JP2000295065A - Piezoelectric vibrator and its frequency adjusting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystal oscillator with less frequency fluctuation quantity by bonding second electrodes for frequency fine adjustment at a peripheral part except for the center parts of first electrodes provided for the centers of both faces of a piezoelectric substrate. SOLUTION: Base electrodes 2a and 2b are bonded on the centers of the surface/back of a piezoelectric substrate 1. The lead electrodes 3a and 3b of the base electrodes 2a and 2b and a holder terminal are fixed and the fine quantity of metal is vapor- deposited through an electrode for frequency adjustment 4. A frequency is adjusted to a prescribed value. The displacement distribution α of vibration after the bonding of the base electrodes 2a and 2b becomes a curve and a bottom extends from the curve by the bonding of the electrode 4 for frequency adjustment 4. The effect of energy containment becomes small. The equivalent resistance value of a crystal oscillator becomes slightly larger, namely, the Q value of main vibration becomes small and therefore series load capacity is connected to the crystal oscillator. At the time of changing capacity or when a peripheral temperature is changed, the Q value of main vibration becomes small and the fluctuation rate of equivalent resistance becomes small even if high-order outline vibration is connected to main vibration.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezoelectric vibrator,
In particular, the present invention relates to a piezoelectric vibrator in which frequency fluctuations caused by coupling of sub-vibration with main vibration are reduced.

[0002]

2. Description of the Related Art In recent years, quartz resonators, especially AT-cut quartz resonators, are small in size and can easily obtain high-precision, high-stability frequencies. Have been. Small A
Looking at the history of the development of T-cut quartz resonators (thickness shear vibrations), a great deal of effort was spent on how to avoid coupling to the main vibration due to width vibration and obtain a stable frequency over a wide range of temperatures. Have been. For example, “Study on Vibration Mode of Quartz Crystal Resonator Based on Probe Method” (Fukuyo, Tokyo Institute of Technology, 195
5) In the case where the thickness of the AT-cut quartz substrate and the length in the Z'-axis direction are constant and only the length in the X-axis direction is slightly reduced, or the thickness and the length in the X-axis direction are constant, 'When only the length in the axial direction is ground little by little, the frequency of the various vibrations excited, including the frequency of the main vibration, is precisely measured, and the vertical axis is the resonance frequency, and the horizontal axis is the length in the X-axis direction. Then, a frequency chart was created as the height (or the length in the Z'-axis direction). Based on this frequency chart, the vibration group is divided into a vibration group whose resonance frequency is not affected by the length in the X-axis direction (or the length in the Z'-axis direction) and a vibration group that is greatly influenced by these vibration modes. It was observed in detail using the needle method. This observation method uses inharmonic overtons that occur on the high frequency side of the main vibration, and higher-order contour vibrations (bending vibration,
It is suitable for observing longitudinal vibration, surface sliding vibration, etc.), and in conjunction with the frequency chart, gives guidance on how to avoid coupling between main vibration and sub-vibration and design a good small AT-cut crystal resonator. ing.

In 1963, Spencer et al. Developed a Lang method using transmission X-ray diffraction to determine the vibration mode of a vibrating element having an electrode film attached to an AT-cut substrate. Vibration (Inharmonic Overton)
Was observed in detail. This observation method makes it easy to observe the vibration mode with multiple antinodes and nodes in the X-axis direction and Z 'direction that could not be observed because the resolution was insufficient with the probe method, and to suppress a specific vibration mode Electrode design became possible. Sekimoto et al., "Two-dimension
al analysisi of thickness-shear and flexural vibra
tions in rectangular AT-cut quartz plates using a
one-dimensional finite element method ”(44th FCS, p
In 358-p362, '90), when both the thickness of the AT-cut substrate and the length in the X-axis direction were constant and only the length of the Z'-axis was changed, not only the higher-order contour vibration but also bending Using a finite element method to obtain a frequency chart that takes vibration into account,
This is compared with the experimental value. Although high-order plane-slip vibration and longitudinal vibration are not considered in this calculation, the calculated frequency chart and the experimental frequency chart are in good agreement, and are used in the design of small AT-cut quartz resonators. .

