JP2003115741A - Piezoelectric vibrator and overtone frequency adjustment method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] The present invention does not affect the fundamental wave resonance frequency.
An object of the present invention is to provide a piezoelectric vibrator capable of adjusting only a resonance frequency related to a third overtone. A piezoelectric vibrator in which a partial electrode and a lead electrode having predetermined dimensions are formed on two main surfaces of a piezoelectric substrate, respectively, wherein at least one of the lengths in the x direction or the z direction is the length of the portion. By laminating a vapor deposition film of a predetermined shape having a dimension shorter than the electrode at a substantially central position on the partial electrode, only the resonance frequency related to the third overtone can be adjusted without affecting the fundamental wave resonance frequency. A piezoelectric vibrator characterized by the following.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode structure of a piezoelectric vibrator, and more particularly to a means and method for adjusting only the third overtone resonance frequency without affecting the fundamental wave resonance frequency.

[0002]

2. Description of the Related Art In recent years, piezoelectric vibrators, such as AT-cut quartz crystal vibrators, have been widely used in mobile phone terminals, personal computers, etc. due to their small size and the ability to easily obtain highly accurate and stable frequencies. Has been done.

FIGS. 8A and 8B are views showing the structure of a conventional surface mount type crystal unit. FIG. 8A is a plan view and FIG. 8B is a sectional view taken along QQ. Partial electrodes 82a and 82b are attached to opposing positions on both main surfaces of the AT-cut quartz crystal substrate 81 cut out in a strip shape, and lead electrodes 83a and 83b are extended toward the ends of the quartz crystal substrate 81, respectively. To form the crystal unit X. Further, the crystal unit X is housed in a ceramic package (not shown), its lead electrodes 83a and 83b are conductively fixed to the package terminal electrodes using a conductive adhesive, and the metal lid is hermetically sealed by resistance welding or the like. It is common to stop and configure a crystal oscillator.

FIG. 9 is a diagram showing the resonance characteristics of the crystal unit X. Based on the width (w) and the thickness (t) of the quartz substrate 81, the resonance frequency f1 in the fundamental wave mode is given by the following equation f1 = K / t (1) where K is a constant of the material. Further, as is well known, in addition to this f1, a third overtone resonance frequency 3f1 occurs at a frequency three times f1.

Given the frequency to be used, the above (1)
The thickness t of the quartz substrate 81 is uniquely determined by the equation,
Since the t changes equivalently and the resonance frequency fluctuates due to the attachment of the partial electrodes 82a and 82b described above, it is necessary to finely adjust the resonance frequency.

FIG. 10 is a cross-sectional view of essential parts for explaining the conventional fine adjustment of the resonance frequency in the crystal unit. The figure (a) shows the structure which adds a vapor deposition film, and the figure (b) shows the structure which performs fine adjustment by electrode removal, respectively. First, in FIG. 6A, one of the partial electrodes 82a and 82b formed on both main surfaces of the crystal substrate 81 is further provided with a vapor deposition film.
By adding 101 to the entire surface of the partial electrode, the equivalent thickness t of the crystal substrate 81 is increased, and the fine adjustment is performed to lower the resonance frequency. Further, FIG. 2B shows that the electrode film is thinned by performing ion etching on almost the entire surface of the partial electrode, and the equivalent thickness t of the quartz substrate is thinned to make a fine adjustment to increase the resonance frequency. It's something that you do. By using such means, the resonance frequency can be adjusted to a desired value.

[0007]

