JP2813996B2 - 3rd overtone AT-cut crystal unit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a tertiary overtone piezoelectric vibrator that performs thickness shear vibration.

[Prior Art and Problems to Be Solved] A conventional piezoelectric vibrator that performs thickness-shear vibration has a configuration suitable for main vibration drive by forming circular drive electrodes on both sides of a circular crystal resonator. However, this oscillator has
It has many sub-vibrations in addition to the main vibration, and there is a problem that if the main vibration causes a coupling with a higher-order sub-vibration during the vibration, an abnormal frequency phenomenon will occur particularly in the frequency temperature characteristic. Therefore, in order to avoid particularly coupling with the auxiliary vibration of the contour system, proposals have been made with emphasis on the design of the shape and dimensions of the circular drive electrode (for example, Japanese Patent Publication Nos. 60-13608 and 63-63). -40492).

However, this vibrator has a problem that, in addition to the coupling with the sub-vibration as described above, the main vibration is coupled with the thickness-shear-type sub-vibration accompanying the higher-order harmonic vibration. Therefore, the applicant of the present application considered those measures in consideration of
It has been previously proposed by Japanese Patent No. 38764. This is a countermeasure against coupling with higher-order sub-vibrations, and on the circular drive electrode, furthermore, an electrode for frequency adjustment is provided in an eyeglass shape, and an attempt was made to solve the problem by using the load mass effect. Things.

However, even in the case where the load mass in the form of glasses is provided, an error occurs in the position of the load mass due to a shift of the position of the mask for forming the load mass, or the amount of adjustment is small and the load mass effect is small. There is such a problem.

[Object of the Invention] An object of the present invention is to eliminate occurrence of an abnormal frequency phenomenon in a tertiary overtone piezoelectric vibrator.

Means for Achieving the Object In order to achieve the above object, a tertiary overtone piezoelectric vibrator according to the present invention is provided on both principal surfaces of a circular piezoelectric element that performs thickness-shear vibration, and is horizontally elongated in the Z′-axis direction. When the diameter of the piezoelectric element is D, the length of the drive electrode in the Z′-axis direction is L, and the length in the X-axis direction is W, the dimensions of each drive electrode are provided.
L and W are formed in the range of W <D / 3, 0.5D ≦ L ≦ 2D / 3,
The center of the main surface of the piezoelectric element coincides with the center of each drive electrode, and each drive electrode has a line symmetry with respect to the center line in the Z′-axis direction and the center line in the X-axis direction.

[Example] The abnormal frequency phenomenon has a completely different cause from the conventional jump phenomenon (a phenomenon in which the main vibration of the fundamental mode of thickness-shear is drawn into the sub-vibration existing relatively close thereto). And is closely related to a high-frequency vibration (nearly three times the resonance frequency of the fundamental vibration) existing near a frequency of n (odd number equal to or more than 3) which is far from the resonance frequency of the fundamental vibration, It occurs suddenly when 1 / n of the frequency of the high-frequency vibration coincides with the resonance frequency of the basic vibration due to the fluctuation of the ambient temperature or the load capacity. For example, when used in the fundamental vibration, the coupling state is often determined by the relationship between this fundamental wave and the spurious vibration of the second-order overtone, or when used in the third-order overtone, by the relationship with the spurious vibration of the ninth overtone. And an abnormal frequency phenomenon occurs.

FIG. 6 shows a resonance characteristic when a conventional 6 mm-diameter crystal oscillator having a circular drive electrode is used in the third overtone, and the frequency of the third overtone (F3) is 23.64495. MHz, three times the frequency is 70.93
Although it is 485 MHz, in the vicinity of the triple frequency, a spurious vibration (F9S1) of the ninth overtone (F9) exists as a vibration of frequency 70.92996 MHz, and as another spurious vibration (F9S2), A vibration with a frequency of 70.94705 MHz exists. 70.93485MHz, three times the frequency of the third order overtone (F3), and 70, the frequency of spurious vibration (F9S1)
Since the distance from 92996 MHz is only -4.89 KHz, when this piezoelectric vibrator is used in the third overtone (F3), the ninth overtone (F9 ) And spurious vibration (F9S1). This is observed as a frequency abnormal phenomenon as seen in a circled portion in the frequency temperature characteristic diagram shown in FIG.

