JPS5850049B2 - Tuning fork type piezoelectric vibrator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to application of an electric field to a tuning fork type piezoelectric vibrator and a cutting angle of a quartz plate suitable therefor.

An object of the present invention is to put into practical use an ultra-compact, high-performance tuning fork type piezoelectric vibrator.

In recent years, there has been a remarkable movement toward electronic wristwatches, and the practical use of quartz watches in particular has progressed rapidly.

Needless to say, a quartz crystal resonator is used as the time standard for these quartz clocks, and its vibration mode is either a free-ended type or a tuning fork type.

In all of these cases, +5°
A chemical processing method has been developed in which the shape of a vibrator and its electrodes are photoetched using T-cuts.

However, the performance and dimensions of the crystal resonator due to the conventional electrode structure and cutting angle have advantages and disadvantages, and an optimal method has not been found.

Below are conventional examples of +5°X force-tuning fork type bent crystal resonators made by mechanical processing methods and NTs made by chemical processing methods.
This will be explained using a cut tuning fork type bent crystal resonator.

FIG. 1 shows an example of a +5°X-cut tuning fork crystal resonator produced by a conventional mechanical processing method, and FIG. 2 shows its electrode arrangement.

In FIGS. 1 and 2, 1 is a +5°X-cut tuning fork crystal resonator, 2 and 3 are electrodes, 2 is one electrode, and 3 is the other electrode.

The X, Y, and Z axes are the electrical, mechanical, and optical axes of the crystal, respectively.

The crystal oscillator has a Z plate with the X axis as the rotation axis and the angle α is 00 ~
10°, generally 5°.

If we apply positive and negative voltages to electrodes 2 and 3 of this vibrator, an electric field will be applied inside the crystal as shown by the curved arrow in Figure 2, and the lateral component of this electric field will be , that is, the component in the X-axis direction causes distortion.

If we consider a tuning fork with one gold side, the direction of the electric field will be opposite on the left and right halves of the center of the arm, so if one stretches, the other will contract and bend.

Although we have described one arm of the tuning fork, the same is true for the other arm.

That is, an electric field may be applied so that when one arm of the tuning fork bends inward, the other arm also bends inward.

When an alternating current voltage is applied to the electrodes, symmetrical bending vibration is excited in the crystal resonator 1.

This type of crystal oscillator has low loss resistance, so it is well coupled with the circuit, and the inflection point temperature of the temperature-frequency characteristic can be relatively easily selected at room temperature, so it is possible to improve time accuracy when used in a wristwatch. has good advantages.

However, on the other hand, as is clear from the figure, this type of vibrator requires electrodes on the side surfaces, so an electrode dividing step is required during the manufacturing process.

It also has the disadvantage that it is not possible to produce an ultra-thin crystal resonator, and because of its large thickness, it is almost impossible to obtain a tuning fork type crystal resonator by photoetching.

FIG. 3 shows an example of an NT-cut tuning fork type bent crystal resonator produced by a conventional chemical processing method, and FIG. 4 shows its electrode arrangement.

4 is a tuning fork crystal resonator, 5 is an inner electrode on the front surface and an outer electrode on the back surface, and 6 is an outer electrode on the front surface and an inner electrode on the back surface. The connection between the front electrode and the back electrode is made outside the crystal oscillator (in FIG. 3, (The back electrode is not shown).

X, Y, and Z indicate the electrical axis, mechanical axis, and optical axis of the crystal, respectively.

The oscillator in Figure 3 rotates an X plate whose tuning fork arm is parallel to the Y axis by α0 with the
It is cut out by a plate that rotates 10 times around the shaft.

Then, α is selected to be 0° to 100, and β is selected to be 60° to 75°.

Since this type of resonator has no electrodes on the side, it is possible to form a very thin resonator, so it is possible to form a tuning fork type crystal resonator by photo-etching, and it is possible to create an ultra-small and ultra-thin crystal resonator. Although it has the advantage of being easy to manufacture, it has the following drawbacks.

In Figure 4, if a positive and negative electric field is applied to the electrode 6°5, the direction of the electric field will move in the direction shown in Figure 4, but the electric field component required to actually excite the tuning fork crystal resonator Since is the X component, the larger the angle β, the smaller the X component and the less likely to cause distortion.

The X component of the electric field is given by CO8β.

In other words, the β that can be used in a watch vibrator is 60 as mentioned above.
Since the electric field component in the X direction is large at ~75[deg.], the loss resistance of the equivalent circuit of the crystal resonator is large, and it is difficult to match ICs, etc., and the current consumption is large.

As detailed above, the conventional +5° I couldn't do it.

The present invention combines the two methods and takes advantage of the advantages of both methods by adopting a new electric field application method.

FIG. 5 shows the cut angle of the piezoelectric vibrator of the present invention, and FIG. 6 shows an example of electrode arrangement of the piezoelectric vibrator of the present invention.

In FIGS. 5 and 6, 10a is a crystal resonator of the present invention.