However, the above-described crystal unit has the following problems. In other words, the resonance frequency of the third-order overtone, which is a harmonic component, is in the vicinity of the value obtained by multiplying the fundamental wave frequency by three, so the crystal oscillator is configured using the fundamental wave frequency of the crystal oscillator, and its output frequency is When multiplying by 3 in the multiplier circuit, the output from this multiplier circuit interferes with the output of the third overtone frequency from the crystal oscillator, and the desired frequency cannot be obtained, or the frequency is adjusted. The problem occurs that it becomes difficult. Therefore, in such applications, there has been an increasing demand for the third overtone resonance frequency to be kept as far as possible from the value obtained by multiplying the fundamental frequency of the crystal unit by three. By the way, the third-order overtone resonance frequency depends on the area of the partial electrode. Therefore, when only the third-order overtone resonance frequency needs to be adjusted, the area of the partial electrode is increased. A method of reducing the partial electrode area may be considered, but this is not usually used because the equivalent capacitance of the vibrator becomes small and the frequency adjustment range becomes narrow. However, in recent years, it has become difficult to increase the area of the partial electrodes due to the increasing demand for miniaturization from users. In this case, if the fine frequency adjustment as shown in FIG. 10 is performed to shift the third-order overtone resonance frequency by a predetermined amount, the fundamental wave resonance frequency is also shifted from the predetermined value at the same time. The present invention has been made to solve the above-mentioned problems relating to the electrode structure of the piezoelectric vibrator related to the fine frequency adjustment of the related art, and only the resonance frequency related to the third overtone is adjusted without affecting the fundamental wave resonance frequency. It is an object of the present invention to provide a possible piezoelectric vibrator.

[0008]

In order to achieve the above-mentioned object, the invention according to claim 1 of the piezoelectric vibrator according to the present invention is such that partial electrodes are provided on two main surfaces of a piezoelectric substrate and the partial electrodes extend from the partial electrodes. A piezoelectric vibrator having a thickness-shear mode as a main vibration, each of which has a lead electrode, and a strip-shaped convex portion having a width narrower than that of the partial electrode is formed substantially at the center of the upper surface of the partial electrode. The invention according to claim 2 of the piezoelectric vibrator according to the present invention is a piezoelectric vibration whose main vibration is a thickness-sliding mode in which two main surfaces of a piezoelectric substrate each have a partial electrode and a lead electrode extending from the partial electrode. As a child, a band-shaped concave portion having a width narrower than that of the partial electrode is formed substantially at the center of the partial electrode. The invention according to claim 3 of the third-order overtone frequency adjusting method for a piezoelectric vibrator according to the present invention is characterized in that a thickness slide provided with partial electrodes and lead electrodes extending from the partial electrodes on two main surfaces of a piezoelectric substrate, respectively. A method of adjusting the third-order overtone frequency of a piezoelectric vibrator having a mode as a main vibration, which is measured in the frequency measurement step of measuring the third-order overtone frequency of the piezoelectric vibrator and in the frequency measurement step. A vapor deposition step of vapor-depositing a strip-shaped metal film having a width narrower than that of the partial electrode when the tertiary overtone frequency is higher than the desired value, at a substantially center of the upper surface of the partial electrode. The above steps were repeated until. The invention according to claim 4 of the third-order overtone frequency adjusting method for a piezoelectric vibrator according to the present invention is characterized in that a thickness slide having two partial electrodes and lead electrodes extending from the two partial electrodes on the two main surfaces of the piezoelectric substrate. A method of adjusting the third-order overtone frequency of a piezoelectric vibrator having a mode as a main vibration, which is measured in the frequency measurement step of measuring the third-order overtone frequency of the piezoelectric vibrator and in the frequency measurement step. An etching step of forming a band-shaped recess narrower than the partial electrode by etching at a substantially central portion of the partial electrode when the third overtone frequency is lower than the desired value. The above steps were repeated until.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below based on the illustrated embodiments. FIG. 1 is a perspective view showing an embodiment of an electrode structure of a piezoelectric vibrator according to the present invention and a cross-sectional view of a main part as seen from the width direction. The electrode structure of the piezoelectric vibrator shown in this example has partial electrodes 12a and 12b and lead electrodes 13a and 13b (1
3b is not shown), and the partial electrode 12a is formed in the x direction.
A rectangular vapor deposition film 14 having the same length as that in the z direction and having a dimension (w2) shorter than the width (w1) of the partial electrode 12a is laminated at a substantially central position of the partial electrode 12a.

A feature of the present invention is that the vapor deposition film 14 is formed on the partial electrode 12a.
The reason is that the layers are not laminated on the entire surface, but are laminated on a part of the partial electrode surface and at a substantially central position for the reason described later. FIG. 2 is a diagram showing an amplitude distribution related to vibration in the width direction (z direction) of the piezoelectric vibrator. This figure is obtained as a result of a simulation using the finite element method by the inventor of the present application. The horizontal axis represents the position of the partial electrode in the width direction as a ratio of the total width, 0% and 10
0% represents both ends of the electrode, 50% represents the center position of the electrode, and the vertical axis represents the amplitude distribution of vibration normalized by the maximum value in the fundamental resonance mode.

