JPH0128530B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrode structure of a tuning fork type crystal resonator. In particular, the present invention relates to a tuning fork-type bent torsional crystal resonator in which a bending mode and a torsion mode are combined as vibration modes. The object of the invention is a torsional mode crystal. The goal is to reduce impedance (called CI). Another object of the present invention is to stably provide a tuning fork type bent torsional crystal resonator having excellent low frequency temperature characteristics.

Crystal resonators used in watches, especially tuning fork-shaped bent crystal resonators, are now fully in use. However, just because a large number of vibrators are currently in use does not mean that there are no problems, and this vibrator also has various drawbacks. Among these, the major drawback was that the frequency-temperature characteristics were inadequate over a wide temperature range, which placed a limit on the accuracy of the clock. Therefore,
Recently, using two of these oscillators, furthermore,
Although a method with improved frequency-temperature characteristics has been proposed, this method has the disadvantage that it is difficult to combine two oscillators, and at the same time, it is expensive because it uses two crystals. Furthermore, there is an AT-cut crystal oscillator that is a single crystal oscillator and has excellent frequency-temperature characteristics, but the frequency of this oscillator is high in the MHz band, and it consumes a lot of current for watches, so it cannot be used at present. This is the current situation. Therefore, there was a demand for a single crystal resonator with low frequency and excellent frequency-temperature characteristics.Recently, bent torsional crystal resonators with low frequency and excellent frequency-temperature characteristics have been developed. Proposed. However, nothing is known about its electrical characteristics, ie, the change in frequency temperature characteristics depending on the CI value of the bending mode, which is the main vibration, and the torsion mode, which is the secondary vibration. Therefore, the present invention has been developed so that the CI value of the bending mode, which is the main vibration, does not deteriorate.
In order to stably obtain a crystal resonator with excellent frequency-temperature characteristics, it was found that it is very important to improve the CI value of the torsional mode, which is the secondary vibration. below,
The present invention will be explained along with the drawings.

Figure 1 shows the thickness t of the bent torsional crystal resonator of the present invention.
Flexural mode vibration F _M and torsional mode when changing
FIG. 3 is a diagram showing a bonding state with _TM . If there is no coupling between both modes, it is known that the frequency of torsional mode vibration T _M changes approximately along a straight line with a slope with respect to thickness t, and that bending mode vibration F _M changes approximately with respect to thickness t. Since the frequency is almost unrelated to , both vibration modes should have an intersection point I when the thickness t is changed. but,
In reality, since coupling occurs between both modes, the situation will be slightly different. Now, to explain the oscillators with thicknesses t _{1 and} t ₂ , if the resonance frequency of the torsional mode of the t ₁ oscillator is ₁ and the resonance frequency of the bending mode is ₂ , the difference △ ₁ is given by △ ₁ = ₂ − _1. It will be done. On the other hand, if the resonant frequency of torsional mode vibration of a vibrator with thickness t _{2 is 3} and the resonant frequency of bending mode is ₄ , the difference △ ₃ is given by △ ₃ = ₄ - ₃ . What is understood here is that bonding occurs at different thicknesses. In other words, in the t ₂ oscillator, the frequency difference △ between bending mode vibration and torsional mode vibration is t ₁
This means that even if it is larger than the oscillator, it will couple (△ ₃ > △ ₁ ). This means that the CI values of torsional mode vibration are different for each. In other words, the smaller the CI value of torsional vibration, the more likely it is to cause coupling, and in Figure 1, CI1>
CI2 is involved. The larger the frequency difference between the bending mode and the torsion mode, the less the reactance characteristics of the main vibration, the bending vibration, will deteriorate, so the CI of the main vibration
The value can be reduced. In a vibrator coupled in this way, how can the CI of torsional mode, which is secondary vibration, occur?
It can be seen that reducing the value is the key point in resonator development. Figure 2 shows torsional vibration, which is secondary vibration.
An example of the electrode structure of the present invention for lowering the CI value is shown. The X, Y, and Z axes represent the electrical, mechanical, and optical axes of the crystal, respectively, and the rotational axis is θ.
The view when rotated is shown in FIG.
The Y′ and Z′ axes are the new axes after rotation. The tuning fork crystal 1 has tuning fork arms 1a and 1b, with an electrode a on the top surface of the tuning fork arm 1a, an electrode c (not shown) on the bottom surface, an electrode b on one side, and an electrode B on the other side. Electrodes d (not shown) are arranged respectively. Similarly, electrodes e, f, g, and h (g and h are not shown) are arranged on the upper and lower surfaces and side surfaces of the other tuning fork arm 1b. FIG. 3 shows a cross-sectional view of the tuning fork arm of the tuning fork crystal resonator shown in FIG. 2, taken approximately at the center. A and B indicate electrode terminals. Now, if we assume that a positive voltage is applied to electrode terminal A and a negative voltage is applied to electrode terminal B, the electric field will act as shown by the arrows.To simplify the explanation, we will explain the tuning fork arm on the left. The electric field between cd and the electric field between ad and cb show electric fields in opposite directions with respect to the X-axis direction component. Therefore, if an elongation strain occurs between AB and CB, a contraction strain will occur between AD and CD. Therefore, the tuning fork arm undergoes flexion. Furthermore, since the electrode a on the top surface and the electrode c on the bottom surface of the present invention are arranged asymmetrically with respect to the thickness, the amount of strain differs in each part of the vibrator. In other words, the absolute value of the distortion between AB is greater than the absolute value of the distortion between AD and CB, and the absolute value of the distortion between CD is also greater than the absolute value of the distortion between AD and CB. growing. To be more specific, ab
When there is an elongation strain between CDs, there will be a lot of contraction strain between CDs, so this displacement will not be within the horizontal plane of the tuning fork arm, but will be displaced in a direction slightly tilted from the horizontal plane. . Therefore, as mentioned above,
A torsional vibration mode combined with a bending mode vibration can be induced. In exactly the same way, distortion can be caused on the other tuning fork arm. Furthermore, by applying an alternating current voltage between electrode terminals A and B, it is possible to sustain the vibration of the tuning fork type bent torsion crystal resonator. Figure 4 is similar to Figures 2 and 3.
FIG. 2 is a perspective view showing the vibration state of the tuning fork type bent torsional crystal resonator of the present invention when the electrodes shown in the figure are arranged. 2 indicates bending mode vibration, 3 indicates torsion mode vibration, and 4 indicates bending-torsion mode vibration in which vibration 2 and vibration 3 are combined.

