JPS59107619A - Tantalic acid lithium oscillator - Google Patents

Abstract

PURPOSE:To form a tantalic acid lithium oscillator with high accuracy by turning clockwise the long side for a prescribed angle from the Y axis within the Y-Z plane, and bringing the ratio of the long side to the short side of the major plane to a prescribed value or over. CONSTITUTION:The secondary oscillation is suppressed sufficiently, furthermore the oscillator with small size and a low CI value is obtained by bringing the ratio of the long side to the short side to >=2, in a rectangular oscillator where the long side of the major plane of an X-cut plate of the oscillator 1 is turned clockwise by 43 deg. or 63 deg. from the Y axis. Thus, the oscillator is miniaturized, the CI value is decreased and the spurious component due to the secondary oscillation is suppressed remarkably.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lithium tantalate vibrator using piezoelectric lithium tantalate.

In general, piezoelectric elements such as lithium tantalate (LiTaO2) and lithium niobate (LINb03) have a large electromechanical coupling coefficient, so they are useful as piezoelectric materials for broadband filters and wide variable width voltage-controlled oscillators. In particular, attempts are being made to put thickness-shear resonators using lithium tantalate into practical use because they are easy to process and have relatively good temperature characteristics. However, in such a vibrator using lithium tantalate, the displacement directions are perpendicular to each other, and two thickness shear vibrations having different electromechanical coupling coefficients are simultaneously excited. For this reason, if one vibration is the main vibration, the other vibration exists as a sub-vibration, which causes various problems.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a high-performance lithium tantalate oscillator that can significantly suppress the snorious component due to secondary vibrations with a simple configuration, is small in size, and has high performance. That is.

An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a plan view, and numeral 1 indicates a vibrator made of lithium tantalate. This resonator is made by molding a plate into a rectangular shape having a main surface cut out along the y and z planes perpendicular to the mutually orthogonal crystal axes of lithium tantalate, and the x, y, and zOX axes, and is not shown on the plate surface. Electrodes are formed and a high frequency signal is applied thereto to excite thickness shear vibration. The wood loop equation for the X-plate of lithium tantalate is given as follows.

It is the stiffness that is expressed as a stiffness, and it is possible to find three C as solutions. However, one of the solutions is not piezoelectrically excited, and the remaining two solutions are found to be piezoelectrically excitationable. Also, these two solutions are the vibration vl of a transverse wave with a high speed of sound.

Slow transverse wave vibration V! It is. Generally, the X-electrode of lithium tantalate uses the fast transverse wave vibration vl as the main vibration, but at the same time the slow transverse wave vibration V! The secondary vibration caused by this causes syspulus.

Therefore, in a disc-shaped, square-shaped oscillator, etc., the main vibration v
Sub-vibration V for 1! are excited to approximately the same level. Therefore, by forming the main surface into a rectangular shape elongated in the direction of the main vibration v1 as shown in Fig. 1, it is possible to suppress the level of the sub-vibration V, as shown in the frequency response characteristic diagram shown in Fig. 2, for example. can. Here, the level difference between the main vibration V and the sub-vibration v2 changed as shown in FIG. 3 with respect to the rotation angle θ when the long side of the main surface of the vibrator was rotated clockwise from the Y axis.

As is clear from this result, the maximum level difference is 20
dB and a rotation angle θ=53°. Also, if the above level difference is allowed at 19 dB, the rotation angle θ = 53° ±
The angle may be 4°, that is, 49° to 57°. Furthermore, if the level difference is 17 dB, the rotation angle θ = 53°±
The angle may be 10°, that is, 43° to 63°. Further, for an X plate whose long side is rotated 50° clockwise from the Y axis and whose width is 1.5 cm and thickness is approximately 0.7 cm, the relationship between the length t of the long side and the cr value is as shown in Figure 4. became. Note that the resonant frequency of the above vibrator is 3.5 MHz. As is clear from this result, by making the length of the long side t twice as long as the width, the ficI value becomes a constant low value.

Therefore, in a rectangular vibrator in which the long side of the main surface of the X plate of lithium quantalate is rotated 43° to 63° clockwise from the Y axis, the ratio of the long side to the short side is made to be at least twice as large. It is possible to obtain a vibrator which can sufficiently suppress secondary vibrations, is small in size, and has a low CI value.

As detailed above, the present invention provides lithium tantalate with
Form the board into a rectangle, and the long side is Y.

It is rotated 43° to 63° clockwise from the Y-axis within 2,000 planes, and the ratio of the long side to the short side of the main surface is more than double, which greatly suppresses the snorious component due to secondary vibration. However, it is possible to provide a lithium tantalate oscillator that is small in size and has a low CI value.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an embodiment of the present invention, FIG. 2 is a diagram showing frequency response characteristics of a lithium tantalate oscillator, and FIG.
The figure shows the relationship between the rotation angle of the long side from the Y axis and the attenuation amount of Sgelius, and Figure 5-4 shows the relationship between the CI value and the ratio of the long side to the short side. Applicant's agent Patent attorney Takehiko Suzue 6-

Claims (1)

[Claims] It is formed into a rectangular shape with the main surface along the Y, z plane perpendicular to the X axis of the crystal axis of lithium tantalate, and the long side is 43° clockwise from the Y axis in the Y, z plane. A lithium tantalate oscillator characterized by being rotated by 63 degrees and having a ratio of the long side to the short side of the main surface which is more than double.