JPH0685598A - Crystal oscillator for sc cut - Google Patents

Abstract

PURPOSE:To provide the third-order overtone SC cut crystal oscillator which can suppress oscillation in the B mode and A mode of sub oscillation and can surely excite oscillation in the C mode of main oscillation. CONSTITUTION:Concerning the disk-shaped SC cut crystal oscillator which is resonated with the third-order overtone cut out of a face rotating the face of crystal orthogonal to a Y axis almost at 33 deg. with an X axis as a center and further rotating it almost at 22 deg. from this rotated position with a Z axis as a center, the diameter of a crystal piece 1 is longer than 3mm and shorter than 20mm, one plate face of the crystal piece 1 is made flat, convex work is applied to the other plate face, the circular exciting electrode of a diameter shorter than the 30% diameter of the crystal piece 1 is formed in counter to both of side plate faces of the crystal piece 1, and the center of this exciting electrode is positioned in the range of + or -10 deg. from the center of the crystal piece 1 in the direction of an XX' axis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an SC-cut crystal unit used in a third overtone, and more particularly to suppression of side vibration.

[0002]

2. Description of the Related Art Generally, a piezoelectric crystal can excite piezoelectric vibration only at a specific cutting angle with respect to a crystal axis. For example, even in the case of a crystal resonator that utilizes the piezoelectric characteristics of crystal, piezoelectric vibration can be excited only at a specific cutting angle with respect to the crystal axis, and there are a plurality of combinations of these cutting angles, and It exhibits unique vibration characteristics at the cutting angle of. For example, an AT-cut crystal resonator most commonly used at a frequency of several MHz to ten and several MHz exhibits a cubic curve-shaped temperature characteristic having an inflection point near 25 ° C. On the other hand, recently, SC-cut crystal resonators having excellent performances such as stress sensitivity, thermal shock characteristics, and phase noise performance have attracted attention. Such an SC-cut crystal resonator exhibits a cubic curve-shaped temperature characteristic having an inflection point near 95 ° C. Therefore, it has extremely desirable characteristics for use in a so-called constant temperature oven type oscillator having a high frequency stability, which is stored in a constant temperature oven heated to a constant temperature for use.

By the way, such an SC-cut crystal oscillator has a B-mode (shown in the figure) in the vicinity of the C-mode resonance (shown in the figure), which is the main vibration, and at a frequency on the high frequency side, as shown in FIG. B) and A mode (shown in A) side vibrations are generated. Here, since the value of the equivalent resistance of vibration in the A mode (hereinafter abbreviated as CI) is generally larger than that in the C mode, there is no particular problem. On the other hand, the CI of the B mode vibration is equal to or smaller than that of the C mode in some cases. Therefore, when an oscillator is actually manufactured, there is a problem that the oscillator often oscillates in the B mode which is a secondary vibration. Therefore, in the case of using the SC-cut crystal oscillator, it is necessary to suppress the B-mode vibration and make its CI larger than that of the C-mode in order to reliably excite the C-mode vibration. . For this reason, B-mode vibrations have been suppressed by variously devising the outer shape of the crystal piece, the holding position, and the like. In such a device, for example, the B-mode vibration is suppressed by performing so-called beveling in which both side plate surfaces of the crystal blank are formed into a convex lens shape so as to be asymmetrical. However, in such a case, there has been a problem that the outer shape of the crystal piece has to be made into a special shape, the processing is troublesome, and the productivity is low.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and suppresses auxiliary vibrations of A mode and B mode and surely excites vibration of C mode which is a main vibration. It is an object of the present invention to provide an SC-cut crystal resonator used in the third overtone, which does not require fine adjustment and has good productivity.

[0005]

According to the present invention, a plane perpendicular to the Y axis of a crystal of quartz is rotated about the X axis by about 33 °,
Furthermore, in the disk-shaped SC-cut crystal resonator that resonates with a third overtone cut out from the surface rotated about 22 degrees from the rotated position about the Z axis, the diameter of the crystal piece is larger than 3 mm and 20 mm. Smaller than that, one plate surface of the crystal piece is a flat surface, and the other plate surface is subjected to convex processing.
A circular excitation electrode having a diameter smaller than 0% is formed, and the center of the excitation electrode is located within a range of ± 10 ° from the center of the crystal element with respect to the XX 'axis direction. .

