JPS6246091B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrode structure of a tuning fork type crystal resonator.

The main object of the present invention is to provide a tuning fork type crystal resonator that uses the second harmonic of the bending mode. Such a tuning fork type crystal oscillator realizes a small quartz crystal oscillator used in, for example, an electronic wristwatch. In addition, another object of the present invention is to
The goal is to achieve higher precision in electronic wristwatches. Conventionally, a tuning fork type crystal oscillator as shown in FIG. 1 has been used as a oscillator for an electronic wristwatch. Figure 1A
indicates a cutting angle, which is formed into a tuning fork shape by etching a quartz plate 1 obtained by rotating a Z plate by 0 degrees to 15 degrees around the X axis. Figure 1B is a plan view showing the electrolytic structure, and Figure 1C is the X-
FIG. 3 is a sectional view taken along the X' line. Currently, the mainstream is a vibrator with a frequency of 32 kilohertz, but when this vibrator is used in a wristwatch, the second
In order to obtain a desired oscillation frequency using an oscillation circuit using CMOS 3 as shown in the figure, it is necessary to adjust the resonant frequency of the vibrator 2 itself quite precisely in advance. This is because, in the case of small vibrators for wristwatches, the range in which the frequency can be adjusted by changing the load capacity on the circuit side is very narrow, approximately 30 × 10 ^-6 . This frequency adjustment work is extremely troublesome, and furthermore, a decrease in yield cannot be avoided. Recently, attempts have been made to divide the oscillation frequency to obtain a clock signal with a desired period by changing the division ratio of the frequency divider circuit. In this case, the resolution of 1 hezurtz is as large as 30×10 ^-6 , and even if logical scaling measures are used, the above-mentioned drawbacks could not be solved. Therefore, in order to increase the effect using logical speeding and slowing means, it is sufficient to increase the frequency, but the resonant frequency f of the tuning fork type vibrator is determined by the length of the vibrating arm being l and the width being W. Then, it is known that f∝W/l _2. Therefore, in order to increase the frequency without increasing the size, it is necessary to shorten the length l. For example, if the length of the vibrating arm is halved, the frequency will increase four times, but when crystal is etched, etching residue 4a as shown in FIG. 3 cannot be avoided. This etching residue is very thin, and stress concentration is unavoidable, especially near the crotch. Therefore, if the length l of the vibrating arm is shortened, the proportion of remaining etching will increase, and long-term reliability will inevitably deteriorate.

Furthermore, in recent years, attempts have been made to improve the frequency-temperature characteristics of wristwatches by using two tuning-fork crystal units. One of them is to connect two vibrators 5 and 6 in parallel as shown in FIG. 4B to obtain a frequency-temperature characteristic as shown by curve 7 in FIG. 4A. Curves 5a and 6a are frequency-temperature characteristics of single vibrators 5 and 6, respectively. Here, the peak temperature T _OH on the high temperature side is 40
℃ is the upper limit, and in order to obtain good temperature characteristics over a wider range, it is necessary to increase T _OH . Another method, as shown in FIG. 5B, is to connect the two oscillators 89 to separate oscillation circuits 13 and 14, and use a subtraction circuit to calculate the difference △f between the respective frequencies f ₁ ' and f ₂ . 1
5, and from △f in the arithmetic circuit 16, K×
(△f) Creates ² . At this time, K×(Δf) ² is selected so that K has a temperature characteristic 11 that is symmetrical to the frequency-temperature characteristic 8a of the vibrator 8 shown in FIG. 5A. Then, the frequency f ₁ and K×(△f) ² are divided by the frequency dividing circuit 17
are added logically, and the output signal has little fluctuation in period with respect to temperature changes. That is, a frequency-temperature characteristic equivalently shown in curve A 12 in FIG. 5 is obtained. However, since logical processing is performed in this case as well, the high resolution of 1 hertz as described above has been a considerable drawback in achieving high precision. Furthermore, a decrease in Q value is unavoidable with miniaturization, and in the resonator shown in Figure 1, Q is approximately 100,000, so it is desirable to increase Q in order to achieve high precision. It was rare.