The present invention, in order to avoid such a frequency abnormal phenomenon,
Each vibration mode was analyzed, and it was configured to avoid coupling with higher-order spurious vibrations by using the mass loading effect of the electrode film.

One embodiment of the piezoelectric vibrator of the present invention shown in FIGS. 1 and 2 uses a circular crystal vibrator 1 having a diameter of 6 mm as a piezoelectric element, and has horizontally long drive electrodes 2 formed on both main surfaces thereof. . The crystal unit 1 has a certain angle in the Y-axis direction from the Z-axis, which is the original coordinate axis, that is, about 3 ° at which the frequency temperature coefficient becomes zero.
An AT-cut crystal unit cut along a plane inclined by 5.4 ° is used. The quartz plate cut from the quartz at this angle has X, Y 'and Z' in the respective axial directions shown in FIGS. From the quartz plate having such a cutting angle, the quartz resonator 1 of the present invention having a circular shape having a diameter D is formed.

The drive electrodes 2 formed on both main surfaces of the crystal unit 1
As shown in FIG. 3, when the length in the Z′-axis direction is L and the length in the X-axis direction is W, as described in detail later, W <D /
3 and 0.5D ≦ L ≦ 2D / 3
Is set so that the center of both main surfaces coincides with the center of the drive electrode 2, and both drive electrodes 2 are line-symmetric with respect to the center line in the Z′-axis direction and the center line in the X-axis direction, respectively. It is formed in. An extraction electrode 2a is formed from the drive electrode 2 toward the outer periphery.

In the present invention, the crystal unit 1 is used for the third overtone (F3).
Along with 3), higher harmonic vibration and its spurious vibration are also generated. An ellipse 3 shown by a chain line in FIG. 1 (a) shows a charge concentration region of the third overtone (F3), and although not shown, charges are concentrated at the center.

The three ellipses 4a, 4b, 4c shown by chain lines in FIG.
This is the charge concentration region of the spurious vibration (F9S1) of the ninth overtone (F9) generated by the third overtone (F3), and the charge is shown by the charge distribution curves in FIGS. 1 (b) and (c). Thus, it can be seen that the charges having different polarities are concentrated in the regions 4b, 4c on both sides of the region 4a on the Z 'axis on the X axis and the Z' axis. . With respect to this spurious vibration (F9S1), since the drive electrode 2 is provided on almost the entire surface of the charge concentration regions 4a, 4b, 4c,
A mass loading effect is provided by the electrode film, and the frequency can be shifted to the minus side.

Further, three ellipses 5a, 5b, indicated by chain lines in FIG.
5c is a charge concentration region of another spurious vibration (F9S2) of the ninth overtone (F9) caused by the third overtone (F3), and the charge is in FIG. 2 (b) and FIG. 2 (c). As shown in the charge distribution curves, on the X axis and the Z ′ axis, the charges are concentrated in the central region 5a, and the charges having different polarities are concentrated on the regions 5b, 5c on both sides of the region 5a on the X axis. You can see that there is. With respect to this spurious vibration (F9S2), since the drive electrode 2 is provided only in the central region 5a of the charge concentration regions 5a, 5b, 5c, the mass loading effect by the electrode film is reduced, and the frequency is shifted to the plus side. Can be moved.

FIG. 4 shows the resonance characteristics when the circular quartz oscillator 1 having the drive electrode 2 horizontally long in the Z'-axis direction of the present invention is used in the third overtone, and the third overtone (F
The frequency of 3) is 23.64720MHz, and the triple frequency is 70.9
4160 MHz. The spurious vibration (F9S1) of the ninth overtone (F9) is near the frequency three times this frequency.
70.92510MHz, and yet another spurious vibration (F9S
2) exists at a frequency of 70.97407 MHz. The frequency of 70.94160 MHz, which is three times the third-order overtone (F3), and the frequency 70.92510 MHz of the spurious vibration (F9S1) are apart from each other by -16.5 KHz, and the spurious vibration (F9S1) shown in FIG.
Compared to the case where the frequency is only 4.89 KHz apart, the distance has moved greatly to the-side, and the coupling with the third overtone (F3) can be sufficiently avoided. In addition, spurious vibration (F9S
Also in the case of 2), in the case of FIG. 4, the distance is +32.47 KHz, but in the case of FIG. 6, the distance is only +12.2 KHz. No coupling occurs with the third overtone (F3). As a result, as shown in the frequency temperature characteristic diagram of FIG.
The frequency abnormal phenomenon as shown in the figure does not occur.