FIGS. 4A and 4B show an example of the structure of a conventional AT-cut quartz crystal resonator designed based on the suggestions of the prior art. FIG. 4A is a plan view, and FIG. FIG. Electrodes 12 are located approximately at the center of both main surfaces of crystal substrate 11.
a, 12b (hereinafter, referred to as base electrodes), and then lead electrodes 13a, 13b extending from the base electrodes 12a, 12b, respectively.
And terminals of a holder (not shown) are fixed using a conductive adhesive or the like. As is well known, the precision of the frequency required for the crystal unit is on the order of ppm, but it is difficult to obtain a desired frequency because the thickness of the base electrode varies due to manufacturing errors. Therefore, fine adjustment of the frequency is performed by depositing a small amount of metal from one surface (or both surfaces) of the crystal unit via a mask for fine frequency adjustment by means of evaporation or the like, that is, attaching the fine adjustment electrode 14. It is common to do. In this case, an automatic frequency adjuster that reduces the frequency while monitoring the frequency of the crystal vibrating element using a measuring instrument and adjusts the frequency to a predetermined frequency is generally used.

FIG. 4 (b) shows the vibration displacement distribution of the crystal resonator. The displacement distribution after the base electrode is deposited is a distribution shown by a solid curve α. When the frequency fine-tuning electrode 14 is attached to adjust the frequency, the energy confinement effect becomes larger than that in the base vapor deposition state, and the distribution becomes as shown by the dashed curve β (both curves α and β have the maximum value of the displacement distribution). Is standardized). This is because the mass effect at the center of the electrode increases because the electrode pattern having a diameter smaller than the diameter of the base electrode is used so that the fine adjustment electrode 14 does not protrude from the area of the base electrode 12a. When the energy confinement effect increases as in the curve β, the vibration energy leaking from the holding unit decreases, so that the equivalent resistance R1 of the oscillator decreases, that is, the Q value of the oscillator increases.

[0006] Connect the load capacitance C _L in series to the crystal oscillator, when changing the container volume, as shown in FIG. 5 (a), the secondary vibration to the main vibration in a volume value (frequency f ₁₎ (F ₂ ) may be coupled, and the frequency of the main vibration fluctuates slightly near the frequency f ₂ of the sub-vibration, or the frequency jumps depending on the degree of coupling. As is well known, this variation in frequency is called the frequency variation due to the CI dip because it is proportional to the variation rate ΔR of the equivalent resistance (CI) shown in FIG. Here, the variation rate ΔR of the equivalent resistance indicates a rate at which the energy of the main vibration leaks to the sub-vibration when the sub-vibration is coupled to the main vibration, and as a result, the equivalent resistance of the main vibration becomes apparently large. . Here, the variation rate ΔR of the equivalent resistance is expressed by the following equation. ^{_{ΔR = QQ n k 2 (1}} ) where, Q is the Q value of the principal vibration, Q _n is the secondary vibration Q value, k represents the degree of coupling primary vibration and secondary vibration.

[0007]

However, in the above-mentioned conventional frequency fine-tuning method, when a metal is deposited to adjust the frequency of the quartz oscillator to a predetermined frequency, the energy confinement effect becomes large. In this case, a deviation occurs from that suggested by the above, and the Q value of the main vibration increases. As the Q value of the main vibration increases, the variation rate ΔR of the equivalent resistance of the main vibration increases according to the above equation (1). As a result, there is a problem that the amount of frequency fluctuation increases when the sub-vibration is coupled. SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and has as its object to provide a crystal resonator having a small amount of frequency fluctuation.

[0008]

According to a first aspect of the present invention, there is provided a piezoelectric vibrator according to the present invention. In a piezoelectric vibrator having an electrode, a second electrode for fine-tuning the frequency is attached on the electrode, and the frequency is adjusted to a predetermined frequency. In the piezoelectric vibrator, the second electrode is peripherally formed except for a central portion of the first electrode. A piezoelectric vibrator attached to a portion. Claim 2
The described invention comprises a first electrode having a predetermined size substantially at the center of both main surfaces of the piezoelectric substrate, and removing the mass from the electrode to adjust the frequency to a predetermined frequency. A piezoelectric vibrator characterized in that mass removal of an electrode is removed from a central portion except for a peripheral portion of the electrode.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the drawings. 1A and 1B are diagrams showing a configuration of a crystal resonator according to the present invention. FIG. 1A is a plan view, and FIG. 1B is a cross-sectional view along AA. Electrodes 2a and 2b are attached to almost the center of both main surfaces of quartz substrate 1, and then held in a holder (not shown). Lead electrodes 3a and 3b of base electrodes 2a and 2b and terminals of the holder are electrically conductive adhesive. Fix using A small amount of metal is vapor-deposited from one surface (or both surfaces) of the crystal vibrating element by means such as vapor deposition through a mask for fine frequency adjustment, and the frequency is adjusted to a predetermined frequency.