As shown in FIG. 2, at the central position of the electrode, the amplitude value of the third overtone resonance mode is about 1.4 times larger than that of the fundamental wave resonance mode, and ± 20% from the center.
The third-order overtone resonance mode is larger than the fundamental resonance mode at the electrode position. Therefore, the band-shaped electrode film 14 for frequency fine adjustment with a width of 40% or less is formed in the center of the electrode.
It is considered that the ratio that influences the third-order overtone resonance frequency is increased by adding.

FIG. 3 is a diagram showing an example of deviation of the fundamental wave resonance frequency and the third-order overtone resonance frequency with respect to the vapor deposition film width (w2) of the piezoelectric vibrator according to the present invention. w1 / w2 = 1 indicates the case where the vapor deposition film is laminated on the entire surface of the partial electrode, and the fundamental wave resonance frequency and the third overtone resonance frequency are adjusted to predetermined values. From this state, if the vapor deposition film width (w2) is gradually shortened and the film thickness is increased accordingly, the deviation of the third overtone resonance frequency should be increased without affecting the fundamental resonance frequency. You can

As described above, when the electrode structure of the piezoelectric vibrator according to the present invention is used, even if the third overtone resonance frequency is deviated from the predetermined value, the fundamental wave resonance frequency is not affected.

In the embodiments described above, the structure of frequency fine adjustment in which a vapor deposition film is added has been described, but a recess may be formed in the partial electrode instead of the vapor deposition film. FIG. 4 is a cross-sectional view of an essential part of the electrode structure of a piezoelectric vibrator as a second embodiment according to the present invention as viewed in the width direction. The electrode structure of the piezoelectric vibrator shown in this example is
Instead of stacking vapor deposited films in the structure shown in FIG. 1,
A recess 41 having the same area as the vapor deposition film was formed on one of the partial electrodes 12a.

With such a configuration, only the third overtone resonance frequency can be finely adjusted for the same reason as the structure shown in FIG. 1 in which the vapor deposition film is added, but in the second embodiment, it is equivalent. Since the thickness of the piezoelectric substrate is reduced, the frequency to be adjusted is lowered below the reference value.

FIG. 5 is a perspective view showing a third embodiment of the electrode structure of the piezoelectric vibrator according to the present invention.
The electrode structure of the piezoelectric vibrator shown in this example has a vapor deposition film 51 shorter than the partial electrode 12a in the x direction by l2 and the same as the partial electrode 12a in the z direction as compared with the embodiment example shown in FIG. It is made to have a length and is laminated at a substantially central position of the partial electrode 12a.

FIG. 6 is a diagram showing an amplitude distribution relating to vibration in the length direction (x direction) of the piezoelectric vibrator. This figure is obtained as a result of a simulation using the finite element method by the inventor of the present application similarly to FIG. The horizontal axis represents the position of the partial electrode in the x direction as a ratio of the total length (l1), and is shown for one half from the center of the partial electrode. 0% represents the center position of the electrode, 100% represents one end, and the vertical axis represents the amplitude distribution of vibration normalized by the maximum value in the fundamental resonance mode. Note that the maximum value of the third-order overtone resonance mode does not match the corresponding value shown in FIG. 2, but this is the effect of independently calculating each simulation in the z direction and the x direction.

At the electrode center position, the amplitude of the third-order overtone resonance mode becomes larger than that of the fundamental wave resonance mode, which is similar to the result in the z direction shown in FIG.

FIG. 7 is a diagram showing an example of deviation of the fundamental wave resonance frequency and the third-order overtone resonance frequency with respect to the third embodiment of the present invention. Similar to the first embodiment shown in FIG. 3, the length (l2) of the vapor deposition film 51 is sequentially shortened and the film thickness is increased accordingly, so that only the third-order overtone resonance frequency is greatly shifted. Can be made.

It should be noted that it is not necessary to particularly explain that instead of the vapor-deposited film 51, a recess may be formed in the partial electrode as in the second embodiment.

