JPS5829648B2 - How to adjust the natural frequency of a tuning fork crystal resonator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for adjusting the natural frequency of a tuning fork type piezoelectric vibrator.

An object of the present invention is to simplify the method for adjusting the natural frequency of a tuning fork type piezoelectric vibrator.

Another object of the present invention is to expand the maximum adjustment range of the natural frequency of a tuning fork type piezoelectric vibrator.

Recently, corrosion removal processing has been put into practical use as a manufacturing method for ultra-small piezoelectric vibrators, and several to several dozen piezoelectric vibrators can be manufactured simultaneously from a single thin piezoelectric material wafer using photoetching technology. Processed.

However, the natural frequency of the piezoelectric vibrator within the same web is 0.
There is a variation of about 1% to 1%, and if the variation due to different wafers is included, the natural frequency of the piezoelectric vibrator after corrosion removal processing has an error of about 1% to several% with respect to a predetermined frequency.

Furthermore, tuning fork type piezoelectric vibrators manufactured by conventional machining have similar errors.

However, when a piezoelectric vibrator is used as a circuit element, especially as a time standard for an electronic clock, the accuracy of the natural frequency of the piezoelectric vibrator must be within several tens of pp [Il] for a given frequency. Therefore, it is necessary to adjust the natural frequency of the piezoelectric vibrator.

Conventional methods for adjusting the natural frequency of a tuning fork type piezoelectric vibrator generally include a method using mechanical cutting using a diamond wheel or the like, which will be described below, and a method using laser light irradiation.

FIG. 1 shows a schematic diagram of a conventional method for adjusting the natural frequency using a diamond wheel.

In FIG. 1, 1 is a machined tuning fork type piezoelectric vibrator, and 2 is a diamond wheel.

This method mainly involves cutting the tip of the tuning fork arm with a diamond wheel to change the mass, thereby adjusting the natural frequency to be higher.

However, this method can be made thinner by corrosion removal processing,
When applied to miniaturized piezoelectric vibrators, problems such as cracks and chips occur, and it becomes extremely difficult to adjust the natural frequency of the piezoelectric vibrators.

Furthermore, the natural wave number shift after natural frequency adjustment due to the occurrence of mechanical strain becomes large.

Therefore, a natural frequency adjustment method using laser light irradiation has been developed for the purpose of compensating for these drawbacks for thin and small piezoelectric vibrators.

FIG. 2 shows a specific example of a method for adjusting the natural frequency by laser beam irradiation.

In FIG. 2, numeral 3 is a small tuning fork type piezoelectric vibrator which has been subjected to corrosion removal processing, numeral 4 is a metal film for adjusting the natural frequency provided on the tuning fork arm of the piezoelectric vibrator, and numeral 5 is a laser beam.

This method continuously measures the natural frequency of a piezoelectric vibrator, irradiates it with laser light, removes a certain amount of the metal film, and changes the mass to adjust the natural frequency to a higher value. It is.

However, in this method, the adjustment width of the natural frequency depends on the mass of the metal film, and when a large amount of laser light is irradiated, the natural frequency shifts due to thermal distortion, so the accurate natural frequency can be adjusted. Frequency adjustment becomes difficult.

Therefore, in general, the maximum adjustment range of the natural frequency by laser beam irradiation is approximately 1% of the natural frequency of the piezoelectric vibrator.

Furthermore, although this method can adjust piezoelectric vibrators having a natural frequency lower than a predetermined frequency as described above,
This method has the disadvantage that piezoelectric vibrators with high natural frequencies cannot be adjusted.

Therefore, when adjusting the natural frequency by laser light irradiation, it is necessary to process the piezoelectric vibrator so that its natural frequency is lower than a predetermined frequency, and to make the error between the two smaller than the maximum adjustment width by laser light irradiation. be.

For this reason, when the conventional frequency adjustment force method is used, a piezoelectric vibrator with high dimension precision is required, and if the required precision is not satisfied, the yield cannot be reduced.

Furthermore, the smaller the piezoelectric vibrator is, the greater the dimensional accuracy becomes relative to the natural frequency, so a piezoelectric vibrator with even higher dimensional accuracy is required.

In other words, one of the major problems that hinders the production of ultra-small piezoelectric vibrators is that the maximum adjustment range of the natural frequency is small.

The present invention solves these drawbacks, and after forming the electrodes of the piezoelectric vibrator, the metal film serving as the electrode of the piezoelectric vibrator is coated with corrosion-resistant material in order to change the cross-sectional shape of the tuning fork arm of the piezoelectric vibrator. Corrosion processing is applied to the entire piezoelectric vibrator as a membrane,
This adjusts the natural frequency of the piezoelectric vibrator.

FIG. 3 shows an embodiment of the present invention.

FIG. 3A is a plan view after forming electrodes of a piezoelectric vibrator by corrosion removal processing, FIG. 3B is an enlarged cross-sectional view of one arm of the tuning fork arm, and FIG. 3B is XX' FIG. 3C shows the state before the natural frequency adjustment in the cross section, and FIG. 3C shows the state after the natural frequency adjustment in the xx' cross section.

In FIG. 3, according to the present invention, a piezoelectric vibrator 3 is provided with electrodes 6 and 7 made of metal films, and the electrodes 6 and 7 are provided with electrodes 6 and 7 made of metal films. The entire piezoelectric vibrator 3 is immersed in a corrosive liquid using γ as a corrosion-resistant film, and a recess 10 is formed on the plate surface of the piezoelectric vibrator 3 other than the electrode portion where the electrodes 6 and 7 are not provided, This method of adjusting the frequency of a piezoelectric vibrator is characterized in that the natural frequency is adjusted to be lower by the amount of change in the recess 10 (the amount of change in the depth t of the recess 10).

