JPS5843926B2 - Crystal oscillator - Google Patents

Description

[Detailed description of the invention] The present invention relates to a crystal resonator that performs bending vibration.

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.

For example, a tuning fork-shaped crystal resonator that performs bending vibration is small and has excellent vibration and shock resistance properties, so it is widely used as a reference resonator for electronic wristwatches.

Traditionally, such transducers have been processed using mechanical methods such as diamond wheel cutters or ultrasonic processing, but recently, in order to improve productivity and downsize the transducers, chemical processing using photoetching has been used to reduce the thickness of the transducers. The use of standard methods is being practiced.

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 tuning fork-shaped crystal resonator processed by a conventional mechanical method, and FIG. 2 is a cross-sectional view taken along the line n--■ in FIG.

In the figure, XtY and Z are the crystal axes of the crystal, and 1 in the figure indicates the Y and Z axes centered on the X axis of the crystal, α, that is, O
Rotate ~ +8 degrees to make the X-axis, Y'-axis, and Z' orthogonal to each other.
This is a tuning fork-shaped crystal piece made of a known rotating X-plate cut out along the axis.

How to take these coordinate axes and angles is explained in "Unification of representation and symbology regarding crystal piezoelectricity" by Issaku Shimuga, 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.

Note that a known NT plate or the like may be used as the crystal piece 1.

And 2a is an electrode formed on the side of one leg 2, 3a
is an electrode formed on the main surface of the other leg 3, and this electrode 2a
.

3a is electrically connected.

Further, 2b is an electrode formed on the main surface of one leg 2, 3b is an electrode formed on the side surface of the other leg 3, and this electrode 2b
, 3b are electrically connected.

and the electrode 2a. Piezoelectric vibration is excited by applying a high frequency voltage between 3a, 2b, and 3b.

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

As is clear from the polarity, the strain in the Y-axis direction is as shown in the figure, with the center line of each leg of the tuning fork as the boundary, and if the outer side is ■, the inner side is in the opposite phase to e, and the desired bending vibration is achieved. is excited.

The resonance frequency of such a tuning fork vibrator is determined mainly by the length in the Y-axis direction and the width of the joint and the leg in the X-axis direction, and has little to do with the thickness in the Z-axis direction.

Therefore, this thickness can be made extremely thin, and with such a thin thickness, it is possible to cut out a large number of identically shaped tuning fork-shaped blanks at once from a large blank by photo-etching. It has become.

Further, the electrodes 2a and 3b to be formed on the side surfaces can be easily formed by cutting out a tuning fork-shaped blank plate and then depositing the electrodes on the blank plate individually or by stacking several electrodes.

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

The reason for this is that, as shown in FIG. 3, the electric field is concentrated at the four corners, and the lines of electric force hardly pass through areas where the strain is sufficiently large, as will be described later, so that effective piezoelectric excitation cannot be performed.

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 easy to excite.

FIG. 4 is a diagram illustrating the principle of the crystal resonator according to the present invention, and shows the cross section of one leg of a tuning fork-shaped blank plate and the strain distribution in a certain half cycle when exciting bending vibration, x,
It is shown on the z' coordinate.

Further, FIG. 5 is a perspective view showing an embodiment of the present invention,
FIG. 6 is a cross-sectional view taken along the line Vl--Vl in FIG. 5.

In the figure, 1 is a tuning fork-shaped crystal piece, 11a is an electrode formed on the side surface of one leg 11, 12a is an electrode formed on the main surface of the other leg 12, and these electrodes 11a and 12a are the base 1 of the tuning fork.
They are electrically connected via the No. 3 connection electrodes 13a.

Further, 11b is an electrode formed on the main surface of one leg 11;
Reference numeral 2b denotes an electrode formed on the side surface of the other leg 12, and these electrodes 11b and 12b are electrically connected via a connecting electrode 13b on the base 13 of the tuning fork.

In such vibration of a tuning fork, the strain is almost uniform in the Z 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.

