JPS6340492B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a piezoelectric vibrator that performs thickness-shear vibration. A piezoelectric resonator such as a crystal resonator generally has many sub-vibrations in addition to the main vibration. As an example, a planoconvex structure with thickness-shear vibration
AT-cut crystal resonators have a main oscillation frequency of
Those around 4.2MHz are around 4.6MHz and 4.7MHz
There is secondary vibration nearby. When measuring the surface charge distribution using an electric probe method, these main vibrations and sub-vibrations are found to be the first, third, and third vibrations.
A charge concentration region as shown in Fig. 5 and charge distribution curves as shown in Figs. 2, 4, and 6 are shown. Figure 1 shows main vibration 1
FIG. 2 shows a charge distribution curve of the main vibration 1 on the Z-axis. From FIGS. 1 and 2, it can be seen that in the main vibration 1, the charges are concentrated in the central region 1a. Figure 3 shows charge concentration regions 2a, 2b, 2c of secondary vibration 2.
, and FIG. 4 shows the charge distribution curve on the Z-axis of the secondary vibration 2. From Figures 3 and 4, it can be seen that in secondary vibration 2, charges are concentrated in the central region 2a, and charges with different polarities are concentrated in regions 2b and 2c on both sides of the region 2a on the Z axis. Recognize. In addition, Fig. 5 shows the charge concentration region 3 of other sub-vibration 3.
a, 3b, and 3c, and FIG. 6 shows the charge distribution curve on the X-axis of the sub-oscillation 3. 5 and 6, in sub-vibration 3, charges are concentrated in the central region 3a, and charges with different polarities are concentrated in the region 3a.
It can be seen that they are concentrated in regions 3b and 3c on both sides of the X-axis of a. If the oscillation frequency of the main vibration and the oscillation frequency of the sub-vibration are close to each other, the crystal resonator may oscillate due to the sub-vibration, or the main vibration may be influenced by the sub-vibration. Also, Figures 7 and 8 show other conventional examples, and although this conventional crystal resonator was effective in suppressing one sub-vibration, it was not effective in suppressing other sub-vibrations. It was small. It is an object of the present invention to provide a thickness-shear piezoelectric vibrator having a drive electrode that can efficiently drive the main vibration and suppress a plurality of other sub-vibrations. Another object of the present invention is to improve the Q value of a piezoelectric vibrator. An embodiment of the present invention will be described in detail below based on the drawings. In FIGS. 9 and 10, 4 is a crystal resonator which is a piezoelectric vibrator, and a crystal piece 5 which is a piezoelectric element,
Drive electrodes 6 and 7 provided on opposing surfaces of this crystal piece
It consists of. Although the crystal piece 5 has a disc shape, it is not limited to this, but may have a bebesung shape, a planoconvex shape, or a planoconvex shape.
It may be biconvex-shaped. Drive electrodes 6 and 7 are formed on opposing surfaces of the crystal blank 5 by vacuum evaporation or the like, and these drive electrodes extend in the outer circumferential direction and include extraction electrodes 6a and 7a formed at the same time. Holding members (not shown) for the crystal piece 5 are fixed to the outer peripheries of the extraction electrodes 6a, 7a, and a voltage is applied to the drive electrodes 6, 7 from these holding members. One of the drive electrodes 6 is provided with a central through hole 8 in the center and two symmetrical through holes 9, 1.
0 is set. First, to explain the central through hole 8 in detail, the central through hole 8 has a narrow center in the X-axis direction.
_W2 , and both sides of the center on the Z-axis are wide _W1 in the X-axis direction. The narrow central part corresponds to the charge concentrated region 1a of the main vibration 1 shown in the first diagram, and the wide side parts correspond to the three regions 2 where the charges of the sub vibration 2 shown in the third diagram are concentrated.
Two areas 2b, 2 on both sides of a, 2b, 2c
It corresponds to c. Note that the charge concentration region is, in other words, a region where vibration energy is large. As shown in FIG. 9, the right part of the central through hole 8 is a deleted part 8a where a part of the drive electrode 6 is deleted.
The central through hole 8 is opened by a removed portion 8a. This removed portion 8a corresponds to a support member of a mask that forms the central hole 8 when forming the drive electrode 6 on the crystal piece 5 by vacuum deposition or the like. Therefore, if the mask can be supported by an appropriate method, the removed portion 8a is not necessary. Next, the symmetrical through holes 9 and 10 will be explained in detail. These two symmetrical through holes are symmetrical about the Z axis and are located on the X axis. These symmetrical holes 9, 10 correspond to two regions 3b, 3c on both sides of the three regions 3a, 3b, 3c shown in FIG. 5 where the charges of the other sub-vibration 3 are concentrated. As shown in FIG. 9, the upper part of the symmetrical through hole 9 and the lower part of the symmetrical through hole 10 are connected to the driving electrode
The symmetrical through hole 9 is opened upward by the deleted part 9a, and the symmetrical through hole 10 is opened downward by the deleted part 10a. Similar to the removed portion 8a, these removed portions 9a and 10 also correspond to support members for a mask that forms symmetrical through holes 9 and 10 when forming the drive electrode 6 on the crystal piece 5 by vacuum deposition or the like.
Therefore, the deleted portions 9a, 10a are not necessarily necessary, and the symmetrical through holes 9, 10 can be made circular at least similar to the regions 3b, 3c described above. Drive electrode 6 between central through hole 8 and symmetrical through holes 9 and 10
The arched portions 6a and 6c are electrodes that, together with the drive electrode 7, efficiently drive this crystal resonator with its main vibration. When a voltage is applied to the drive electrodes 6 and 7 of this crystal resonator, this crystal resonator 4 is efficiently driven by the main vibration 1 and is hardly driven by the sub vibrations 2 and 3. And it is hardly affected by secondary vibrations 2 and 3. Further, since one drive electrode 6 of this crystal resonator 4 does not have an electrode film at the center of the crystal piece 5 where the vibration displacement is large, the fluctuation in the oscillation frequency of this crystal resonator due to aging is extremely small. Furthermore, since the other drive electrode 7 of this crystal oscillator has an electrode film at the center of the crystal piece 5 which has a large vibrational displacement, the oscillation frequency of this crystal oscillator can be efficiently adjusted by the added mass. Next, another embodiment of the present invention will be described based on FIG. The crystal resonator 14 includes a crystal piece 15 and a crystal piece 15.
A drive electrode (not shown) similar to that shown in FIG. 9 provided on one surface of the drive electrode 1 provided on the other surface of the
It consists of 7. The drive electrode 17 has three regions 3 lined up on the X-axis where charges of other sub-oscillations 3 are concentrated.
Two areas 3b, 3 on both sides of a, 3b, 3c
The upper and lower ends are removed in parallel to the Z-axis direction to avoid c, making it elongated. Therefore, compared to the crystal resonator 4 of the embodiment described above, this crystal resonator 14 is less susceptible to the influence of other sub-oscillations 3. Further, another embodiment of the present invention will be described based on FIG. 12. The crystal resonator 24 includes a crystal piece 25, a drive electrode (not shown) similar to that shown in FIG. 9 provided on one side of the crystal piece, and a drive electrode 2 provided on the other side of the crystal piece.
It consists of 7. The drive electrode 27 is provided with two opposing through holes 28, 29, which are opposed to the symmetrical through holes 9, 10 shown in FIG. That is, the opposing through holes 28 and 29 are located in two regions 3b on both sides of the three regions 3a, 3b, and 3c lined up on the X-axis where the charges of other sub-oscillations 3 are concentrated on the other surface of the crystal piece 25. , 3c. Therefore, this crystal oscillator 24 is also the same as the crystal oscillator 4 of the above embodiment.
Compared to this, it is less susceptible to the influence of this sub-vibration 3. Here, regarding the conventional crystal resonator shown in the seventh and eighth figures, the crystal resonator 4 shown in the ninth and tenth figures, the crystal resonator 14 shown in the eleventh figure, and the crystal resonator 24 shown in the twelfth figure, the main vibration 1, the sub-vibration 2. Experimental data of crystal impedance R ₁ , R ₂ , R ₃ in sub-vibration 3 and Q value in main vibration 1 are shown in the table below.