As described above, the driving electrode 2 gives a mass loading effect to the higher-order spurious vibration (F9S1) to shift the frequency to the negative side, and to the other higher-order spurious vibration (F9S2). Since the shape is set so as to reduce the mass loading effect and shift the frequency to the + side, it is desirable to increase L so as to cover all the charge concentration regions 4a, 4b and 4c. However, since the outer peripheral portion of the piezoelectric element 1 is held by the holding member, it is necessary to leave a certain space in the outer peripheral portion so as not to hinder the holding. Therefore, L ≦ 2D / 3 is left as the space remaining for D / 3. However, if L is too small, the charge concentration regions 4a, 4b, 4c cannot be covered, so
D / 2 ≦ L. On the other hand, it is desirable that W not cover at least the charge concentration regions 5b and 5c so as not to give much mass loading effect, and therefore W <D / 3 is set. . L and W may be determined in a well-balanced manner under such considerations. Therefore, the drive electrode 2 only needs to be horizontally long in the Z′-axis direction, and may have an elliptical shape, a rectangular shape, or the like.

[Effect] As described above, in the third-order overtone AT-cut crystal resonator according to the present invention, 1 / n of the high-order spurious vibration existing near the frequency n times the fundamental vibration matches the resonance frequency of the fundamental vibration. In order to eliminate the frequency abnormal phenomenon that occurs suddenly when doing, the mass electrode effect of the electrode film is used, and the shape of the drive electrode is made horizontally long in the axial direction as described in the claims. As a result, the frequency of the spurious vibration of the ninth overtone is improved so as to be away from three times the frequency of the tertiary overtone as the main vibration, and the above-described frequency abnormal phenomenon occurs over a wide temperature range. Generation can be reliably removed or suppressed. Therefore, the operation of the thickness shear vibration is stabilized, and the output frequency thereof becomes extremely high precision. In addition, since the shape of the drive electrode is simple, manufacture is extremely easy, and a third-order overtone AT-cut crystal resonator having uniform quality can be provided at low cost.

[Brief description of the drawings]

FIG. 1 (a) is a front view of a piezoelectric vibrator showing one embodiment of the present invention, and shows surface charge distributions in spurious vibrations of a third-order overtone and a ninth-order overtone.
FIGS. 2 (b) and 2 (c) are surface charge distribution curves for the above-described spurious vibration, and FIG. 2 (a) is a front view of the same.
2 (b) and 2 (c) show surface charge distribution curves in the above-described spurious vibration, and FIG. 3 is a front view showing a drive electrode. FIG. 4 is a diagram showing the resonance characteristics of the tertiary overtone and the ninth overtone in the piezoelectric vibrator of the present invention, FIG. 5 is a diagram showing the frequency-temperature characteristics of the piezoelectric vibrator of the present invention, and FIG. FIG. 7 is a diagram showing resonance characteristics of a third-order overtone and a ninth-order overtone in a conventional piezoelectric vibrator having electrodes. FIG. 1 .... quartz plate (crystal oscillator) 2 .... drive electrode.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Isamu Hoshino 4-1-1, Taihei, Sumida-ku, Tokyo Inside Seikosha Co., Ltd. (56) References JP-A-63-284920 (JP, A) JP-A-53 -36494 (JP, A) JP-A-62-109419 (JP, A)

Claims (1)

(57) [Claims] 1. An AT-cut circular quartz plate which performs thickness-shear vibration is provided with drive electrodes which are horizontally long in the Z'-axis direction on both principal surfaces, wherein the quartz plate has a diameter of D, and the drive electrode has a Z'-axis. When the length in the X-axis direction is L and the length in the X-axis direction is W, the dimensions L and W of the respective drive electrodes are in the range of W <D / 3, 0.5D ≦ L ≦ 2D / 3, and The center of the main surface of the plate coincides with each of the drive electrodes, and each of the drive electrodes has a shape symmetric with respect to the center line in the Z′-axis direction and the center line in the X-axis direction. 3rd overtone AT-cut crystal resonator.