If a piezoelectric single crystal is used, a large electromechanical coupling coefficient can be obtained.

However, since the electrodes are formed on the entire surface of the substrate and the side wall cut surface of the substrate cannot be used in order to avoid minute cracks, the shape of the substrate becomes large. Further, in order to freely vibrate the substrate, the periphery of the substrate cannot be touched. Therefore, it is necessary to provide a substrate support mechanism near the gap between the primary and secondary electrodes, and it is troublesome to stably support the structure.

Accordingly, an object of the present invention is to provide a piezoelectric transformer which can make a substrate smaller by utilizing "thickness shear vibration" of a piezoelectric body and can stably support an end of the substrate. .

[0012]

Means for Solving the Problems The above-mentioned problem is solved in FIG.
Has primary electrodes 2a and 2b and secondary electrodes 3a and 3b which are opposed to each other via a substrate 1 made of a piezoelectric material and are attached close to each other. Then, the primary electrodes 2a, 2b
Is for applying a primary-side AC voltage: Vi in the thickness direction of the substrate 1 to cause thickness-shear vibration, and the secondary-side electrodes 3a and 3b convert the thickness-shear vibration to a secondary-side AC voltage Vo. The problem is solved by a piezoelectric transformer configured to convert.

[0013]

[Function] A conventional piezoelectric transformer utilizing the piezoelectric lateral effect is:
Since longitudinal waves propagating in the longitudinal direction of the substrate were used, electrodes were applied to the entire surface of the substrate, and it was necessary to support the central portion of the substrate so as not to impair free vibration. In addition, the thickness shear vibration excited in the substrate when a voltage is applied in the thickness direction of the piezoelectric substrate is used. That is, a secondary electrode is provided in the center of the substrate to concentrate energy.

In this case, the primary electrode and the secondary electrode can be efficiently electromechanically coupled. Further, since the thickness direction of the substrate is used, the electrode can be provided in the center of the substrate to be small. Further, since the vibration energy confined in the central portion of the substrate is used, the peripheral portion of the substrate can be stably supported.

[0015]

FIG. 1 is a diagram for explaining an embodiment of the present invention.
(A) is a perspective view from the front side, FIG. 1 (B) is a perspective view from the back side, FIG. 1 (C) is a schematic view of energy distribution, and FIG. 2 is a first embodiment using LiNbO ₃ for the substrate. For example, FIG. 3 shows a second embodiment using LiTaO ₃ for the substrate. In the figure, 1 is a substrate, 2a and 2b are primary electrodes, 3a and 3b are secondary electrodes, 4 is an input terminal, 5 is an output terminal, 6 is a support mechanism, and 10 is a piezoelectric transformer.

In FIG. 1, a substrate 1 of a piezoelectric transformer 10 is made of a piezoelectric plate having mirror-polished surfaces on both sides and a thickness of 0.2 to 0.5 mm and a side of several mm, and when an AC voltage is applied in the thickness direction. Thickness shear vibration is caused. Then, on both surfaces of the substrate 1, the primary electrodes 2a and 2b and the secondary electrodes 3a and 3b are formed of metal thin films such as Au, respectively.

The primary electrodes 2a and 2b are formed on the input side of the transformer, and the secondary electrodes 3a and 3b are formed on the output side of the transformer. That is, the primary-side electrodes 2a and 2b are formed in the respective central portions of the substrate 1 in a frame shape with one side and one side opened, and the input terminals 4 are led out to the end portions of the substrate 1. Also, the secondary electrodes 3a, 3b are the primary electrodes 2a,
The output terminal 5 is formed at a central portion surrounded by 2b, and the output terminal 5 is led out to an end of the substrate 1.

A piezoelectric transformer having such an electrode configuration
Reference numeral 10 denotes that when a primary-side AC voltage: Vi is applied to the primary-side electrodes 2a and 2b, a particle displacement occurs in the substrate 1 as indicated by an arrow in FIG. And
As shown in FIG. 1C, the energy distribution of the thickness-slip vibration is concentrated at the center where the primary electrodes 2a and 2b and the secondary electrodes 3a and 3b are provided. That is, “entrapment of energy” occurs. Therefore, if the secondary electrodes 3a and 3b are provided at the center of the substrate 1 in which the energy is confined, the primary electrode
Electromechanical coupling between 2a, 2b and secondary electrodes 3a, 3b can be efficiently performed. Further, since the thickness-shear vibration involves the central portion of the substrate 1, the supporting mechanism 6 can be provided on the peripheral portion of the substrate 1, so that stable support is possible.