In the above embodiments, the case where the vapor deposition film dimension (recess dimension) is made shorter in the z direction or in the x direction than the partial electrode has been described, but of course, the dimensions in both directions can be shortened at the same time. The effects of the present invention are the same, and the shape thereof is not limited to a rectangle, and may be an ellipse or an arbitrary polygon. In short, according to the present invention, a vapor deposition film (recess) having a shape shorter than the partial electrode is formed at a substantially central position of the partial electrode where the vibration amplitude distribution of the third overtone resonance mode is larger than that of the fundamental resonance mode. It should be set to.

[0022]

As described above, according to the present invention, a vapor deposition film having a dimension shorter than that of the partial electrode is laminated at a substantially central position of the partial electrode, or a recess having the same dimension as the vapor deposition film is formed in the partial electrode. Since this is done, it is extremely effective in realizing a piezoelectric vibrator that can finely adjust only the third-order overtone resonance frequency without affecting the fundamental wave resonance frequency.

[Brief description of drawings]

FIG. 1 is a perspective view showing an electrode structure of a piezoelectric vibrator according to the present invention and a cross-sectional view of a main part as seen from a width direction.

FIG. 2 is a diagram showing an amplitude distribution of vibration in a width direction (z direction) of a piezoelectric vibrator.

FIG. 3 is a diagram showing an example of deviation of a resonance frequency of a fundamental mode and a third-order overtone with respect to a vapor deposition film width of a piezoelectric vibrator according to the present invention.

FIG. 4 is a cross-sectional view of an essential part of the second embodiment of the electrode structure of the piezoelectric vibrator according to the present invention, as viewed from the width direction.

FIG. 5 is a perspective view showing a third embodiment of the electrode structure of the piezoelectric vibrator according to the invention.

FIG. 6 is a diagram showing the amplitude distribution of vibration in the length direction (x direction) of the piezoelectric vibrator.

FIG. 7 is a diagram showing an example of deviation of the resonance frequency of the fundamental mode and the third overtone with respect to the vapor deposition film length of the piezoelectric vibrator according to the present invention.

FIG. 8 is a plan view showing a structure of a conventional surface mount crystal unit and a cross-sectional view at QQ.

[Figure 9] Diagram showing the resonance characteristics of a crystal unit

FIG. 10 is a sectional view of an essential part for explaining the conventional fine adjustment of the resonance frequency in the crystal unit.

[Explanation of symbols]

..Piezoelectric substrate 12a ... Partial electrodes 13a ... Lead electrodes 14 ... Evaporated film

Claims (4)

[Claims] 1. A piezoelectric vibrator having a thickness-shear mode as a main vibration, comprising a partial electrode and lead electrodes extending from the partial electrode on two main surfaces of a piezoelectric substrate, wherein the upper surface of the partial electrode is substantially the same. A piezoelectric vibrator, wherein a strip-shaped convex portion having a width narrower than that of the partial electrode is formed in the center. 2. A piezoelectric vibrator having a thickness-shear mode as a main vibration, comprising a partial electrode and lead electrodes extending from the partial electrode on two main surfaces of a piezoelectric substrate, wherein the piezoelectric vibrator is substantially at the center of the partial electrode. A piezoelectric vibrator, wherein a band-shaped recess narrower than the partial electrode is formed in the. 3. A method of adjusting a third overtone frequency of a piezoelectric vibrator having a thickness-shear mode as a main vibration, which has partial electrodes and lead electrodes extending from the partial electrodes on two main surfaces of a piezoelectric substrate, respectively. And a frequency measuring step of measuring a third overtone frequency of the piezoelectric vibrator, and substantially the center of the upper surface of the partial electrode when the third overtone frequency measured in the frequency measuring step is higher than a desired value. And a vapor deposition step of vapor-depositing a strip-shaped metal film narrower than the partial electrode, and repeating the above steps until the third overtone frequency reaches a desired value. Adjustment method. 4. A method of adjusting a third overtone frequency of a piezoelectric vibrator having a thickness-shear mode as a main vibration, which includes a partial electrode and lead electrodes extending from the partial electrode on two main surfaces of a piezoelectric substrate, respectively. And a frequency measuring step of measuring a third overtone frequency of the piezoelectric vibrator, and when the third overtone frequency measured in the frequency measuring step is lower than a desired value, the partial electrode is substantially centered. A third overtone frequency of a piezoelectric vibrator, comprising: an etching step of forming a band-shaped recess narrower than the partial electrode by etching, and repeating the above steps until the third overtone frequency reaches a desired value. Adjustment method.