JPH0221790Y2 - - 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 at least four chamfers with a width of about 2% to 10% of the short side length are formed along the ridge line in the long side direction. It's in the composition of one of the ridgelines.

(e) Embodiment Figures 1A and 1B are a perspective view and a cross-sectional view of an embodiment of the thickness-shear vibrator of the present invention, in which 1 shows a structure in which thickness-shear vibrations whose displacement directions are orthogonal to each other are simultaneously excited. A rod-shaped substrate made of piezoelectric single crystal such as LiTaO ₃ , LiNbO ₃ , etc. The substrate is a strip whose long side is in the direction of a large electromechanical coupling coefficient and whose short side is orthogonal to the direction of a small electromechanical coupling coefficient. It has main surfaces 2, 2 facing each other in a shape, and
A chamfering process such as beveling is performed along the ridge lines 3, 3, . . . in the long side direction, and slopes 4, 4, . Reference numerals 5 and 5 designate rectangular counter electrodes disposed opposite to each other at the center of the main surfaces 2 and 2 of the substrate 1, and the width W of the counter electrodes 5 and 5 is equal to the short side length a of the main surfaces 2 and 2. It covers the short sides of the main surfaces 2, 2. 6,
Reference numerals 6 denote lead electrodes extending from the opposing electrodes 5, 5 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 displacement of the main vibration MV is maximum at about 126°, and the electromechanical coupling coefficient at that time is about 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 toward the +Z axis, and within this range, the displacement of the secondary vibration SV is maximum at about 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. Since the opposing electrodes 5, 5 cover the main surfaces 2, 2 of the substrate in the short side direction, the sub-vibration SV whose displacement direction is the short side direction has almost no energy trapping effect, and the sub-vibration SV is excited. Since the short side length l of the substrate 1 is sufficiently short compared to the length required for this purpose, the amplitude level is reduced. Furthermore, due to the chamfering process applied to the ridge lines 3, 3... in the long side direction, the displacement lengths in the short side direction become uneven, that is, the displacement lengths on the slopes 4, 4... with the displacement length on the main surface side being the minimum value. Since it increases along the rise, the Q value of the secondary vibration SV excited in the displacement length direction decreases, and therefore,
The amplitude level of the secondary vibration SV is further reduced.

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) : 520μm Thickness (t): 170μm Γ Counter electrode 5, 5 Material: Silver evaporated film Electrode length (d): 1.6mm Electrode width (W): 478μm In addition to the above common specifications, the long side of the resonator of this invention All of the four ridge lines 3, 3, .

As is clear from the phase characteristics and amplitude characteristics, the vibrator of the present invention can reduce the amplitude of the secondary vibration SV that occurs near 10.2MHz, and
It was found that the phase inversion accompanying the secondary vibration SV was also improved. Furthermore, it can be seen that the level of spurious SP present on the high frequency side has also decreased.

Next, the present inventor investigated the relationship between the chamfering process and the level of secondary vibration, and obtained the results shown in FIG. 4. The vertical axis is the secondary vibration level, and the horizontal axis is the short side length l
It is the percentage of the ratio (δ/l) of one chamfer (bevel) width δ to the width δ. Such measurements are made using two resistors R and R connected to the AC signal line Vi as shown in Figure 5.
This was carried out using a circuit in which the vibrator to be measured 10 was connected between them. At each chamfering ratio (δ/l), the level when conduction (through) occurs between the opposing electrodes 5 and 5 is measured using a voltmeter Vo, and using this conduction level as a reference value, the signal source is applied up to the sub-oscillation frequency. As a result of changing the frequency of Vi and comparing the level obtained by the voltmeter Vo with the above conduction level, the curve shown in FIG. 4 was obtained.

When the chamfered resonator of the present invention was mounted in a PLL circuit, malfunctions could be prevented by optimally designing the circuit constants even if −10 dB of secondary vibration occurred at the secondary vibration level shown in Figure 4. . That is, when performing chamfering as in the present invention, the chamfering ratio (δ/
This means that approximately 2% or more is required in terms of l).

On the other hand, the upper limit of the chamfering ratio (δ/l) is that when the chamfering ratio (δ/l) is increased, the secondary vibration level decreases, but the main vibration is reduced as the short side length a of the main surfaces 2, 2 is reduced. A range of up to about 10% is appropriate because it has an adverse effect on the vibration and also saturates the sub-vibration level.

FIG. 6 shows another embodiment of the present invention, in which the substrate 1'
It is characterized by its shape. That is, in the previous embodiment, the substrate 1 has a rectangular parallelepiped shape, and the ridge lines 3,
3... were chamfered, but in this embodiment, the upper and lower surfaces 11, 11 with respect to the main surfaces 2', 2' are wavy, and along the wavy ridgelines 3', 3'... A chamfering process (not shown) is then applied. The above-mentioned corrugated processing can be easily performed by irradiating a beam with sufficiently high energy density, such as an Nd:YAG laser, when cutting out the individual substrates 1' from the wafer. According to such a structure, since the substrate lengths in the short side direction are more irregular, the sub-vibration level can be suppressed more effectively. Therefore, in the case of such a structure, it is sufficient to chamfer one of at least four ridge lines.

(F) Effect of the invention As is clear from the above explanation, the present invention can suppress the sub-vibration level to a value that does not pose a problem in practical use, and is particularly suitable for voltage control, which has strict requirements for suppression of such sub-vibration. It is useful for use as a resonator that requires a wide variable width.

[Brief explanation of the drawing]

1A and 1B are a perspective view and a side view showing an embodiment of the resonator of the present invention, FIG. 2 is a diagram of amplitude and phase characteristics with respect to frequency of a conventional resonator, and FIG. 3 is a diagram of the resonator of the present invention. Fig. 4 is a curve diagram obtained as a result of measuring the relationship between chamfer ratio and sub-vibration level, Fig. 5 is a diagram of such a measurement circuit, and Fig. 6 is a diagram of the vibrator of the present invention. FIG. 7 shows perspective views for explaining other embodiments. 1, 1'...Substrate, 2, 2'...Main surface, 3, 3'
...Ridge, 4...Slope.

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. The main surfaces are opposed to each other, with the long side being the short side and the direction of the small electromechanical coupling coefficient being the short side, and a chamfer with a width of about 2% to 10% of the short side length along the ridge line in the long side direction. A thickness-shear vibrator characterized in that processing is applied to at least one of four ridge lines.