JPH0141223Y2 - - Google Patents

Description

[Detailed explanation of the invention] (a) Industrial application field The present invention relates to a thickness-shear vibrator that simultaneously excites two thickness-shear vibrations whose displacement directions are orthogonal to each other, and is used in a PLL circuit of a video tape recorder, etc. Used as a resonator for the built-in voltage controlled oscillator.

(b) Prior art A thickness-shear vibrator whose substrate material is a piezoelectric single crystal such as lithium tantalate LiTaO ₃ or lithium niobate LiNbO ₃ can generate two thickness-shear vibrations whose displacement directions are orthogonal to each other and whose electromechanical coupling coefficients are different. It is known that they can be excited at the same time. When this resonator is used as a resonator of a voltage controlled oscillator,
Secondary vibrations with a slightly slower propagation speed that are excited in the direction of a small electromechanical coupling coefficient occur on the low frequency side with respect to the main vibration that is orthogonal to the secondary vibrations, and such secondary vibrations are generated on the low frequency side. This may cause malfunction.

Conventionally, in order to suppress the secondary vibrations that cause the above-mentioned malfunctions, when the board is disc-shaped or rectangular (diamond-shaped), the direction of displacement of the secondary vibrations is made to match the support direction of the board, or In the case of a rectangular shape, a structure has been proposed in which the displacement direction of the main vibration is the long side direction, and the length (width) of the opposing electrode in the short side direction is about 0.8 times or more the length of the short side.

However, in any of these structures, there are various limitations on electrode dimensions, substrate dimensions, etc., and it is difficult to suppress the secondary vibration level to a value that does not pose a problem in actual use, and the variable range of voltage control is difficult. When used as a resonator that requires a wide range of vibrations, there are strict requirements for suppressing the above-mentioned secondary vibrations.

(c) Purpose of the invention The present invention has been devised in view of this point, and its purpose is to suppress secondary vibrations to a value that does not pose a problem in actual use.

(d) Structure of the device The thickness-shear vibrator of the present invention simultaneously excites two thickness-shear vibrations whose displacement directions are orthogonal to each other and have different electromechanical coupling coefficients. The main surfaces are opposed to each other and the short sides are in the direction of the electromechanical coupling coefficient, and one or more grooves are provided along the long sides on at least one of the main surfaces.

(E) Embodiment Figures 1A and 1B are front and side views showing an embodiment of the thickness-shear vibrator of the present invention.
is a rod-shaped substrate made of a piezoelectric single crystal such as LiTaO ₃ or LiNbO ₃ in which thickness-shear vibrations whose displacement directions are orthogonal to each other are simultaneously excited; It has rectangular principal surfaces 2a and 2b that face each other and whose short sides are in the direction of the small electromechanical coupling coefficient, and has strip-shaped main surfaces 2a and 2b that face each other along the long side direction in the vicinity of each boundary in the long side direction of the one main surface 2a. two parallel grooves 3,3
is provided. 4a and 4b are rectangular counter electrodes disposed opposite to each other at the center of the main surfaces 2a and 2b of the substrate 1, and the width W of the counter electrodes 4a and 4b is smaller than the distance D between the two grooves 3 and 3. It is slightly small and is set to be about 80% or more of the short side length l of the main surfaces 2a and 2b, so that it almost covers the short side direction of the main surfaces 2a and 2b. Denoted at 5a and 5b are extraction electrodes extending from the opposing electrodes 4a and 4b toward opposite ends in the long side direction.

When the substrate 1 of the thickness-shear vibrator with such a structure is made of X-cut LiTaO ₃ , the direction θl in which the electromechanical coupling coefficient is large is the direction from +Y axis to +Z as described above.
The range is from 115° to 145° toward the axis, and within this range, the amplitude of the displacement of the main vibration MV is maximum at approximately
126°, and the electromechanical coupling coefficient at that time is approximately
It is 0.443. On the other hand, the direction θs where the electromechanical coupling coefficient is small is in the range of 25° to 55° from the +Y axis to the +Z axis, and within this range, the amplitude of the displacement of the sub-vibration SV is maximum at approximately 36°. The electromechanical coupling coefficient at that time is approximately 0.054.