XYZ are the electrical, mechanical and optical axes of the crystal, respectively.

The crystal oscillator is a Y plate whose tuning fork arm is parallel to the X axis.
It is cut out from a plate which is rotated by an angle α' of 00 to 90 degrees with the axis as the rotation axis, and further rotated by an angle γ of 0 to 800 degrees with the Y' axis as the rotation axis.

The selection of this cutting angle is determined by the temperature at which the inflection point of the temperature-resonant frequency characteristic is to be set.

At the same time, it is determined by the dimensions, shape, etc. of the tuning fork type crystal resonator.

11.12 is an electrode according to the invention. The front electrode and the back electrode are usually connected by the side surface (the back electrode is not shown), but they may be connected by providing a through hole or the like near the base of the tuning fork crystal resonator.

If positive and negative voltages are applied to electrodes 11 and 12, respectively, the electric field inside the crystal will be in the opposite direction on the left half and the right half of the center of the tuning fork's arm, considering one arm of the tuning fork. If one causes an elongation distortion, the other one causes a contraction distortion.

When an alternating current voltage is applied, symmetrical bending vibration is excited in the vibrator 10a.

(In Figure 6, only the electric field on the outside of the tuning fork arm is shown, and the electric field on the inside is not shown.) As shown in Figures 5 and 6, in order to excite the tuning fork type crystal resonator, the direction of the X-axis direction is In the present invention, since the electric field component is effective, the electric field direction is applied in the X-axis direction, so that the loss resistance of the crystal resonator can be reduced.

In the present invention, since excitation electrodes are not used on the side surfaces, a chemical processing method using photoetching can be used when forming the tuning fork shape and when forming the electrodes, making it possible to further downsize the vibrator.

Another advantage of the present invention is that it becomes even more effective when the frequency of the tuning fork type crystal resonator is increased.

The frequency f of the tuning fork type crystal resonator is given by fooW/L2, where W is the arm width of the tuning fork and L is the arm length of the tuning fork.

Generally, in order to increase the frequency of the oscillator, it is sufficient to reduce L, so as shown in Figures 5 and 6, the electric field density increases, the distortion becomes even larger, and the loss resistance of the equivalent circuit constant of the crystal oscillator becomes smaller. We can provide even better crystal oscillators.

In this case, the frequency that can be used is limited to 30 KHz to 800 KHz, taking into consideration the frequency stability of the tuning fork type crystal vibration.

FIG. 7 shows a specific example of another electrode arrangement of the present invention.

In FIG. 7, 13a indicates a crystal resonator, and 13.14 indicates electrodes. In FIG. 6, both sides of the tuning fork arm are driven, but in FIG. 7, one drive is performed only on one side of the tuning fork arm.

The driving and excitation principles are the same as those described in FIG.

(The back electrode is not shown in Fig. 7).Although all the explanations so far have been made using a tuning fork type crystal resonator,
It goes without saying that the present invention can be applied to both-end free type vibrators or other bending piezoelectric vibrators.

As described above, the present invention combines the advantages of both the conventional +5°X cut and the NT cut.

Furthermore, since the present invention does not require an excitation electrode on the side of the vibrator, photo-etching technology can be incorporated into the vibrator manufacturing method, making it suitable for mass production.The vibrator shape can be made smaller and thinner, making it suitable for use as a crystal vibrator for wristwatches. It is highly expected to be used.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a conventional +5°X-cut tuning fork type crystal resonator, and FIG. 2 is an electrode layout diagram of the resonator of FIG. FIG. 3 is a schematic diagram of a conventional NT-cut tuning fork type crystal resonator, and FIG. 4 is an electrode arrangement diagram of the resonator of FIG. FIG. 5 shows an example of the cut angle of the crystal resonator of the present invention. α′ and γ indicate the cutting angle of the crystal plate. FIG. 6 is a single pole arrangement diagram of the vibrator shown in FIG. FIG. 7 shows another specific example of the crystal resonator of the present invention. 13.14 in the figure shows the electrodes. 1.4.10a, 13a...Crystal resonator, 11
゜12.13.14... Electrode, α', γ...
...The cutting angle of the crystal oscillator.

Claims (1)

[Claims] 1 In a tuning fork type piezoelectric vibrator, the vibrator has a Y plate
It is cut at an angle of 00 to 900 rotations using the axis as the rotation axis, and further 00 to 800 rotations using the Y' axis as the rotation axis,
The longitudinal direction of the tuning fork arm of the vibrator is arranged parallel to the X' axis, and a pair of electrodes are provided on at least one of the inner and outer sides of the tuning fork arm of the vibrator so that an electric field is applied in the longitudinal direction of the tuning fork arm. are arranged on each of the tuning fork arms, and the two pairs of inner electrodes or the two pairs of outer electrodes apply an electric field in substantially the same direction so as to cause bending vibration in the piezoelectric vibrator. Features a tuning fork type piezoelectric vibrator.