[Table] In this table, when compared with the conventional crystal resonators, it can be seen that the crystal resonators 4, 14, and 24 of the present invention were able to achieve an improvement in the Q value. This is because the crystal impedance R ₁ in the main vibration 1 is reduced. Also, crystal oscillators 14, 24
It can be seen that the crystal impedance R ₃ in the other sub-oscillation 3 has increased significantly. For this reason, the crystal oscillators 14 and 24 are more difficult to be driven by the other sub-oscillations 3, but the Q value is slightly reduced. As described above, the thickness-shear piezoelectric vibrator of the present invention can be efficiently driven by the main vibration, and is difficult to be driven by the plurality of sub-vibrations. For this reason, the Q value of the main vibration can be improved, making it less susceptible to the influence of secondary vibrations.

[Brief explanation of the drawing]

Figure 1 is a front view of a conventional AT-cut crystal resonator showing the surface charge distribution in the main vibration;
The figure is a surface charge distribution curve on the Z-axis in Figure 1. Figure 3 is a front view of a conventional AT cut crystal resonator showing the surface charge distribution in sub-vibration. Figure 4 is the Z-axis in Figure 3. Above surface charge distribution curve diagram,
Figure 5 is a front view of a conventional AT-cut crystal resonator showing the surface charge distribution in other sub-oscillations, Figure 6 is a surface charge distribution curve on the X axis in Figure 5, and Figures 7 and 8. 9 is a front view and a rear view of another conventional example, FIG. 9 is a front view of an embodiment of the present invention, and FIG. 10 is a front view of another conventional example.
11 is a rear view of another embodiment of the present invention, and FIG. 12 is a rear view of still another embodiment. 4, 14, 24...Crystal resonator, 5, 15, 2
5... Crystal piece, 6... One drive electrode, 7,1
7, 27...Other drive electrode, 8...Central through hole,
9, 10... Symmetrical through holes, 28, 29... Opposing through holes.

Claims (1)

[Claims] 1 Drive electrodes are provided on opposing surfaces of a piezoelectric element that performs thickness shear vibration, one of the drive electrodes has a central through hole and two symmetrical through holes, and the central through hole has a central through hole. The area is narrow in the X-axis direction, and this central area corresponds to the area where the charges of the main vibration are concentrated, and the Z
Both sides of the central part on the axis are wide in the X-axis direction, and these both sides are located in two areas on both sides of the three areas lined up on the Z-axis where charges of sub-vibration are concentrated. The above two symmetrical holes are symmetrical with respect to the Z-axis and located on the X-axis, and among the three regions lined up on the X-axis where charges of other sub-vibrations are concentrated. A thickness-slip piezoelectric vibrator characterized in that it corresponds to two regions on both sides of the oscillator. 2 In claim 1, the other drive electrode is arranged along the Z-axis so as to avoid two regions on both sides of the three regions arranged on the X-axis where charges of other sub-oscillations are concentrated. A thickness-shear piezoelectric vibrator characterized by being elongated in the direction. 3. The thickness-shear piezoelectric vibrator according to claim 1, wherein the other drive electrode has two symmetrical through-holes and two opposing through-holes facing each other.