Therefore, in order to solve the above-mentioned drawbacks, the present invention
The purpose is to obtain a high resonant frequency, a high Q value, and a high peak temperature by using a vibrator that has almost the same shape and size as the current vibrator.

The present invention will be described below with reference to the drawings. An embodiment of the present invention is shown in FIGS. 6A and 6B. 6th
Diagram A shows one side (referred to here as the surface),
FIG. 6B shows the other side (here referred to as the back side). Further, assuming that the length of the vibrating arm is l, the vibrating arm is divided into a tip side and a base side at a portion of 0.6l to 0.85l from the tip (hereinafter referred to as an electrical node). That is, regarding one vibrating arm 18a, 18a-1 is the tip side, 18a-2 is the base side, and the other vibrating arm 1
Regarding 8b, 18b-1 is on the tip side, 18b-
2 is the base side. First, to explain the surface, a peripheral electrode 19a on the tip side of one vibrating arm 18a is connected by an electrode 19aa arranged at the tip along the width direction, and a central electrode 19b on the base side.
and is connected by an electrode 19ab arranged at the electrical node. Further, the peripheral electrode 19d on the base side is connected by an electrode 19dd arranged at the base along the width direction, and is further connected to the center electrode 19c on the tip side.
It is connected by an electrode 19cd placed at the electrical node. Regarding the other vibrating arm 18b,
The peripheral electrode 19e on the tip side is connected by an electrode 19ee arranged at the tip along the width direction, and is further connected to a central electrode 19f on the base side by an electrode 19ef arranged at the electrical node. Furthermore, the inner electrode among the peripheral electrodes h on the base side is not connected anywhere within the surface, and the outer electrode is connected to the center electrode 19 on the tip side.
g and is connected by 19gh located at the electrical node. The base-side peripheral electrode 19d of the vibrating arm 18a and the base-side central electrode 19 of the vibrating arm 18b.
f is connected by an electrode 19df arranged at the base.Next, to explain the back side, one vibrating arm 18
The peripheral electrode 19m on the tip side of a is connected to the electrode 19mm arranged at the tip along the width direction, and further connected to the central electrode 19n on the base side and the electrode 19mn arranged at the electrical node. Connected. Moreover, the inner electrode of the peripheral electrode 19p on the base side is not connected anywhere, and the outer electrode is connected to the center electrode 19 on the tip side by the electrode 19p arranged at the electrical node. The other vibrating arm 18
Regarding b, the peripheral electrode 19i on the tip side is
It is connected by an electrode 19ii arranged at the tip along the width direction, and further connected by a central electrode 19i on the base side.
and are connected by an electrode 19ij placed at the electrical node. The peripheral electrode 19l on the base side is connected by an electrode 19ll arranged at the base along the width direction, and further connected to the center electrode 19k at the tip side by an electrode 19kl arranged at the electrical node. Ru. And the center electrode 19 on the base side of the vibrating arm 18a
n and the proximal peripheral electrode 19l of the vibrating arm 18b are connected by an electrode 19ln arranged at the base.