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the plan view of the plate surface of the crystal piece shown in FIG. 1 and the sectional view of the crystal piece shown in FIG. In the figure, 1 is an SC-cut crystal piece having a diameter of 14 mm. The crystal piece 1 was cut from a surface rotated about 22 ° about the Z axis from the rotated position about 33 ° about the X axis on the surface orthogonal to the Y axis of the crystal of the crystal. It is a thing. And the rotated X axis and Z
The axes were taken as the XX ′ axis and the ZZ ′ axis, respectively, and the end portion in the + XX ′ axis direction was cut in parallel with the ZZ ′ axis, and the dimension in the XX ′ axis direction was set to 13.5 mm. Further, as shown in the cross-sectional view of FIG. 2, the crystal piece 1 has one plate surface as a flat surface and the other plate surface is subjected to convex processing to generate an unnecessary vibration mode.
I try to suppress spurious. Then, a circular electrode having a diameter of 5 mm is formed on both sides of the crystal blank 1 so as to face each other. The center of this excitation electrode is the crystal piece 1.
It is provided so as to be eccentric in the XX'-axis direction from the center. The excitation electrode is formed by depositing Cr (chrome), which has good adhesion to quartz, as a first layer, and then depositing Au (gold), which is a good conductor of electricity and is chemically stable, as a second layer. is there. The thickness of these electrode materials was such that Cr was about 200 m-10 and Au was about 1500 m-10. With this configuration, for example, as shown in the figure, the B-mode resonance characteristic can be sufficiently suppressed with respect to the C-mode resonance characteristic, and the C-mode resonance, which is the main vibration, can be reliably excited. .

In the present invention, the diameter of the crystal piece is 3 mm.
Or 20 mm. The reason is that it is difficult to obtain a desired resonance characteristic with a diameter smaller than 3 mm.
This is because a diameter larger than mm is too large and there is a problem in practicality. The excitation electrode is circular and 30% of the diameter of the crystal piece.
This is because the diameter of the excitation electrode is large, or unnecessary vibration modes are likely to occur when the diameter of the excitation electrode is not circular. Further, the reason why the excitation electrode is eccentric in the XX'-axis direction is that when the excitation electrode is formed at different positions on the XX'-axis passing through the center of the crystal element, the C mode, B
The level of each of the C-mode, the A-mode and the A-mode is measured, and similarly, the level of each of the C-mode, the B-mode and the A-mode is measured when electrodes are formed at different positions on the ZZ 'axis passing through the center of the crystal piece. did. As a result of these measurements, the level difference (dB) between the B mode and the A mode when the level of the C mode was used as a reference was as shown in the graph of FIG. In FIG. 3, the horizontal axis is the distance from the center of the crystal element to the center of the excitation electrode, is the electrode moved in the −Z direction, is the electrode moved in the + Z direction, is the electrode moved in the −X direction, Is moved in the + X direction. From the results shown in FIG. 3, in order to reduce the levels of the B mode and the A mode, which are the sub-vibrations, with respect to the level of the C mode, which is the main vibration, the position of the electrode is more than that of the center of the crystal piece. It is desirable to make it eccentric in the + XX ′ axis direction, and in this case, for example, in the XX ′ axis direction.2.
When the eccentricity is 5 mm, the B-mode resonance is lowered by about 9 dB, which means that it can be sufficiently suppressed. With such a configuration, the position where the excitation electrode is formed may be decentered in the XX'-axis direction. Therefore, for example, by using a vapor deposition mask in which the electrode position is decentered in advance, it is possible to easily obtain a crystal vibration having a good resonance characteristic. Since the child can be mass-produced, there is no need to make fine adjustments and variations in characteristics can be reduced.

As described above in detail, according to the present invention, A
It is possible to provide an SC-cut crystal resonator used in the third overtone, which can suppress the secondary vibrations of the mode and the B mode without fail and excite the vibration of the C mode, which is the main vibration.

[0009]

[Brief description of drawings]

FIG. 1 is a plan view of a plate surface of a crystal piece according to an embodiment of the present invention.

2 is a side view of the crystal piece shown in FIG. 1. FIG.

FIG. 3 is a graph showing the amount of eccentricity of the electrodes of the crystal unit of the present invention and the level difference between B mode and C mode level.

FIG. 4 is a diagram showing a resonance characteristic of a crystal unit according to an embodiment of the present invention.

[Explanation of symbols]

 1 crystal piece

Claims (1)

[Claims] 1. A plane perpendicular to the Y-axis of a crystal of quartz is rotated about 33 ° about the X-axis, and further cut out from this rotated position about 22 ° about the Z-axis.
In a disk-shaped SC-cut crystal resonator that resonates with the next overtone, the diameter of the crystal piece is larger than 3 mm and smaller than 20 mm, and one plate surface of the crystal piece is flat and the other plate is convex-processed. Then, a circular excitation electrode having a diameter smaller than 30% of the diameter of the crystal piece is formed so as to face both sides of the crystal piece, and the center of the excitation electrode is set in the XX'-axis direction from the center of the crystal piece. S characterized by being positioned within ± 10 °
C-cut crystal unit