JP3362344B2 - Piezo device - 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 device using a lithium niobate single crystal, and particularly, a piezoelectric vibration utilizing a Lame mode vibration of a piezoelectric rectangular plate which can be easily supported and can efficiently operate at a resonance point. The present invention relates to a piezoelectric device such as a child, a piezoelectric transformer and a piezoelectric filter.

[0002]

2. Description of the Related Art There are many devices that do not require a large current value but require a high voltage of about 1 kV for lighting a backlight of a liquid crystal display or charging a toner of a copying machine.
Currently, electromagnetic transformers are generally used to excite high voltages. However, due to demands such as reduction of generated electrode noise, low power consumption, downsizing of equipment, and low profile, practical application of piezoelectric transformers is being investigated. Has been done. Conventional piezoelectric transformers generally use piezoelectric ceramics for piezoelectric vibrators, but in recent years lithium niobate single crystals have been used for reasons such as high resonance sharpness Q, high boosting capability, less heat generation, and safety. The investigation of the piezoelectric transformer used is being actively pursued. Here, a schematic view of a piezoelectric vibrator of a piezoelectric transformer using lithium niobate is shown in FIG. In FIG. 7, an input electrode 62 and an output electrode 63 are formed on the front surface and a ground electrode 64 is formed on the rear surface of a rectangular substrate 61 of lithium niobate single crystal. With this piezoelectric vibrator, a boosting ratio of 500 or more is possible. For example, the output voltage when the input voltage is 2V is 1 kV or more.

[0003]

Generally, a piezoelectric vibrator or a piezoelectric transformer, which is a piezoelectric device, has a resonance sharpness (Q).
It is desirable to support at the node of vibration so as not to cause the decrease of the resonance frequency and the change of the resonance frequency.

In the piezoelectric transformer using the conventional lithium niobate single crystal shown in FIG. 7, a high step-up ratio is obtained,
Since the four corners of the rectangular plate 61 are used as nodes, it is necessary to excite the oscillator in the vicinity of the Lame mode resonance point. That is, FIG.
In the case of a piezoelectric vibrator that uses an in-plane isotropic rectangular plate, such as the piezoelectric transformer shown in, when the vertical and horizontal dimension ratios are integer ratios,
There is in-plane vibration called the Lame mode in which the four corners do not vibrate, and using this vibration mode facilitates support.
However, even when the piezoelectric vibrator is well supported, the resonance sharpness (Q) of the lithium niobate single crystal is 1 or less.
It is very large as 0000 or more, and there is a drawback that the boosting efficiency is significantly reduced if the frequency at the time of excitation deviates even a little from the frequency at the resonance point. Even if the frequency at the time of excitation is well matched to the frequency at the resonance point, the frequency at the resonance point shifts due to ambient temperature changes, heat generation of the vibrator, etc., and the boosting efficiency of the piezoelectric transformer is increased. It had a fatal drawback of being significantly reduced.

Therefore, a technical problem of the present invention is to provide a piezoelectric vibrator which is easy to support and does not deteriorate the characteristics, and which prevents deviation of the resonance frequency at the time of excitation and which is efficient and has excellent characteristics. It is to provide a piezoelectric device provided with.

[0006]

According to the present invention, the orthogonal polarization system (X, Y, Z) is used to set the spontaneous polarization axis of the lithium niobate single crystal as the Z axis, and the coordinate axis is used as the Z axis reference. Cartesian coordinate system (X ', Y', Z ') rotated by 120 to 170 degrees around the X axis, and -2 around the Z'axis.
0 to 20 ° rotated orthogonal coordinate system (X', Y〃, Z ') in the plate plane X' made of single-crystal plate cut in parallel to the Z 'axis as the axis, vertical and horizontal The single crystal plate having a shape in which one or two or more square plates having substantially equal dimensional ratios are arranged vertically and horizontally is configured to vibrate in Lame mode vibration in which the four corners of the square plate are nodes of vibration. A piezoelectric device including a piezoelectric vibrator , wherein the piezoelectric vibrator includes an input electrode for inputting an electrical signal,
A piezoelectric device having an output electrode for outputting an electric signal and at least one signal electrode for extracting an electric signal, which is different from the input electrode and the output electrode, is obtained. .