Next, the metal film serving as the electrode of the piezoelectric vibrator is treated as a corrosion-resistant film, and the cross-sectional shape of the tuning fork arm is changed, and the natural frequency of the piezoelectric vibrator can be adjusted in the direction of lowering. This will be explained using a formula for the natural frequency of a general tuning fork type piezoelectric vibrator with one end fixed.

When the natural frequency to be found is f, f is found by the following equation.

In equation (1), f is the natural frequency, l is the tuning fork arm length,
m is 1.875 (fundamental vibration), A is the cross-sectional area of the tuning fork arm, ■
are the moments of inertia with respect to the O-axis and P-axis in FIG. 3 R and C, E is Young's modulus, and ρ is density.

By changing the cross-sectional shape from a rectangular shape to a shape having a recess 10 as shown in FIG.
It can be understood that this decreases, and therefore the natural frequency of the piezoelectric vibrator can be adjusted to lower.

Next, FIG. 4 shows an example of application of the present invention.

Figure 4A is a sketch of the machined tuning fork type piezoelectric vibrator shown in Figure 1, B and C are enlarged cross-sectional views of one arm of the tuning fork arm, and B is the natural frequency adjustment in the Y-Y' cross section. The previous state and C show the state after natural frequency adjustment in the Y-Y' cross section.

In FIG. 4, 1 is a tuning fork type piezoelectric vibrator, and 8 and 9 are two electrodes made of a metal film provided on the piezoelectric vibrator.

By performing corrosion processing on the piezoelectric vibrator using the electrode as a corrosion-resistant film, the cross-sectional shape changes to a shape having a recess 11 as shown in FIG.
A becomes smaller, and the natural frequency can be lowered.

In this way, in any electrode structure, the natural frequency can be lowered by changing the cross-sectional shape of the tuning fork arm.

Here, the amount of change in the natural frequency is the recess 11 due to corrosion processing.
The depth t is proportional to the depth t, and the depth t can be made as deep as it does not affect the strength of the tuning fork arm.

Therefore, in the present invention, the adjustment range of the natural frequency can be up to several percent of the natural frequency of the piezoelectric vibrator.

Furthermore, in the present invention, the corrosion rate can be arbitrarily selected by appropriately selecting the composition, temperature, etc. of the corrosive solution, so the adjustment speed of the natural frequency can be adjusted from 1% per minute to 100pp per minute.
It can be varied up to about Il.

Further, if the corrosive liquid is constant, the corrosion rate is also constant, so the amount of adjustment of the natural frequency can be determined simply by managing the time of immersion in the corrosive liquid.

Further, according to the present invention, since no mechanical strain or thermal strain is generated, an adverse effect on the performance of the piezoelectric vibrator can be eliminated.

Furthermore, the present invention allows a combination in which a piezoelectric vibrator whose natural frequency is higher than a predetermined frequency is coarsely adjusted to a position slightly lower than the predetermined frequency, and then finely adjusted by laser beam irradiation.

In that case: 1. Piezoelectric vibrators whose natural frequencies are both higher and lower than a predetermined frequency can be used.

2. The amount of laser light irradiation can be reduced compared to performing rough adjustment to fine adjustment only by laser light irradiation.

There are advantages such as

As described above, according to the present invention, the natural frequency adjustment of a small piezoelectric vibrator can be easily performed, and the maximum adjustment range can also be expanded.

You can get very big effects.

[Brief explanation of the drawing]

Figure 1 shows a conventional natural frequency adjustment method using a diamond wheel. Figure 2 shows a conventional natural frequency adjustment method using laser beam irradiation. Figure 3 shows an embodiment of the present invention.
Figure 3B is a plan view of the piezoelectric vibrator after the electrodes are formed by corrosion removal processing, Figure 3B is a cross-sectional view of the tuning fork arm before adjusting the natural frequency, Figure 3
Figure C is a cross-sectional view of the tuning fork arm after natural frequency adjustment, Figure 4 is an application example of the present invention, Figure 4A is a sketch of a piezoelectric vibrator by machining, and Figure 4B is a cross-sectional view of the tuning fork arm before natural frequency adjustment. 4C is a cross-sectional view of the tuning fork arm after natural frequency adjustment; 1 is a tuning fork type piezoelectric vibrator by machining; 2 is a diamond wheel; 3 is a tuning fork type piezoelectric vibrator by corrosion removal process; 4 is a metal film for adjusting natural frequency, 5 is a laser beam, 6
, 7 is an electrode provided on a tuning fork type piezoelectric vibrator processed by corrosion removal processing, 8.9 is an electrode provided on a tuning fork type piezoelectric vibrator processed by machining, and 10.11 is a recessed portion.

Claims (1)

[Claims] 1 A piezoelectric vibrator is provided with an electrode that is better than a metal film and a metal film for laser trimming to form an individual tuning fork crystal vibrator,
After measuring the natural frequency of each crystal resonator, immersing the entire crystal resonator in a corrosive liquid; forming a recess on the surface and adjusting the natural frequency of the crystal resonator to be lower than a predetermined value according to the amount of change in the recess, and then removing the laser trimming metal film with a laser to adjust the natural frequency to a predetermined value. A method for adjusting the natural frequency of a tuning fork type piezoelectric vibrator, which comprises a process of adjusting the oscillator.