JPS58119215A - Electrode construction of piezoelectric oscillator - Google Patents

Abstract

PURPOSE:To decrease the value of a crystal impedance (CI) of an oscillator operated in the thickness bending oscillation mode, by providing metallic thin film electrodes having electric polarity and a metallic thin film electrode not connected to any electric polarity. CONSTITUTION:The metallic thin film electrodes having different electric polarity are taken as the 1st and the 2nd electrodes and the polarity of an electric terminal 40 is ositive and that of an electric terminal is negative. Further, the other electrode 19 (3rd electrode) not connected to any of the 1st and 2nd electrodes is provided. The distriution of electric line of force of the 1st and the 2nd electrodes is changed by providing the 3rd electrodes 19. That is, the electric line of force 50 from the 1st electrode enters one end of the 3rd electrode 19 once and starts from the other end of the 3rd electrode 19 and enters again the 2nd electrode. As a result, the distribution of the electric line of force 50 is much in the vicinity of the surface of the oscillator 1, an effective electric field component Ex is increased and an ineffective electric field component Ez is decreased. Thus, the CI value of the oscillator 1 is smaller when the 3rd electrode is provided than in the case otherwise.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrode structure of a piezoelectric vibrator, particularly a crystal vibrator, which vibrates in a thickness bending vibration mode.

A metal thin film electrode is fixed to the surface of the crystal resonator to electrically excite the resonator. Generally, the electrode structure is designed to reduce the crystal impedance (CI value) of the crystal resonator.

When exciting a two-plate crystal oscillator in thickness bending vibration mode,
Conventional electrode structures have the disadvantage that it is difficult to increase the effective electric field component, resulting in a large CI value of the vibrator.

The object of the present invention is to propose an electrode structure that does not have the above-mentioned drawbacks. In order to achieve this object, the present invention provides a piezoelectric vibrator excited in a thickness bending vibration mode, in which a metal thin film electrode having electrical polarity and a metal thin film electrode not electrically connected to either polarity are used. 0 Below, embodiments of the present invention will be described in detail while comparing them with conventional examples.

FIG. 1 is a perspective view of a rectangular two-plate crystal resonator according to the prior art and the present invention. The X, Y, and Z axes indicate the electrical, mechanical, and optical axes of the crystal, respectively.

Figure 2 is an explanatory diagram of the vibration mode when a rectangular two-plate crystal resonator vibrates in the thickness bending primary vibration mode.
Shown when viewed from the direction. The vibrator 1 comes to the position 2 shown by the dotted line at a time (1/4) period after the time when the vibration displacement becomes zero. FIG. 3 is a cross-sectional view perpendicular to the Y-axis showing the distribution of normal stress δy in the X-direction along the plate thickness direction (two directions) in the thickness bending vibration mode. As shown by arrow 6, stress σy is distributed almost linearly along two directions,
The sign of the stress σy is reversed between the upper half and the lower half of the plate thickness.

According to the basic piezoelectric formula of crystal, there is a relationship between stress σy and electric field component EX in the X direction as shown in the following formula 0 σ3'=-1a 11 Ez... (1) Here, eu: piezoelectric constant From FIG. 3 and equation (1), excitation of the thickness bending vibration mode requires electric field components Ex in different directions in the upper and lower halves of the vibrator 1. The electric field component Ex needs to be distributed as close to the surface of the vibrator 10 as possible.

FIGS. 4(A), 4(B), and 4(C) are cross-sectional views perpendicular to the Y-axis showing examples of conventional electrode structures in a two-plate crystal resonator.

For the sake of simplicity, the following describes the electrical conductivity of metal thin films with different electrical polarities. In FIG. 4(A), a first electrode 4 and a second electrode 5 are fixed to the top surface of the camera element 1, and the electric field component Ex of the electric line of force 6 passing through the upper half of the camera element 1 is the excitation force. However, the electric field component Ex of the lines of electric force 7 passing through the lower half has the same sign as the electric field component in the upper half, so it acts as a resistive force. Therefore, with this electrode structure, the CI value becomes considerably large. In Figure 4 (B),
A first electrode 8.9 and a second electrode 10.11 are fixed to the upper and lower surfaces of the vibrator 1, and effective lines of electric force 12.16 are slightly generated in the upper and lower halves of the vibrator 1. do.

However, there are many reactive electric lines of force 14, and the CI value of the vibrator 1 does not become small. In FIG. 4(C), the first electrode 15.
16. Second electrodes 17 and 18 are fixed to both sides of the vibrator 1, and necessary components Ex are generated near the sides in the upper half and lower half of the plate thickness, respectively.

