JPS5945243B2 - Crystal oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a bending vibration type rod-shaped crystal resonator formed from a thin crystal plate.

The purpose of the invention is to have a small size, low impedance level,
Another object of the present invention is to provide a crystal resonator that is easy to manufacture.

A rod-shaped crystal oscillator that performs bending vibration is small, has a high Q value, and is highly stable, so it is widely used as a reference oscillator for electronic wristwatches.

Traditionally, such transducers have been processed using mechanical methods such as wire saws, diamond wheel cutters, and ultrasonic processing, but recently, in order to improve productivity and downsize, the thickness of the transducer has been reduced. Chemical methods using photoetching techniques have been used.

However, the electrical performance of such a thin vibrator is inferior to that of a thick vibrator processed by a mechanical method due to its high CI (crystal impedance).

FIG. 1 is a perspective view showing an example of a rod-shaped crystal resonator processed by a conventional mechanical method, and FIG. 2 is a cross-sectional view taken along the line II in FIG. 1.

In the figure, X, Y, and Z are the crystal axes of the crystal, and 1 in the figure is the axis of x, y that is perpendicular to each other by rotating the Y-axis and Z-axis by α, that is, 0 to +8 degrees, around the X-axis of the crystal. This is a rod-shaped crystal piece made of a known rotating X plate cut out along the 'z' direction.

The coordinate axes and angles are determined by Issaku Koga, "Unification of representation methods and symbols for crystal piezoelectricity," published in August 1930, Journal of the Institute of Electrical Engineers of Japan, Vol. 58, No. 601, p. 657.
It is based on page 659.

And 2a is the side electrode of the rod-shaped crystal piece 1, 3a
1 is an electrode formed on the main surface of a rod-shaped crystal piece 1, and piezoelectric vibration is excited by applying a high frequency voltage between these electrodes 2a and 3a.

That is, the pattern of the electric field in a certain half period is as shown in FIG. 2, and this X-direction component induces strain in the X-axis force direction in the crystal.

As is clear from the polarity, the strain in the direction of the X-axis force is, as shown in the figure, with the center line of the rod-shaped crystal piece as the boundary, if the left side is ■, the right side is in reverse phase with e, and the desired bending is achieved. Vibration is excited.

The resonant frequency of a rod-shaped bent crystal resonator is determined mainly by the length in the X-axis force direction and the width in the X-axis force direction, and is hardly related to the thickness in the Z-axis direction.

Therefore, in terms of the required frequency, the thickness can be made very thin, and with such thin thicknesses, it is possible to cut out many rod-shaped blanks of the same shape from a large blank plate at once by photo-etching. It is now possible.

Further, the electrodes 2a to be formed on the side surfaces can be easily formed by cutting out a bar-shaped blank and then depositing the electrodes on the blank individually or by stacking several electrodes.

However, in such a thin vibrator, if a conventional electrode shape is used, the CI becomes extremely high, making it difficult to use.

The reason for this is that, as shown in Figure 3, the electric field is concentrated at the four corners, and as will be described later, the lines of electric force hardly pass through areas where the strain is sufficiently large, making it impossible to perform effective piezoelectric excitation.

The present invention has been made in view of these circumstances, and it is an object of the present invention to provide a vibrator that is thin and has a good CI.

Fig. 4 is a diagram explaining the principle of the crystal resonator according to the present invention, and shows the cross section of a rod-shaped blank plate and the strain distribution in a certain half period when it is vibrated with bending vibration on the x, z' coordinates. It is something.

In this vibration, the strain is almost uniform in the Z' force direction, changes almost linearly in the X direction as shown in the figure, becomes zero at the center, and reverses its sign.

In order to excite strongly, the lines of electric force must pass through this area of large strain as much as possible.

FIG. 5 is a perspective view showing one embodiment of the present invention, and FIG.
The figure is a cross-sectional view taken along the line ■-■ in FIG.

