JPH0338770B2 - - Google Patents

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 for electrically exciting the vibrator is fixed to the surface of the crystal vibrator. Generally, the electrode structure is designed to reduce the crystal impedance (CI value) of the crystal resonator.

When a Z-plate crystal resonator is excited in the thickness bending vibration mode, the conventional electrode structure has the disadvantage that the CI value of the resonator increases because it is difficult to increase the effective electric field component.

The object of the present invention is to propose an electrode structure that does not have the above-mentioned drawbacks. to this end,
The present invention is a piezoelectric vibrator excited in a thickness bending vibration mode, which is characterized by having a metal thin film electrode having electrical polarity and a metal thin film electrode not electrically connected to either polarity. be.

Embodiments of the present invention will be described in detail below while comparing them with conventional examples.

FIG. 1 is a perspective view of a rectangular Z-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.

FIG. 2 is an explanatory diagram of the vibration mode when the rectangular Z-plate crystal resonator vibrates in the thickness bending primary vibration mode, and is shown when viewed from the X direction of FIG. 1. The vibrator 1 comes to 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 X-axis showing the distribution of σy in the y-direction along the plate thickness direction (Z-direction) in the thickness bending vibration mode. As shown by arrow 3, the stress σy is Z
The stress σy is distributed almost linearly along the direction, and the sign of the stress σy is reversed between the upper and lower half of the plate thickness.

According to the fundamental piezoelectric equation of crystal, there is a relationship between stress σy and electric field component Ex in the x direction as shown in the following equation.

σy=-e11Ex...(1) where e11: Piezoelectric constant From Figure 3 and equation (1), it is clear that for excitation of the thickness bending vibration mode, electric fields are applied to the upper and lower halves of the vibrator 1 in different directions. The component Ex is required, and the electric field component
Ex needs to be distributed as close to the surface of the vibrator 1 as possible.

4A, B, and C are cross-sectional views perpendicular to the Y-axis showing examples of conventional electrode structures in a Z-plate crystal resonator. For the sake of simplicity, metal thin film electrodes with different electrical polarities will be referred to as a first electrode and a second electrode to distinguish them below.
Further, it is assumed that the electric terminal 40 is positive and the electric terminal 41 is negative. In FIG. 4A, a first electrode 4 and a second electrode 5 are fixed to the top surface of the vibrator 1, and the electric field component Ex of the electric lines of force 6 passing through the top half of the vibrator 1 contributes to the excitation force. , the electric field component Ex of the electric line of 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 resistance force. Therefore, with this electrode structure, the CI value becomes quite large. In FIG. 4B, the first electrodes 8, 9 and the second electrodes 10, 11 are fixed to the upper and lower surfaces of the vibrator 1, and the effective lines of electric force 12 are in the upper and lower halves of the vibrator 1. , 13 occur slightly. However, there are many invalid electric lines of force 14,
The CI value of vibrator 1 does not become small. In FIG. 4C, first electrodes 15, 16, second electrodes 17, 18
are fixed to both sides of the vibrator 1, and the necessary components Ex
occurs near the sides. Although this electrode structure has a smaller CI value than the two electrode structures described above, the CI value is not sufficient.

5A, B, and C are explanatory diagrams of a cross section perpendicular to the Y axis of an electrode structure showing an embodiment of the present invention in a Z-plate crystal resonator. In each of FIGS. 5A, B, and C, another electrode 19 (hereinafter referred to as the third electrode for simplicity) that is not electrically connected to either the first electrode or the second electrode is provided. ing. 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 line of force 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, electric field lines 50
becomes more distributed near the surface of the vibrator 1, the effective electric field component Ex increases, and the invalid electric field component Ez decreases. Therefore, the oscillator 1
The CI value 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 E-type Z-plate crystal resonator. FIG. 6 is a perspective view of an E-type Z-plate crystal resonator according to the present invention. When the E-type Z-plate crystal resonator vibrates in the thickness bending vibration mode, when the vibrating branches 21 and 23 on both sides of the vibrator 20 are in phase and displaced in the +Z direction, the middle vibrating branch 22 is displaced in the -Z direction. Displaced to. arrow 24,2
5 and 26 indicate 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 Z-plate crystal resonator. FIG. 7A shows a case where a first electrode 71a, a second electrode 72a, and a third electrode 73a are provided only on the top surface of the vibrator 20. FIG. 7B shows the first electrode 71b and the second electrode 72b.
A case is shown in which third electrodes 73b are provided on the upper and lower surfaces of the vibrator 20. Figure 7 C is the first
The case is shown in which the electrode 71c and the second electrode 72c are provided on the side surface of the vibrator 20, and the third electrode is provided on the top and bottom surfaces of the vibrator 20. Figures 8A, B, and C are AA cross-sectional views of Figure 7A, B, and C.
The connection state of the first electrode and the second electrode provided on each vibrating branch is shown. Electrical terminal 80 is positive,
When the electric terminal 81 is negative, electric lines of force as shown by arrows 82 are generated in each vibrating branch, and the vibrator 20 can be vibrated in the thickness bending primary vibration mode. At this time, the vibrator 20
The CI value is relatively small due to the third electrode.

In the above description, the crystal resonator has been limited to a Z plate, but the electrode structure of the present invention is generally effective even with a rotating Z plate, that is, a Z plate 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 invention, by relatively simple means,
Since the CI value of a vibrator operating in the thickness bending vibration mode can be reduced, the effect of the present invention is particularly great in fields such as electronic watches that require low power supply voltage operation.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a rectangular Z-plate crystal resonator according to the prior art and the present invention. Figure 2 is a cross-sectional view perpendicular to the X-axis of the primary thickness-bending vibration mode in a rectangular Z-plate crystal resonator, and Figure 3 shows the distribution of normal stress σy in the y direction along the plate thickness direction in the thickness-bending vibration mode. show x
4A, B and C are explanatory diagrams of a cross section perpendicular to the Y axis of a conventional electrode structure in a rectangular Z-plate crystal resonator, and FIGS. 5A, B and C are rectangular Z 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 plate crystal resonator, FIG. 6 is a perspective view of an E type Z plate crystal resonator according to the conventional and the present invention, and FIG.
B and C are perspective views of an electrode structure showing an embodiment of the present invention in an E-type Z-plate crystal resonator, and FIGS. 8A, B, and C are
7 is an explanatory diagram showing the connection of the first electrode and the second electrode as seen from the AA cross section of FIGS. 7A, B, and C. FIG. 1... Rectangular Z-plate crystal oscillator, 4, 8, 9, 1
5, 16, 71a, 71b, 71c...first electrode, 5, 10, 11, 17, 18, 72a, 72
b, 72c...second electrode, 6, 7, 12, 13,
14, 50, 82... Lines of electric force, 19, 73a,
73b, 73c...Third electrode, 20...E type Z plate crystal resonator.

Claims (1)

[Claims] 1. A piezoelectric vibrator whose vibration displacement is excited in a thickness bending vibration mode having three vibration branches in the thickness direction, and a piezoelectric vibrator having electric polarities provided therein and having different electric polarities. The piezoelectric vibrator includes a first electrode, a second electrode, and an electrically neutral third electrode provided on the piezoelectric vibrator, the first electrode and the second electrode being provided on a side surface of the vibrating branch, and the third electrode An electrode structure of a piezoelectric vibrator, characterized in that electrodes are provided on the upper surface and the lower surface of the vibrating branch and are independent from each other.