Therefore (in the present invention, the electrode 1 formed on the main surface of the vibrator
The width w1 of 1b and 12a was set to 30 to 50 times the width w2 of the main surface so that the electric field as described above was formed.

In other words, if the width of the electrodes 11b and 12a formed on the main surface is gradually narrowed from a value equal to the width of the main surface of the leg, it becomes possible to excite the electrodes gradually in a stronger manner 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 various analyzes and experiments, the optimal width of the electrodes 11b+12a located on the main surface of the leg is about 40% of the width of the main surface of the leg, and a range of 30 to 50 is practically good. vibration characteristics were obtained.

The above is a case where the device is used as two terminals, but when used in a filter or the like, three terminals can be used by separating the electrodes 11a and 12a or 11b and 12b.

In addition, for convenience of mask configuration during vapor deposition and convenience of electrode connection, as shown in FIG.
When a part of 2b protrudes from the main surface of the tuning fork-shaped crystal piece 1, if the width W3 of this protruding portion 14 becomes too wide,
As is clear from the strain distribution already mentioned, the width must be 20% or less of the width of the main surface of the leg because it inhibits excitation.

In this way, the fact that a part of the side electrode 11at12b exists on the main surface as a protruding portion 14 of 20% or less of its width is particularly important for a thin vibrator when the side electrode 11a,
If a sufficient area cannot be obtained for 12b, the area is substantially increased, which is preferable in terms of excitation characteristics.

In this case, the width of the protruding portion 14 is 20% of the width of the main surface.
The excitation characteristics will not be particularly impaired as long as it is less than or equal to 1.

Furthermore, the existence of this protruding portion 14 is extremely convenient for ensuring electrical connection between each electrode.

That is, in order to electrically connect the side electrode of one leg and the electrode on the main surface of the other leg, the electrical connection must be made at the ridge where the side surface and the main surface intersect.

However, at such edges, the electrical connection state is more likely to become unstable due to unevenness in the thickness of the deposited film, defects in the deposited film due to mechanical stress, etc., compared to flat parts.

However, by making the side electrodes protrude from the main surface, it is possible to widen the circuit width extending beyond the ridge to the main surface, thereby making it possible to obtain a reliable electrical connection.

In this way, high-quality vibrators can be obtained in large quantities and at low cost by photoetching, vapor deposition, etc.

In particular, high productivity can be obtained by rationally connecting the main surface and inner/outer surface electrodes of the crystal piece 1 via its base.

Further, although the above description has been made regarding a tuning fork type that performs bending vibration, it goes without saying that the present invention can also be applied to a bending vibrator with free ends.

As described in detail above, the present invention provides an electrode shape arrangement that enables strong excitation even in a thin bending vibration crystal resonator that can be processed by photoetching.
It is possible to provide a small crystal resonator with a low impedance level and suitable for mass production.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a conventional tuning fork-shaped crystal resonator;
FIG. 2 is a cross-sectional view taken along the line ■-■ in FIG. 1. FIG. 3 is a diagram showing the vibration state of the vibrator in FIG. 1. FIG. FIG. 6 is a perspective view of a crystal resonator according to an embodiment of the present invention, and is a sectional view taken along the line Vl-VI in FIG. 1... Crystal piece, 11a, 11b, 12a
, 12b... Electrode.

Claims (1)

[Claims] 1. In a tuning fork-type crystal resonator that performs bending vibration, electrodes are formed on both main surfaces and both inner and outer surfaces of each leg of the tuning fork so as to be mutually insulated, and the width of the electrode formed on the main surface is determined by the width of the resonator. The electrodes formed on the side surfaces should extend from 30% to 50% of the width of the main surface of each leg by 20% or less of the width of the main surface, and the electrodes on the main surface of one leg should protrude from the base of the tuning fork and above. connect the electrode on the main surface of the other leg to the electrode on the side of one leg through the base of the tuning fork and the protruding part above, and A crystal resonator characterized in that electrodes formed on the inner surface are connected via the main surfaces of the leg tips.