In the figure, 1 is a rod-shaped crystal piece, and 10a is an electrode formed on the side surface of the rod-shaped crystal piece 1.

In the present invention, the width of the electrode 11a formed on the main surface of the vibrator is set to 55 to 80% of the width of the main surface so that the electric field as described above is formed.

That is, if the width of the electrode 11a formed on the main surface is gradually narrowed from a value equal to the width of the main surface, it becomes possible to excite the electrode 11a with increasing force as described above.

However, if it is made too narrow, the distortion near the center is originally small as shown in FIG. 4, so passing electric lines of force will not lead to improvement in excitation.

According to experiments, the optimal width of the electrode 11a located on the main surface is about 70% of the width of the main surface, and a practically good CI value was obtained in the range of 55 to 80%.

The graph shown in Figure 7 has a resonance frequency of 32.768KHz.
Width W of the main surface and width E of the electrode of the rod-shaped bending vibration type crystal resonator
It shows the crystal impedance CI and the capacitance ratio Co/CI versus the ratio of Co/CI.

This vibrator has a thickness of 0.1 mm and a width of 0.7 mm1.
Electrodes are formed on a crystal resonator piece having a length of 6.6 mm and having a cross-sectional shape as shown in FIG.

As is clear from this graph, when the width E of the electrode provided on the main surface is in the range of 55 to 80% of the width W of the main surface, CI is lowest and good characteristics can be obtained.

FIG. 8 shows another embodiment of the present invention, and FIG. 9 is a diagram showing the electrode arrangement and electric field in a cross section taken along the line 111-1 in FIG. 8.

In this example, for convenience of mask configuration during vapor deposition and convenience of electrode connection, as shown in FIG.
A part of it protrudes from the main surface of the crystal piece.

If the width of this protrusion becomes too large, it will inhibit the excitation as is clear from the strain distribution already mentioned, so it is preferable to keep it to 8% or less of the width of the main surface of the crystal piece.

The graph shown in FIG. 10 shows the change in crystal impedance CI with respect to the ratio of the width W of the main surface to the width by which the side electrode protrudes into the main surface.

The vibrator used here has the same shape as the vibrator shown in the graph of FIG. 7, and the ratio of the electrode width W to the width W of the main surface is 3.
Measurements were made for two types: 5% and 44%.

As is clear from this graph, good characteristics can be obtained when the protruding width of the main surface is 8% or less of the width W of the main surface.

As described in detail above, the present invention can be applied to thin rod-shaped bending vibration type crystal resonators that can be processed by photoetching.
It is possible to provide a small crystal oscillator that has an electrode shape and arrangement that enables strong excitation, has a low impedance level, and is suitable for mass production.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an example of a conventional rod-shaped crystal resonator, FIG. 2 is a cross-sectional view taken along line 1-I in FIG. 4 is a diagram explaining the present invention in detail, FIG. 5 is a perspective view showing a crystal resonator according to an embodiment of the present invention, FIG. 6 is a sectional view taken along the line ■-■ in FIG. 5, and FIG. A graph showing the relationship between the electrode width, crystal impedance, and capacitance ratio of the above embodiment, FIG. 8 is a perspective view showing another embodiment of the present invention, FIG. 9 is a cross-sectional view taken along the line 10
The figure is a graph showing the relationship between the protruding width of the electrode and the crystal impedance. 1... Crystal piece, 10a, 11a...
electrode.

Claims (1)

[Claims] 1. In a bending vibration type rod-shaped crystal oscillator formed from a thin quartz crystal plate whose thickness is sufficiently small relative to its width, one electrode is placed on the side of the oscillator, and the other electrode is placed on the center of the main surface of the oscillator. The width of the electrode formed on the flat surface is set to 55% to 80% of the width of the main surface of the vibrator, and the width of the side electrode protruding into the main surface is suppressed to 8% or less of the width of the main surface. A crystal oscillator featuring