According to the present invention, in the piezoelectric device, at least one of the vibration nodes of the piezoelectric vibrator is supported, and the input node, the output electrode, and the signal electrode are provided at the vibration node. A piezoelectric device is obtained which is characterized by being connected as an input terminal, an output terminal, and a signal terminal, respectively.

According to the present invention, in the piezoelectric device, the single crystal plate is provided with a vertical to horizontal dimensional ratio of 1: 2,
In the piezoelectric vibrator, electrode films are formed on both front and back surfaces of the single crystal plate, and at least one of the formed electrode films is divided into two to form the input electrode and the output electrode. And the output electrode is extended to any of the vibration nodes to form the input terminal and the output terminal, respectively, and the signal electrode is connected to the vibration node other than the input terminal and the output terminal. A piezoelectric device is obtained, which is a rectangular plate Lame mode oscillator having the signal terminal formed by extending to any one of them.

According to the present invention, in any one of the piezoelectric devices, a self-excited oscillating circuit that operates at a resonance point of the piezoelectric device is configured by using the input electrode and the signal electrode, and the self-excited oscillation circuit is formed. A piezoelectric device is obtained which is characterized in that a signal from an oscillation circuit is input to the input electrode to efficiently excite and operate at a resonance point.

[0010]

In the present invention, since the electric signal is taken out from the signal electrodes other than the input electrode and the output electrode of the vibrator actually excited and inputted to the input electrode through the self-excited oscillation circuit, the Lame mode resonance point It becomes possible to excite very efficiently. Further, even if the frequency at the resonance point is shifted, the frequency at the resonance point can be automatically tracked.

[0011]

EXAMPLES Examples of the piezoelectric transformer, which is one of the piezoelectric devices of the present invention, will be described below in detail with reference to the drawings.

FIG. 1 is a perspective view showing an example of the structure of a piezoelectric transformer according to an embodiment of the present invention. As shown in Figure 1,
The piezoelectric transformer is a rectangular plate 11 cut out from a lithium niobate single crystal and having an aspect ratio of 1: 2.
Input electrode 12a formed of two-divided electrodes formed on one surface of No. 1
And an output electrode 12b, a signal electrode 13 for extracting a signal for the self-oscillation circuit, and a ground electrode 15 formed on the other surface of the rectangular plate 11 opposite to the one surface. Further, the self-excited oscillation circuit 14 is connected to the input electrode 12 a and the signal electrode 13.

FIG. 2 is a circuit diagram showing an example of the self-excited oscillation circuit 14 shown in FIG. As shown in FIG. 2, the self-excited oscillation circuit 14 includes two transistors Q1 and Q2, two variable resistors VR1 and VR2, and three capacitors C1 to C3.
And five resistors R1 to R6.

The signal electrode 13 is connected to the base of the transistor Q1 via the capacitor C1. The base is connected to the input terminal via the resistor R1 and is connected to the ground terminal 16b via the resistor R2. The collector of the transistor Q1 is connected to the input terminal R3 via the resistor R3 and the capacitor C
3 is connected to one end. The emitter of the transistor Q1 is connected to the ground terminal 16b via the parallel resonance circuit of the variable resistor VR1 and the capacitor C2.

The input electrode 12a is connected to one end of the resistor R4 and the collector side of the transistor Q2, and the other end of the resistor R4 is connected to the input terminal 16a. One end of the resistor R6 is connected to the base side of the transistor Q2, and the other end of the resistor R6 is connected to a connection portion between the resistor R5 connected to the input terminal 16a and the variable resistor VR2 connected to the ground terminal, The connecting portion is further connected to the other end of the capacitor C3. The emitter of the transistor Q1 is connected to the ground terminal 16b. The ground electrode is connected to the ground terminal 16b.

An example of these circuit elements is VR
1 = 1 kΩ, VR2 = 5 kΩ, C1 = C3 = 0.01 μ
F, C2 = 1 μF, R1 = R2 = R5 = 5.1 kΩ, R
3 = R6 = 1 kΩ and R4 = 470Ω.