Therefore, the main vibration MV of the thickness shear vibration excited in the substrate 1 is excited in the direction of the arrow Vl, which is the long side direction of the substrate 1, where the electromechanical coupling coefficient is large, and the secondary vibration SV is the electromechanical coupling coefficient. It is excited in the direction of the arrow Vs, which is the short side direction of the substrate 1 with a smaller value. In the sub-vibration SV whose displacement direction is the short side direction, the opposing electrodes 4a and 4b are on the main surfaces 2a and 2b of the substrate in the short side direction.
Since the sub-vibration SV is almost covered, there is almost no energy trapping effect, and the short side length l of the substrate 1 is sufficiently short compared to the length required to excite the sub-vibration SV, so the amplitude level is reduced. do. Furthermore, due to the two grooves 3, 3 provided on one main surface 2a, the displacement length in the short side direction becomes uneven in the thickness direction, that is, the displacement length on the one main surface 2a side where the grooves 3, 3 are formed. is substantially equal to the interval length D of the grooves, and the displacement length on the other main surface 2b side is equal to the short side length l of the main surface, so that the sub-vibration SV excited in the direction of the displacement length is The Q value decreases, and therefore the amplitude level of the secondary vibration SV is further reduced.

Note that the grooves 3, 3 are formed for the purpose of making the displacement length in the short side direction uneven in the thickness direction, and the shape of the grooves 3, 3 in this embodiment was concave, It is obvious that it may be of a stepped type (not shown).

FIGS. 2 and 3 show the results of measuring the amplitude and phase characteristics of admittance with respect to frequency in a vibrator having the structure of the present invention and a vibrator having a conventional structure.
The common specifications of the samples used for such measurements are as follows.

Γ Substrate 1 Material: Xcut LiTaO ₃ Long side direction: 126° from +Y axis to +Z axis Short side direction: 36° from +Y axis to +Z axis Long side length L: 5 mm Short side length L: 500 μm Thickness t : 200μm Γ Counter electrodes 4a, 4b Material: Silver evaporated film Electrode length a: 1.6mm In addition to the above common specifications, for the resonator of the present invention,
Approximately 30 μm inward in the short side direction from the periphery of one main surface 2a
Two parallel grooves 3, 3 having a width δ of about 20 μm and a depth d of about 30 μm are formed at the position by means of a laser beam, a diamond cutter, or the like.

As is clear from the phase characteristics and amplitude characteristics, it has been experimentally shown that in the vibrator of the present invention, the amplitude of the sub-vibration SV can be reduced, and the phase inversion accompanying the sub-vibration SV can also be improved. It was also confirmed.

In the above embodiment, two grooves 3, 3 were formed on one main surface 2a, but two grooves 3, 3 were formed on the other main surface 2a.
If two grooves are also provided at the corresponding location b, it becomes possible to further suppress the secondary vibration SV. However,
When cutting the wafer into individual rod-shaped substrates 1 by irradiation with a laser beam, the grooves 3, 3 are formed by lowering the energy density of the laser beam or increasing the scanning speed. Therefore, it is more convenient to set the grooves 3, 3 to be located on the same main surface as in this embodiment.

(f) Effect of the invention As is clear from the above explanation, the present invention has one or more grooves along the long side of at least one of the main surfaces whose long sides are in the direction of the large electromechanical coupling coefficient. As a result, the displacement length of the secondary vibrations becomes uneven, and the secondary vibration level can be suppressed to a value that does not pose a problem in actual use. This is especially true for voltage control variables that have strict requirements for suppressing such secondary vibrations. It is useful for use as a resonator that must have a wide width.

[Brief explanation of the drawing]

Figure 1 shows an embodiment of the resonator of the present invention; Figure A is a front view, Figure B is a side view, Figure 2 is a diagram of the amplitude and phase characteristics of the resonator of the present invention versus frequency, and Figure 3 is a diagram of the amplitude and phase characteristics of the resonator of the present invention.
The figure is a diagram showing the amplitude and phase characteristics of a conventional vibrator with respect to frequency. 1...Substrate, 2a, 2b...Main surface, 3...Groove.

Claims (1)

[Scope of utility model registration request] In a thickness-shear vibrator that simultaneously excites two thickness-shear vibrations whose displacement directions are orthogonal to each other and have different electromechanical coupling coefficients, the substrate on which the thickness-shear vibrations are excited simultaneously has a direction of a large electromechanical coupling coefficient. It has main surfaces facing each other with the long side and the short side in the direction of the smaller electromechanical coupling coefficient, and at least one groove is provided along the long side direction on at least one of the main surfaces. Features a thickness-slip oscillator.