JPS6357967B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a high-coupling piezoelectric vibrator using an X-plate of LiTaO ₃ .

(b) Background of the technology When a suitable electrode is formed on a piezoelectric material such as quartz crystal or LiTaO ₃ and an alternating current electric field is applied to the electrode, the piezoelectric material generates stress with a frequency equal to the applied electric field, and the frequency of the applied electric field increases. When it matches the natural frequency of the piezoelectric material, it resonates and produces strong vibrations. Since such vibrators are small and have high performance, they are widely used as oscillation circuits and filters in communication devices and the like.

(c) Prior art and problems Figure 1 is a diagram for explaining a piezoelectric strip type thickness-shear oscillator using a single crystal of LiTaO ₃ as the piezoelectric material. shows a diagram explaining the magnitude of vibration. In addition, the reference numeral 1 in the figure is a vibrating element cut out from a single crystal X plate of LiTaO ₃ , 2 and 2' are electrodes formed oppositely on the opposing main surfaces of the vibrating element 1, respectively.
X, Y, and Z are crystal axes;

In Fig. 1, the vibrating element 1 is cut out into a strip with a rectangular cross section from an X plate with a surface perpendicular to the crystal X axis, and the Y' and Z' axes are clockwise with respect to the Y and Z axes, respectively. It is at an angle of 50° ± 2° to
Opposing electrodes 2 and 2' are patterned over the entire width of the main surface of the element perpendicular to the X-axis. When an alternating current electric field is applied to the electrodes 2 and 2', the element 1 generates thickness shear vibration in the direction of the arrow shown in Fig. 2. The magnitude of the vibration is greatest at the center and decreases toward both ends as shown in Fig. C.

This type of vibrating element 1 has the effect that by setting the longitudinal direction (length L) at an angle of -50°±2° with respect to the Y axis of the crystal, spurious noise is reduced and high quality performance can be obtained. have However, when the length L, width W, and thickness H of the element 1 are freely selected, spurious waves occur in the frequency characteristics and a decrease in the mechanical quality factor Q is observed, which has been viewed as a problem.

(d) Object of the Invention In view of the above-mentioned conventional problems, an object of the present invention is to provide a high-coupling piezoelectric vibrator free of spurious components.

(e) Structure of the Invention The above object is to create a strip-shaped body using an X-plate of LiTaO ₃ single crystal, with a rectangular cross section and whose longitudinal direction is 50°±2° clockwise from the Y-axis in the X-plane of the crystal. In a piezoelectric strip type vibrator which uses a vibrating element as a vibrating element, electrodes are formed over the entire width on opposite principal surfaces parallel to the crystal X plane of the vibrating element, and performs thickness shear vibration,
The vibrating element is characterized in that L/H is 14 or more, where the length of the main surface in the longitudinal direction is L, the width of the main surface in the direction perpendicular to the longitudinal direction is W, and the thickness in the X-axis direction is H. Achieved by piezoelectric vibrators.

(f) Embodiments of the Invention The present invention will be described below using characteristic diagrams of a piezoelectric vibrator according to the present invention.

Figure 2 shows the experimentally determined values of the mechanical quality factor Q when the ratio L/H between the length L of the main longitudinal surface and the thickness H of the LiTaO ₃ vibrating element shown in Figure 1 is changed. FIG.

In Figure 2, L/H is plotted on the horizontal axis and Q is plotted on the vertical axis. Curve A shows the relationship between L/H and Q. In the range of L/H > 14, Q is Although it is constant, Q rapidly decreases when L/H<14.
Therefore, when L/H>14, a constant Q value is ensured.

FIG. 3 is a perspective view for explaining the vibration mode of the LiTaO ₃ vibration element shown in FIG. 1, FIG. 4 is a diagram showing an example of the frequency characteristic of the element, and FIG. 5 is an example of the admittance characteristic of the element. FIG.

In FIG. 3, the vibrating element 1 applies a predetermined electric field to the electrode 2 and the electrode 2' (not shown) to generate a thickness shear vibration mode M, which is the main vibration, and a width shear vibration mode that adversely affects the element characteristics. m is generated, and the frequency of the vibration mode m determined by the width W of the main surface of the element 1 moves toward the lower frequency side as the width W increases.