FIG. 3 is a plan view showing an example of a state in which the electrodes of the piezoelectric transformer shown in FIGS. 1 and 2 are taken out and supported. As shown in FIG. 3, the input electrode 12a, which is a two-divided electrode formed on one surface of the rectangular plate 11 cut out from the lithium niobate single crystal, and the conductive films 21 and 22 are extended from the output electrode to the corners. The input terminal 16a and the output terminal 17a are formed by being supported by a metal support plate 24 and a conductor 25 formed at the corners of an insulating support frame. Similarly, in the signal electrode 13, the conductive film 25 is also formed to extend to the corner portion and is supported by the metal supporting plate 24 and the conductor 25. The ground electrode formed on the back surface of the rectangular plate 11 (not shown) is also formed to extend to the corners, and the metal supporting plate 24
And the conductor 25 forms the ground terminal 16b (17b).

Here, in general, it is desirable that the piezoelectric vibrator or the piezoelectric transformer is operated at a vibration node so that the resonance sharpness (Q) is not lowered and the resonance frequency is not changed.

FIGS. 4, 5 (a), 5 (b) and 5 (c) are diagrams showing the Lame mode vibration of various rectangular plates of the piezoelectric vibrator used in the embodiment of the present invention. As shown in Figs. 4 and 5, in a rectangular plate made of a plate of isotropic in-plane lithium niobate single crystal, a plane called Lame mode in which the four corners do not vibrate when the vertical and horizontal dimension ratios are integer ratios. There is internal vibration, and if this vibration mode is used, it is easy to support. However,
Even if the support is successful, as mentioned above,
The resonance sharpness (Q) of a single crystal of lithium niobate is 100.
It is very large as 00 or more, and there is a drawback that the boosting efficiency will be significantly reduced if the frequency during excitation deviates even slightly from the frequency at the resonance point. If the frequency during excitation is well matched to the frequency at the resonance point However, due to changes in the ambient temperature, heat generated by the oscillator, etc., the frequency at the resonance point shifts, and the characteristics deteriorate, so it was necessary to always excite near the resonance frequency.

In the piezoelectric vibrator according to the embodiment of the present invention, the input electrode 12a and the output electrode 12b of the vibrator actually excited are used.
Since an electric signal is taken out from the other electrodes, that is, the signal electrode 13 and inputted to the input electrode 12a through the self-oscillation circuit, it is possible to excite very efficiently at the Lame mode resonance point. In addition, even if the frequency at the resonance point shifts, the frequency at the resonance point is automatically tracked.

A specific example of manufacturing the piezoelectric transformer according to the embodiment of the present invention will be described below.

Using a commercially available lithium niobate single crystal,
155 ° centered on the X-axis with reference to the spontaneous polarization axis (Z-axis)
Rotate, and further rotate 5 ° around the Z'axis which is orthogonal to the X axis, and measure 10 mm x 20 mm in the vertical and horizontal dimensions and 0.5 in thickness.
A square plate 11 of mm was cut out. Aluminum is vapor-deposited on one surface of the rectangular plate 11 to form a square ground electrode 15 having a size of 9 mm × 19 mm, and the other surface is also spaced by 1 mm from the periphery to have an electrode interval of 1 mm, and the size is 8.5 mm × 8.5 mm.
The two electrodes were formed side by side. Furthermore, 8.5 mm ×
One part of the 8.5 mm electrode was divided to form the signal electrode 13 for the self-oscillation circuit, and the other part except the divided part was used as the input electrode 12a. Also, 8.5 mm x 8.5 m
The other electrode of m was used as the output electrode 12b. Next, the metal plate 24 and the conductor 2 supporting the four corners of the rectangular plate on which the electrodes are formed.
5 is fixed to a supporting frame 23 having an electrode terminal and a metal plate 24.
And the self-excited oscillation circuit 1 connected through the support portion of the conductor 25.
A piezoelectric transformer including 4 was used. The electrical characteristics before and after the support are shown in Table 1 below.

[0023]

[Table 1]

As shown in Table 1 above, the resonance sharpness changes little before and after the support.

An input electrode 1 of 8.5 mm × 8.5 mm, which is partly divided from the signal electrode 13 for the self-oscillation circuit 14,
2a as an input terminal, the other 8.5 mm x 8.5
mm output electrode 12b as an output terminal and self-excited oscillation circuit 14
Table 2 below shows the measurement results of the input voltage and the output voltage and the step-up ratio in the case of excitation via the.

[0026]

[Table 2]

As shown in Table 2 above, it can be seen that the step-up ratio is almost constant even when the input voltage changes.