and 19m are connected on the front and back by electrodes 19am arranged on the sides. Similarly, the other vibrating arm 18
The front and back peripheral electrodes 19e and 19i on the tip side of b are connected to each other by an electrode 19ei arranged on the side surface. At this time, 19am and 19ei are placed on the left and right sides, respectively, when viewed from the front.
This is a diagram placed on the right side, but it could be placed on the right or left side. Furthermore, the inner electrodes of the inner electrodes 19p of the base-side peripheral electrodes 19d of the vibrating arm 18a are connected by electrodes 19dp-1 arranged on the side surfaces. This side electrode 19dp-1 connects the inner electrode of the base side peripheral electrode 19p on the back surface to another electrode for the first time. Similarly, vibrating arm 18b
The inner electrode of the base-side peripheral electrode 19h and the inner electrode of 19l are connected by an electrode 19hl-1 arranged on the side surface. Further, the outer electrode of the base-side peripheral electrode 19d of the vibrating arm 18a and the outer electrode of 19p are connected by an electrode 19pd-2 arranged on the side surface. Similarly, the base side peripheral electrode 19h of the vibrating arm 18b
The outer electrode of 19l and the outer electrode of 19l are connected by an electrode 19hl-2 arranged on the side surface. With the above electrode arrangement, the diagonal line electrodes in FIG.
19l, 19m, and 19n serve as one electrode. This will be referred to as electrode 1. Furthermore, dotted electrodes, i.e. 1
9c, 19d, 19e, 19f, 19i, 19
, 19p are the other electrodes. This will be referred to as electrode 2. In other words, an electrode placed on the peripheral edge of the tip of one vibrating arm, an electrode placed in the center of the base of the same vibrating arm, and an electrode placed in the center of the tip of the other vibrating arm. This means that the electrodes arranged on the peripheral edge of the base side of the other vibrating arm are electrically connected, and basically it is sufficient if this condition is satisfied. Cross-sectional views are shown in FIGS. 6C and 6D. Figure 6C is X- in Figure 6A.
6D is a cross-sectional view taken along the line X', and FIG. 6D is a cross-sectional view taken along the Y-Y' line in FIG. 6A. 6th
The arrows in FIGS. C and D indicate the direction of the electric field when a voltage higher than that applied to the electrode 2 is applied to the electrode 1. As can be seen from Figures 6C and 6D, if we look at the same vibrating arm, we can see that the direction of the electric field is opposite with respect to the X-axis on the tip side and the base side, with the electrical node as the boundary. Dew. Then, the vibrator 18 is excited by the second harmonic. This is because each vibrating arm of a tuning fork type vibrator can be approximated as a cantilever beam, and when the stress distribution of the second harmonic mode is determined, as shown in curve 20 in Figure 7,
This can be explained by the fact that the sign of the stress reverses at the x≒0.774×l portion. Since it is necessary to reverse the electric field near the part where the stress becomes zero, the direction of the electric field may be reversed at about 0.6 l to 0.85 l from the tip. Here, the resonant frequency f of the tuning fork type vibrator is expressed as follows. Here, S' ₂₂ and S' ₄₄ are elastic coefficients, and constant r is determined by the following equation.