In Figure 4, the horizontal axis represents frequency (MHz), the vertical axis represents response level (dB), and curve B
shows an example of the frequency characteristics of the vibrating element.
The peak P ₁ of the curve B indicates the resonance response level of the thickness shear vibration mode M, and the peak P ₂ is a spurious generated when the width shear vibration mode m overlaps with the vibration mode M, and this spurious is the resonance point peak. If P is close to ₁ , it will have a negative effect on the characteristics of the resonator.

In Fig. 5, the horizontal axis represents frequency and the vertical axis represents admittance. Curve C shows an example of the admittance characteristic of the vibrating element, and point _r on the horizontal axis
indicates the position of the resonant frequency, and point _a indicates the position of the anti-resonant frequency. In a resonator having such a curve C, if there is the above-mentioned spurious in the vicinity of _r , its oscillation frequency will become extremely unstable.
Design consideration is required to keep spurious components sufficiently away from _r .

FIG. 6 is a diagram illustrating the frequency constant k·H at which spurious waves occur due to width shear vibration by mode, based on experiments when the ratio W/H between the main surface width W and the thickness H of the vibrating element is changed.

In Fig. 6, W/H is plotted on the horizontal axis, and H (Hz/m) is plotted on the vertical axis, and curves D and E connect spurious generation points for each of the first, third, and fifth width shear vibration modes. , F. and,
The ・H level of the resonant frequency (approximately 1950Hz・m) is indicated by the dotted _line
2170Hz・m) is shown by the dashed-dotted line _a , and the normal lower limit/H level (approximately 1700Hz・m), which is adversely affected when spurious occurs, is shown by the dashed-dotted line _b .
The area of W/H where spurious does not occur is curve D
W/H is approximately 1.35 at the intersection of the two-dot chain line _b and the curve E
A first region G ₁ where W/H is about 3 at the intersection of the curve E and the dashed-dotted line _a , and W/H is about 3.8 at the intersection of the curve E and the dashed-dotted line _b , and the curve F and the dashed-dotted line The intersection point of _a becomes a second region _G2 where W/H is about 5.

(g) Effect of the invention As explained above, the piezoelectric vibrator of the present invention defines the ratio between the longitudinal length of the main surface of the element and the thickness of the element,
Furthermore, by specifying the ratio between the width of the main surface of the element and the thickness of the element, spurious noise is reduced and high quality is achieved.
The effect of obtaining a highly reliable resonator is significant.

[Brief explanation of drawings]

Figure 1 is a diagram for explaining a piezoelectric strip type thickness-shear vibrator, and Figure 2 is a diagram similar to that shown in Figure 1.
A diagram showing the mechanical quality factor Q characteristics when changing the ratio L/H of the main surface length and thickness of the LiTa ₂ O ₃ resonator element,
FIG. 3 is a diagram for explaining the vibration mode of the vibration element, FIG. 4 is a diagram showing an example of the frequency characteristic of the vibration element, FIG. 5 is a diagram showing an example of the admittance characteristic of the vibration element, and FIG. is the main surface width W of the vibrating element
FIG. 4 is a diagram showing the spurious generation frequency constant characteristics when the ratio W/H between the thickness H and the thickness H is changed. In the figure, 1 is the vibrating element, 2 and 2' are the electrodes, L is the length in the longitudinal direction of the main surface of the element, H is the width of the main surface of the element, W is the thickness of the element, and X, Y, and Z are simple. The crystal axes, Y' and Z', indicate the axes of the main surface of the element.

Claims (1)

[Claims] 1. A vibrating element is a strip-shaped body using an X plate of LiTaO ₃ single crystal and having a rectangular cross section and whose longitudinal direction is 50°±2° clockwise from the Y axis in the X plane of the crystal. In a piezoelectric strip type vibrator that performs thickness-shear vibration in which electrodes are formed over the entire width on opposing principal surfaces parallel to the crystal A piezoelectric vibrator characterized in that L/H is 14 or more, where W is the main surface width in the direction perpendicular to the direction, and H is the thickness in the X-axis direction. (1) The above vibration elements have a W/H of 1.35~3.0 and 3.8~
5.0. The piezoelectric vibrator as set forth in claim 1 above.