FIG. 6 is a diagram showing a change in the output voltage when the difference between the presence and absence of the self-excited oscillation circuit is compared by changing the ambient temperature. A curve 51 indicates the embodiment of the present invention having the self-excited oscillation circuit. In the piezoelectric transformer according to the example, the curve 52 is the case without the self-excited oscillation circuit.

As shown in FIG. 6, the piezoelectric transformer (curve 51) according to the embodiment of the present invention clearly has a constant boosting ratio as compared with the piezoelectric transformer (curve 52) having no self-oscillation circuit. I understand.

[0030]

As described above, according to the lithium niobate single crystal piezoelectric device utilizing the Lame mode vibration of the present invention, the support is easy and the characteristics are not deteriorated.
Moreover, it is possible to obtain a piezoelectric device such as a piezoelectric vibrator, a piezoelectric transformer, and a piezoelectric filter, which is highly efficient and has excellent characteristics, by sufficiently preventing the resonance frequency from shifting during excitation.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a self-excited oscillation circuit used in the piezoelectric transformer of FIG.

FIG. 3 is a plan view showing a state in which electrodes of the piezoelectric vibrator of FIGS. 1 and 2 are taken out and supported.

FIG. 4 is a diagram showing the lowest-order Lame mode vibration of a vibrator using a square plate.

5 (a), (b) and (c) are diagrams showing Lame mode vibrations of a vibrator having various rectangular plates.

FIG. 6 is a diagram showing a temperature characteristic of a step-up ratio of a piezoelectric transformer according to an example of the present invention, and also shows a temperature characteristic of a step-up ratio of a piezoelectric transformer according to a comparative example having no self-excited oscillation circuit.

FIG. 7 is a diagram showing an example of a conventional piezoelectric vibrator or piezoelectric transformer.

[Explanation of symbols]

11 square plate 12a input electrode 12b output electrode 13 signal electrode 14 Self-oscillation circuit 15 Earth electrode 21,22,26 Conductive film 24 Support plate 25 conductor 23 Support frame 61 square plate 62 input electrodes 63 Output electrode 64 ground electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-5-114492 (JP, A) JP-A-4-124886 (JP, A) JP-A-4-127486 (JP, A) JP-A-5- 299968 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 41/107

Claims (4)

(57) [Claims] 1. A Z-axis is defined as a spontaneous polarization axis of a lithium niobate single crystal using an orthogonal coordinate system (X, Y, Z).
As an axis reference, the coordinate axis is 120 to 170 around the X axis.
In the Cartesian coordinate system (X ', Y', Z ') rotated by °, and in the Cartesian coordinate system (X', Y〃, Z ') rotated by -20 to 20 ° around the Z'axis, the plate surface is X 'axis and the Z' single crystal plate Tona cut so as to be parallel to the axis
The Lame mode vibration in which the four corners of the square plate are vibration nodes of the single crystal plate having one or two or more square plates arranged vertically and horizontally such that the dimension ratios of the length and width are almost equal to each other. A piezoelectric device including a piezoelectric vibrator configured to perform, wherein the piezoelectric vibrator includes an input electrode for inputting an electric signal, an output electrode for outputting an electric signal, and the input terminal. A piezoelectric device, which is different from an electrode and the output electrode, and has at least one signal electrode for taking out an electric signal. 2. The piezoelectric device according to claim 1, wherein
At least one of the vibration nodes of the piezoelectric vibrator is supported, and the input node, the output electrode, and the signal electrode are connected to the vibration node to respectively input, output, and A piezoelectric device characterized by being a signal terminal. 3. The piezoelectric device according to claim 2, wherein
The single crystal plate has a vertical to horizontal dimensional ratio of 1: 2, and the piezoelectric vibrator forms electrode films on both front and back surfaces of the single crystal plate, and at least one of the formed electrode films is formed. Divided into two, forming the input electrode and the output electrode, extending the input electrode and the output electrode to any of the nodes of the vibration to form the input terminal and the output terminal respectively, A piezoelectric device, which is a rectangular plate Lame mode oscillator formed by extending the signal electrode to any one of vibration nodes other than the input terminal and the output terminal to form the signal terminal. 4. The piezoelectric device according to claim 1, wherein the input electrode and the signal electrode are used to operate at a resonance point of the piezoelectric device. And a signal of the self-oscillation circuit is input to the input electrode to efficiently excite and operate at a resonance point.