The quartz resonator according to the present invention is characterized in that a metal or the like is attached to the periphery except for the center of the base electrode 2a, and the frequency is reduced by a mass effect to adjust the frequency to a predetermined frequency. Therefore, the vibration displacement distribution is different from the conventional distribution. That is, the displacement distribution after attaching the base electrodes 2a and 2b is as shown by a curve α shown by a solid line.
When the electrode 4 for fine frequency adjustment according to the present invention is attached, the vibration displacement distribution has a broader skirt than the curve α, and the energy confinement effect is slightly reduced. Therefore, the equivalent resistance R1 of the crystal resonator is slightly larger than that of the conventional one,
The value will be slightly smaller. As a result, when varying the capacitive connecting the load capacitance C _L in series to the crystal oscillator, or the like when changing the ambient temperature of the crystal oscillator, even higher contour vibration is attached to the main vibration , The Q value of the main vibration of the equation (1) becomes smaller, so that the variation rate ΔR of the equivalent resistance becomes smaller,
Therefore, the frequency fluctuation is reduced.

FIG. 2 shows a modified embodiment of the present invention.
FIG. 1 is a plan view, and FIG. 2B is a cross-sectional view taken along the line AA, which is an example in which the present invention is applied to a surface-mount type crystal unit. A quartz substrate 1 is processed into a strip shape, and a rectangular base electrode 2
A and 2b are attached by a method such as vapor deposition and the like, are housed in a ceramic package (not shown), and are fixed by using a conductive adhesive with the lead electrodes 3a and 3b and terminal electrodes provided on the peripheral step portion of the package. A small amount of metal is deposited from the open surface of the ceramic package through a fine adjustment mask. At this time, vapor deposition is performed using a mask so that the electrode 4 for frequency adjustment is formed in the peripheral portion except for the central portion of the base electrode 2a.

3A and 3B show another modified embodiment of the present invention. FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view taken along the line A--A of FIG. This is an example in which is applied. Since the electrode 5 for frequency adjustment is formed inside the outer periphery of the electrode base electrode 2a as compared with FIG.
Can be prevented from protruding outside of the region of the base electrode 2a when adhering.

In the above frequency adjustment, an electrode 4 for fine frequency adjustment is attached on the base electrode 2a by using a technique such as vapor deposition.
Although the method of adjusting the frequency by the mass effect has been described, only the central portion of the base electrode 2a is slightly cut with an electron beam or the like,
The object of the present invention can also be achieved by adjusting the frequency.

[0014]

According to the present invention, as described above, even when the main vibration and the sub-vibration of the crystal unit are coupled by the load capacitance or by the temperature fluctuation, the frequency fluctuation due to the coupling is reduced. Therefore, if the crystal resonator according to the present invention is used in a wireless communication device or the like, an effect of exhibiting excellent characteristics with little frequency fluctuation with respect to a temperature change of a use environment can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a crystal resonator according to the present invention;
(A) is a plan view, (b) is a diagram showing a sectional view and a displacement distribution.

2A is a plan view of a modified embodiment of the present invention, FIG.
(B) is a figure which shows sectional drawing.

3A is a plan view of another modified embodiment of the present invention, FIG.
(B) is a figure which shows sectional drawing.

4A and 4B are diagrams showing a configuration of a conventional vibrator, in which FIG. 4A is a plan view, and FIG. 4B is a diagram showing a sectional view and a displacement distribution.

5A is a diagram illustrating a state in which the frequency of a main vibration fluctuates due to coupling of a sub-vibration, and FIG. 5B is a diagram illustrating a fluctuation rate ΔR of an equivalent resistance value.

[Explanation of symbols]

 1. Piezoelectric substrate 2a, 2b Base electrode 3a, 3b Lead electrode 4, 5, Electrode for frequency adjustment α, β: Displacement distribution of vibration

Claims (3)

[Claims] An excitation electrode having a predetermined area is disposed on both main surfaces of a piezoelectric substrate so as to face each other via a piezoelectric substrate, and an electrode thickness of at least one central portion of the excitation electrode is set to that of a peripheral portion. A piezoelectric vibrator characterized by being thinner. 2. An excitation electrode having a predetermined area is formed on both main surfaces of a piezoelectric substrate so as to face each other via a piezoelectric substrate, and a central portion of at least one of the excitation electrodes is removed to remove the excitation electrode. A piezoelectric vibrator characterized by adjusting to a frequency. 3. An excitation electrode having a predetermined area is formed on both main surfaces of the piezoelectric substrate so as to face each other via the piezoelectric substrate, and an adjustment electrode is attached to at least one peripheral portion of the excitation electrode. And adjusting the frequency to a predetermined frequency.