The relationship between the primary alternating voltage Vi applied to the primary electrodes 2a and 2b and the secondary alternating voltage Vo converted at the secondary electrodes 3a and 3b is as follows: Vi: primary electrode 2a, Primary side AC voltage applied between 2b and Vo: Secondary side AC voltage induced between secondary side electrodes 3a and 3b C ₁ : Capacitance between input terminals 4 C ₂ : Capacitance between output terminals 5 S ₁ : Area of the primary electrodes 2a, 2b S ₂ : Area of the secondary electrodes 3a, 3b If Vo / Vi∝C ₁ / C ₂ ────────── (1) C ₁ / C ₂ = S ₁ / S ₂ ────────── (2) Therefore, from the expressions (1) and (2), Vo / Vi∝S ₁ / S ₂ ────── ──── (3) That is, the secondary-side AC voltage Vo with respect to the primary-side AC voltage: Vi has a relationship inversely proportional to the area of the electrode.
Therefore, the secondary electrodes 3a, 3b disposed in the center of the substrate 1
If the area of the primary electrodes 2a and 2b surrounding the secondary electrodes 3a and 3b is increased and the area of the primary electrodes 2a and 2b surrounding the secondary electrodes 3a and 3b is increased, it is possible to obtain the piezoelectric transformer 10 that boosts the voltage. In addition, if the area ratio is reversed, the piezoelectric transformer 10 whose voltage is reduced can be obtained. As described above, it is possible to easily perform step-up / step-down by a simple means for changing only the area ratio.

Embodiment 1 In FIG. 2, the substrate 1 of the piezoelectric transformer 10 has LiNb
A 163 ° rotating Y-cut plate of O ₃ single crystal is used, and the substrate 1
Primary electrodes 2a and 2b and secondary electrodes 3a and 3b are respectively attached to both surfaces of the substrate. The orientation of the crystal axis of the substrate 1 is obtained by rotating the Y axis by 163 ° with the X axis being parallel to the lateral direction of the substrate 1 as the rotation axis, making the Y ′ axis perpendicular to the substrate 1 and the Z ′ axis It is cut so as to be parallel to the longitudinal direction.

In the substrate 1 made of LiNbO _{3 having} this cut orientation, a high electromechanical coupling coefficient of 62% can be obtained. Embodiment 2 In FIG. 3, the substrate 1 of the piezoelectric transformer 10 is made of LiTa.
An X-cut plate of O ₃ single crystal is used, and primary electrodes 2a and 2b and secondary electrodes 3a and 3b are respectively attached to both surfaces of the substrate 1. The orientation of the crystal axis of the substrate 1 is obtained by rotating the Y axis and the Z axis by -48 ° with the X axis perpendicular to the substrate 1 as the rotation axis, and
The axis is cut parallel to the longitudinal direction of the substrate 1 and the Z ′ axis is cut parallel to the lateral direction of the substrate 1.

In the substrate 1 made of LiTaO _{3 having} this cut orientation, a high electromechanical coupling coefficient of 47% can be obtained. As the piezoelectric material constituting the substrate 1, a piezoelectric ceramic can be used in addition to the single crystal exemplified here. However, the piezoelectric single crystal has more excellent characteristics in that the electromechanical coupling coefficient is large, the loss is small, the input impedance is low, and a large current can be obtained.

[0023]

According to the present invention, since the thickness shear vibration excited in the substrate when a voltage is applied in the thickness direction of the piezoelectric substrate is used, the electrode is provided at the center of the substrate. Can be smaller. In addition, since the vibration energy confined in the central portion of the substrate is used, electromechanical coupling can be efficiently performed with a simple electrode configuration, and the end portion of the substrate can be stably supported. Furthermore, the shape of the electrodes is simple, and the input voltage can be increased or
The buck can be controlled.

In this way, it is possible to realize a small-sized piezoelectric transformer instead of an electromagnetic transformer, and the present invention provides a compact, light-weight, and chipless transformer which has been intact as electronic components have become chipped. The place that contributes is great.

[Brief description of the drawings]

1A and 1B are diagrams illustrating an embodiment of the present invention, wherein FIG. 1A is a perspective view as viewed from a front side, FIG. 1B is a perspective view as viewed from a back side,
(C) is a schematic diagram of an energy distribution.

FIG. 2 is a first embodiment using LiNbO ₃ for a substrate.

FIG. 3 is a second embodiment using LiTaO ₃ for the substrate.

FIG. 4 is a perspective view illustrating an example of a conventional piezoelectric transformer.

FIG. 5 is an explanatory diagram of an orientation of a crystal axis of a piezoelectric substrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2a, 2b Primary electrode 3a, 3b Secondary electrode 4 Input terminal 5 Output terminal 6 Support mechanism 10 Piezoelectric transformer

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Noboru Wakatsuki 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Inside Fujitsu Limited (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 41/08

Claims (2)

(57) [Claims] 1. Primary electrodes (2a), (2) opposed to each other via a substrate (1) made of a piezoelectric material and applied close to each other.
b) and secondary electrodes (3a) and (3b), and the secondary electrode (3
a) and (3b) are locally disposed in the center of the substrate (1).
And the primary electrodes (2a) and (2b) are the secondary electrodes.
(3a) A piezoelectric transformer which is provided in a frame shape around (3b) . 2. The method according to claim 1, wherein the substrate (1) is LiNbO3 or LNbO3.
2. The piezoelectric transformer according to claim 1, comprising a piezoelectric single crystal of iTaO3.