As described above, the present invention allows the electrode arrangement on the upper and lower surfaces of the tuning fork arm of a tuning fork crystal resonator to be adjusted according to the thickness.
By making it asymmetrical, torsional vibration is more likely to occur. In other words, it has become possible to lower the CI value. As a result, coupling between the bending mode vibration, which is the main vibration, and the torsional mode vibration, which is the secondary vibration, has become more likely to occur.In other words, even if the frequency difference between the main vibration and the secondary vibration is large, coupling occurs. Therefore, it is possible to stably provide a tuning fork type bent torsional crystal resonator with excellent frequency temperature characteristics at low frequencies. At the same time, one crystal oscillator can perform frequency compensation over a wide temperature range, making it inexpensive. In the embodiment of the present invention, the electrodes on the top and bottom surfaces are arranged on the outside and the bottom on the inside, but the same effect can be obtained even if the top electrode is placed on the inside and the bottom electrode is placed on the outside.

[Brief explanation of drawings]

Figure 1 shows the thickness t of the bent torsional crystal resonator of the present invention.
FIG. 2 is a perspective view showing an embodiment of the electrode structure of the present invention for lowering the CI value of torsional vibration, which is secondary vibration. The figure is a sectional view of the tuning fork type crystal resonator shown in FIG. 2, and FIG. 4 is a perspective view showing the vibration direction of the tuning fork type bent torsional crystal resonator of the present invention. 1... Tuning fork type crystal, 1a, 1b... Tuning fork arm,
a, e...Top electrode, c, g...Bottom electrode, b,
d, f, h...side electrodes.

Claims (1)

[Claims] 1. In a crystal resonator formed in a tuning fork shape and having a mixture of bending mode and torsional mode, one electrode is provided on the top, bottom, and both sides of each tuning fork arm of the tuning fork type crystal resonator. The electrodes on the upper surface and the electrodes on the lower surface arranged on each of the above tuning fork arms are arranged at asymmetrical positions across the thickness in the upper and lower directions, and each electrode is connected to one tuning fork arm. The polarity of the potential applied to the upper and lower electrodes and the electrodes placed on both sides of the other tuning fork arm, and the polarity of the potential applied to the upper and lower electrodes of the other tuning fork arm and the electrodes placed on both sides of one tuning fork arm. 1. An electrode structure for a tuning fork crystal resonator, characterized in that the polarities of potentials applied to the first and second electrodes are different from each other.