Cos2r, Cosh2r=-1 ...(2) Therefore, for the fundamental wave, r ₁ = 0.9375, and for the second harmonic, r ₂ = 2.347, so if the external dimensions are constant, the second harmonic The resonant frequency of the wave is approximately six times that of the fundamental wave. In other words, by adding the electrode of the present invention to the current 32 kHz vibrator, approximately
This results in an oscillator with a frequency of 200 kilohertz. Additionally, it was experimentally confirmed that a Q value of about 200,000 can be obtained by decreasing the crystal impedance and increasing the frequency. on the other hand,
The frequency-temperature characteristics are determined by considering the temperature characteristics of each constant in equation (1), but here the second harmonic is used, that is, the constant r is changed from r ₁ → r ₂ When the width W of the vibrating arm is considered constant, it is exactly the same as multiplying the side ratio W/l by r ₂ /r ₁ , and is equivalent to multiplying W/l by r ₂ /r ₁ ≒ 2.5 times. become the same frequency. This also applies to frequency-temperature characteristics. And conventionally, the side ratio W/
It is known that the peak temperature increases by increasing l (for example: Institute of Electronics and Communication Engineers Technical Research Report VoL.76.NO22 "Analysis of 13.5° )) The same is true when using second harmonics. This fact has also been confirmed experimentally, at approximately 20°C.
It was confirmed that the peak temperature increased. Therefore, that was the original purpose. The electrode structure of the present invention achieves high frequency, high Q value, and high peak temperature without changing the external dimensions. FIG. 8 shows another embodiment of the present invention, in which side electrodes 22a, 22b, 22c, 22d, 22
By arranging elements e, 22f, 22g, and 22h over the entire side surface, an increase in driving efficiency, that is, a decrease in crystal impedance is achieved.
Note that 22a, 22c, 22e, and 22g are in the shadow and cannot be seen. The basic electrode structure is the same as the example shown in FIG. Figure 8B is X- in Figure 8A.
Cross-sectional view along the X' line. FIG. 8C is a sectional view taken along line Y--Y' in FIG. 8A. It can be seen that the direction of the electric field is reversed across the electrical node, as in the example shown in FIG. Also, the side electrodes 22a to 22
h increases the component of the electric field in the X-axis direction, increasing drive efficiency. FIG. 9 also shows another embodiment of the present invention, in which there is no peripheral electrode and the drive electrodes are comprised only of a center electrode and side electrodes. Figures 9B and C are X in Figure 9A, respectively.
It is a cross-sectional view along the -X' line and the Y-Y'line;
The peripheral electrode is removed from the example shown in the figure, and the width of the center electrode is increased to further increase efficiency. FIG. 10 also shows another embodiment of the present invention, in which the outer electrode of the peripheral electrode on the base side of the vibrating arm is removed, and side electrodes 26a, 26b, 26c,
26d with four locations. Compared to FIG. 6, since there are fewer side electrodes, the probability of connection errors is reduced and it is technically easier. FIG. 11 also shows another embodiment of the present invention, in which the outer electrode of the peripheral electrode on the base side is removed from one side shown in FIG. 11A, and the other side shown in FIG. 11B. In this case, the peripheral electrode on the tip side is removed, and side electrodes for front and back connections are provided at four locations 28a, 28b, 28c, and 28d. FIG. 12 also shows another embodiment of the present invention, in which the inner electrode of the peripheral electrode on the base side of one vibrating arm 29b is removed on one surface shown in FIG. 12A, and further, FIG. 12B In the other surface shown in , the inner electrode of the base side peripheral electrode of the other vibrating arm 29a is removed, and side electrodes for front and back connections are provided at four locations 30a, 30b, 30c, and 30d. It is. Furthermore, the electrodes arranged at the electrical nodes need not be diagonal electrodes as shown in the previous examples, but may be the same as the electrodes 31 in the form of steps as shown in FIG.
The same effect can be obtained even if electrodes 32 extending along the width direction as shown in FIG. 3B are used. In addition, Fig. 13 A and B are as follows.
Only the electrical node of one of the vibrating arms is shown. FIG. 14 shows still another embodiment of the present invention, in which the effective electrode is arranged only on the base side of the electrical node. In this case, the front and back connections are
The side electrodes 34c and 34d are provided at two locations.
Therefore, although it is technically very easy, it is necessary to compensate for the deterioration of characteristics on the circuit side. Further, in the example shown in FIG. 14, it is of course possible to apply the effective electrode to the entire side surface of the effective electrode portion, and this is shown in FIGS. 15 and 16.
As in the previous example, an increase in efficiency can be achieved by providing effective electrodes on the side surfaces as shown in FIGS. 15 and 16. 15B and 16B respectively show a sectional view taken along the line XX' of FIG. 15A and a sectional view taken along the line XX' of FIG. 16A.