Although this electrode structure has a smaller CI value than the two examples above, the CI value is not sufficient.
)(C) is an explanatory diagram of a cross section perpendicular to the Y axis of an electrode structure showing an embodiment of the present invention in a two-plate crystal resonator. Fifth
Figures (A), (B), and (C) all show other electrodes 1 that are not electrically connected to either the first electrode or the second electrode.
9 (hereinafter referred to as the third pole for simplicity) is created. By providing the third electrode 19, the distribution of electric lines of force between the first electrode and the second electrode changes. That is, the electric force line 50 coming out of the first electrode once enters one end of the third electrode 19, comes out again from the other end of the third electrode 19, and enters the second electrode. As a result, many lines of electric force 50 are distributed near the surface of the vibrator 1, and the effective electric field component E
x increases, and the invalid electric field component KZ decreases. Therefore, the CI value of the vibrator 1 is smaller when the third electrode is present than when it is absent.

Next, a case will be described in which the electrode structure of the present invention is applied to an I-type two-plate crystal resonator. FIG. 6 is a perspective view of an E-type two-plate crystal resonator according to the present invention. When an E-type two-plate crystal oscillator vibrates in the thickness bending vibration mode, assuming that the vibration techniques 21 and 26 on both sides of the vibrator 20 are in phase and displaced in the +Z direction, the vibration technique 22 in the middle is displaced in the -2 direction. Displaced to. arrow 2
4.2526 shows these relationships. Figure 7 (A) (B
)(C) is a perspective view of an electrode structure according to an embodiment of the present invention in an E-type two-plate crystal resonator. FIG. 7(A) shows the first electrode 7
1a, the second electrode 72a and the third electrode 73a are the vibrator 2U
This shows the case where it is provided only on the top surface. Figure 7 CB
) are the first electrode 71b, the second electrode 721) and the third electrode 7
31) are provided on the upper and lower surfaces of the vibrator 20. FIG. 7(C) shows a case where the first electrode 71c and the second electrode 72C75f are provided on the side surface of the movable element 2U, and the third electrode is provided on the top and bottom surfaces of the vibrator 20. Figure 8 (A) (B) (C) is Figure 7 (A)
(B) The AA sectional view of (C) shows the connection state of the first electrode and the second electrode provided in each vibration technique.

When the electric terminal 80 is positive and the electric terminal 81 is negative, electric lines of force as shown by arrows 82 are generated in each vibration technique, and the vibrator 20 is stored in the bending primary vibration mode. It can be made to vibrate.

At this time, the CI value of the vibrator 20 becomes a relatively small value thanks to the third electrode.

In the above explanation, the crystal resonator is limited to the Z plate, but
In general, the electrode structure of the present invention is also effective with a rotating Z plate, that is, with two plates rotated by a certain angle around the X axis. More generally, the present invention is effective for thickness-bending crystal resonators that are excited by electric field components that are antiparallel to each other in the upper and lower halves of the plate thickness, regardless of the cut orientation.

Further, the present invention is not limited to crystal as the material of the vibrator, but is also effective in other piezoelectric materials such as ceramics, lithium tantalate, etc.

According to the present invention, the CI value of a vibrator operating in the thickness bending vibration mode can be reduced by relatively simple means. is especially large.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a rectangular two-plate crystal resonator according to the prior art and the present invention. Figure 2 shows thickness bending 1 in a rectangular two-plate crystal sensor.
Fig. 3 is a cross-sectional view perpendicular to the X-axis of the next vibration mode, and Fig. 4 is a cross-sectional view perpendicular to the )(
B) (C) is an explanatory diagram of a cross section perpendicular to the Y axis of a conventional electrode structure in a rectangular two-plate crystal resonator;
)(C) is an explanatory diagram of a cross section perpendicular to the Y axis of the electrode structure of the embodiment of the present invention in a rectangular two-plate crystal resonator, and FIG. 6 is a perspective view of an E-type crystal resonator according to the conventional and the present invention. Figure 7 (A)
(B) (C) are perspective views of the electrode structure showing an embodiment of the present invention in an E-type two-plate crystal resonator; FIG. 8 (A) ω) (C)
FIG. 7 is an explanatory diagram showing the connection of the first electrode and the second electrode as seen from the AA cross section in FIGS. 7(A), 7(B), and 7(C). 1... Rectangular 2-plate crystal oscillator 4.8.9.15.16.71a, 71b, 71cm・
First electrode 5, 10.11.17.1a, 72a, 7
2b, 72c...-second electrode 6.7.12.16.
14.50,82...Electric force lines 19.7,6a,7
3b, 76cm ・Third electrode 20... E-type two-plate crystal oscillator Figure 1 Figure 4 (A) CB) Figure 2 (C) Figure 7 (C)

Claims (1)

[Claims] Piezoelectric vibration characterized in that the electrode structure of a piezoelectric vibrator excited in a thickness bending vibration mode includes a metal thin film electrode having electrical polarity and a third electrode that is not electrically connected to either polarity. Child electrode structure.