By adopting the crystal resonator of the present invention as described above, the frequency is six times higher, the Q value is twice as high, and the Q value is 20 times higher than the current one, without changing the external dimensions.
It is possible to obtain a peak temperature higher than ℃. Therefore, when the frequency becomes around 200 kilohertz, the resolution of 1 hertz becomes as small as 5 x 10 ^-6 , and logical speeding up and down means can be used effectively.
Even if the frequency adjustment work of the vibrator itself is completely eliminated, an output signal having almost the desired period can be obtained, and the effect of reducing the cost of the vibrator for wristwatches is significant. Furthermore, by applying the present invention to an attempt to improve accuracy by using two vibrators, most of the conventional drawbacks can be overcome, and the effect on increasing the accuracy of electronic wristwatches is also significant.

[Brief explanation of the drawing]

FIG. 1A is an explanatory diagram showing the cutting angle of a tuning fork type crystal resonator. Figures 1B and C are a plan view and a cross-sectional view showing the electrode structure of a conventional crystal resonator, and Figure 2 is a
Oscillation circuit diagram when using CMOS. FIG. 3 is a plan view showing the remaining portion after etching. Figure 4 A is 2
FIG. 4 is an explanatory diagram showing that the frequency-temperature characteristics are improved by using two vibrators. FIG. 4B is an oscillation circuit diagram for obtaining curve 7 in FIG. 4A. FIG. 5A is an explanatory diagram showing that frequency-temperature characteristics are improved by using two vibrators. FIG. 5B is a block diagram for obtaining the curve 12 in FIG. 5A. FIG. 6 is a perspective view and a sectional view showing the electrode structure of the crystal resonator of the present invention. FIG. 7 is an explanatory diagram showing the stress distribution in the second harmonic mode of the tuning fork type vibrator. FIG. 8 is a perspective view and a sectional view showing another embodiment of the present invention. FIG. 9 is also a perspective view and a sectional view showing another embodiment of the present invention. 10th
Figures 1 to 12 are perspective views showing other embodiments of the present invention. FIG. 13 is a plan view showing another embodiment of the present invention. FIGS. 14 to 16 are perspective views and sectional views showing other embodiments of the present invention. 18, 21, 23, 25, 27, 29, 33,
35, 37...Crystal resonator of the present invention, 18a-
1, 18b-1...Tip side of vibrating arm, 18a-
2, 18b-2... Base side of vibrating arm, 19a, 1
9e, 19i, 19m...Tip side peripheral electrode, 19
c, 19g, 19k, 19... Center electrode on the tip side, 19d, 19h, 19l, 19p... Peripheral electrode on the base side, 19b, 19f, 19j, 19n...
Base side center electrode, 22a, 22b, 22c, 22
d, 12e, 22f, 22g, 22h, 24a,
24b, 24c, 24d, 24e, 24f, 24
g, 24h, 36a, 36b, 36c, 36d,
38a, 38b, 38c, 38d...Drive side electrodes.

Claims (1)

[Claims] 1. A tuning fork type crystal resonator consisting of two vibrating arms and a base connecting one end of each vibrating arm, with the length of the vibrating arms being l, and 0.6 l ~ 0.6 l from the tip of the vibrating arms.
The electrode is divided so that the direction of the effective electric field is reversed between the tip and base sides, with the part up to 0.85l being the tip side and the part from 0.6l to 0.85l to the base being the base side. crystal oscillator. 2 A front and back electrode placed at the center of the tip side of one vibrating arm, a front and back electrode placed at the base side periphery of this vibrating arm, and a front and back electrode placed at the tip side periphery of the other vibrating arm. The back electrode is electrically connected to the front and back electrodes arranged at the center of the base side of the vibrating arm, and the front and back electrodes arranged at the peripheral edge of the tip side of the one vibrating arm are connected to each other. The front and back electrodes arranged at the center of the base side, the front and back electrodes arranged at the center of the tip side of the other vibrating arm, and the front and back electrodes arranged at the peripheral edge of the base side of the other vibrating arm are electrically connected. The electrodes are divided so that they are connected to each other, and the front and back electrodes are arranged at the base side peripheral edge, and the front and back electrodes are arranged at the tip side peripheral edge.
The crystal resonator according to claim 1, wherein the front and back sides are connected by electrodes arranged on the side surfaces of the vibrating arms. 3. A front and back electrode placed at the center of the tip side of one vibrating arm, a front and back electrode placed at the base side periphery of this vibrating arm, and a front and back electrode placed at the tip side periphery of the other vibrating arm. The back electrode is electrically connected to the front and back electrodes arranged at the center of the base side of the vibrating arm, and the front and back electrodes arranged at the peripheral edge of the tip side of the one vibrating arm are connected to each other. The front and back electrodes arranged at the center of the base side, the front and back electrodes arranged at the center of the tip side of the other vibrating arm, and the front and back electrodes arranged at the peripheral edge of the base side of the other vibrating arm are electrically connected. The electrodes are divided so that they are electrically connected to each other, and the front and back electrodes arranged on the periphery of the base side and the tip side are electrically connected to the drive side electrodes arranged on both sides of the vibrating arm. A crystal resonator according to claim 1. 4 Front and back electrodes placed on the tip side of one vibrating arm, side electrodes placed on both sides of the base side of this vibrating arm, front and back electrodes placed on the base side of the other vibrating arm, and Side electrodes placed on both sides of the tip side of the vibrating arm are electrically connected, and the side electrodes placed on both sides of the tip side of the one vibrating arm and the front side electrode placed on the base side of the vibrating arm are electrically connected to each other. A patent in which the electrodes are divided so that the back electrode, the side electrode placed on both sides of the base side of the other vibrating arm, and the front and back surfaces placed on the tip side of this vibrating arm are electrically connected. A crystal resonator according to claim 1.