JPS58116810A - Frequency adjusting method of thickness-slipping crystal resonator - Google Patents

Abstract

PURPOSE:To adjust the resonance frequency of a thickness-slipping crystal resonator with couples of electrodes finely through an inexpensive device by trimming the spreading direction of the electrodes through low-voltage arc discharge work. CONSTITUTION:On a crystal oscillator blank plate 1, electrode couples 2 and 2' are provided. The spreading direction of an electrode 2 whose resonance frequency is to be adjusted is trimmed through low-voltage arc discharge work. A low voltage discharging device for trimming the spreading direction of the electrode consists of a battery E of several volts, a capacitor C, and a switch S and is equipped with connection terminals 10 and 11. Those connection terminals 10 and 11 are brought into contact with the electrode 2 and the trimming is carried out by arc discharge. Thus, the resonance frequency is adjusted finely by the inexpensive device.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency adjustment method for a whip-cut or BT-cut type thickness-stretching crystal resonator. We have developed a method for adjusting the thickness and frequency of a crystal resonator that allows for easy adjustment of the acoustic coupling coefficient between adjacent pairs of electrodes by arbitrary trimming using electrical discharge machining, and also enables stable and precise frequency adjustment. This is what we are trying to provide.

Generally, vibration energy is confined near the electrodes due to the loading effect of the electrodes mounted on the crystal resonator element plate, and the vibration displacement outside the electrodes is rapidly reduced and does not affect the surrounding areas (this is a so-called energy trapping type). A typical crystal resonator is shown in FIG.

In Fig. 1, 1 is an AT-cut crystal element with a thickness of tl, and this resonator plate (1) can have any shape such as a circle, quadrilateral, or triangle, but here it is shown as a circle (its diameter is φ!). . 2 is a good conductive metal with a thickness tx, such as gold, silver, steel/aluminum, nickel, etc. Here, silver is used as the upper and lower electrodes, which are attached to the upper and lower surfaces of the vibration pre-electrode 1 [1, respectively. . 5 and 4 are lead portions of the upper and lower electrodes 20, respectively, and the diameters of the upper and lower electrodes are shown as φ.

An example of an energy trap type crystal resonator formed in this embodiment will be explained.

The field stiffness C-e' of a whip-cut crystal resonator is C-
-m 2 9.2 1 x 1 0” dyn@
Since Pt=2.65g/-, when n=x1, ttf@=1.66 (mm, MH,) river (2).To simplify the explanation, for example, vibration precharge 1 [
Thickness (ts) of electrode 1 is tl=a164mm, diameter (φ,) is -φr-&Omm: Thickness (ts) of J electrode 2o is ts
=(LOOO2, from Toi to crystal volume 1 [1 can be said to be a non-ferrous plane, and it can be explained by ignoring the distance of the electric current and the shape and finish of the area around the crystal resonator 10. Under these conditions The resonant frequency f of the crystal resonator at is determined by the energy-confined vibration theory as a function of the aforementioned f·, 4 e b and Δ related to the loading effect of the electrodes.

The density is P,=1α50g/,i. This equation (3) shows the factors that determine the resonant frequency of the resonator (1 bar 4
) 俤), (n*c@・′ν1
+ tl eplet2. It becomes φko]. Since this factor circle n*Can' e Pt is predetermined as described above, the remaining (ts·ts#p2.φ3) is the design theory K11l factor. The relationship between this group of independent factors and the resonance frequency f of the crystal resonator, which is the lowest fundamental frequency of the energy trapping mode, can be established using parameters as mediating variables.

For example, when n=1, the resonance lI wave number f is f=f・(1−R
s in”#) ”’ (6) 1” tL L
. ko (6)
7:) shows the root. In this equation (7), k is normally the same value as the anisotropic coefficient, but here the electrode is circular,
If the above-mentioned Δ is made to be approximately Q, 71 including a correction that approximates R, it agrees with the experimental value.

The resonant frequency f of the crystal resonator is determined by the above preparation as shown in Figure 2.The resonant frequency f of the crystal resonator can be expressed as (21(5) (8) in equation (6) as a specific equation corresponding to equation (3) above. ).For example, if this resonance frequency f is calculated using the dimensions of the blank plate 1 and the electrode 2, then f=10.OMth.

The cost of adjusting the resonant frequency in manufacturing such an energy-trapped crystal resonator will be explained first, and then the conventional frequency adjusting method and its drawbacks will be explained below.

In general, in a typical manufacturing process of a crystal resonator, the thickness (tl) of the crystal base plate 1 is designed taking into account the frequency return due to the load effect of electrode deposition in the second term in parentheses of equation (9). On the other hand, as shown in the thickness of the crystal plate of 1.005 tr, the accuracy of the crystal plate by mechanical polishing is ±Q, 1596 (0,25
μ). Next (10005ts.

In the process of chemical polishing, tl is
Finished within the deviation of α08μ). After that, the thickness (
tm) electrodes are attached. In this case, even if the thickness of the electrode (tl) is as desired, it already has a deviation of 50 ppm, but this deviation of (tm) and the surface roughness of the crystal plate, which was not included in equation (9), The slight influence of parallelism, support mechanism, etc. cannot be overlooked here, so these must be added. Therefore, in total, the frequency deviation is ±1
00 pI)m must be considered as being. Such a frequency deviation of 100 PPn1 must be adjusted to a desired frequency deviation (for example, adjusted to ±2 ppm), but methods for doing so include ■electrochemical polishing, ■electrochemical plating, and [F] vapor deposition. 375 law is generally expressed in rows. What these conventional methods have in common is that the electrode 2
The thickness (t) must be adjusted.

For example, in the 0 method, it is effective only when decreasing the thickness (tl), and in the ■ method, it is effective only when increasing the thickness (1 snow), but in these ■■ methods, the electrolyte solution is Component concentration and temperature control 1. Since it is not easy to control the amount of electrical charge (especially in terms of time), a high degree of skill is required to adjust it to within ±20p. Moreover, it takes time to remove the electrolytic solution, and there is a great possibility that the minute amount of residual electrolytic solution may cause the electrode to deteriorate over time, that is, the resonance frequency f may change. In addition to these drawbacks, since the frequency adjustment operation is performed in the electrolyte, it is not possible to operate the crystal resonator as an oscillator or resonator in an electric circuit and directly observe the degree of adjustment. A particular problem is that, for example, when adjusting the resonant frequency of a pair of four pairs of thickness-stretching resonators as shown in Figure 3, the other pairs of electrodes that do not require adjustment must also be immersed in the electrolyte. Unfortunately, the thickness of the electrode in these non-energized parts also changes, making it difficult to independently adjust the counter electrode as desired.

On the other hand, in the other vapor deposition method shown in (1), the electrode thickness (tl)
This vapor deposition method is effective in increasing the frequency, and does not have the disadvantages mentioned above. However, although it is natural that frequency adjustment must be performed in a vacuum, it is not easy to punch the coating mask of the adjustment electrode part. Furthermore, it is not easy to control the minute thickness of the coating, that is, the small amount of metal vapor deposition, to a desired setting value.

Solving these problems requires expensive equipment, and fine adjustment of the frequency (a ppm) is limited by the frequency measurement time and the speed limit of the shutter that stops the deposition of silver forming the electrodes. Since the temperature is lowered to evaporate and a minute amount of evaporated metal particle flow having only weak energy is used, the adhesion state thereof is poor (there are problems such as aging of the resonance frequency f, etc.).

With the above points in mind, we will specifically explain how the resonant frequency was conventionally adjusted in the acoustically coupled multi-pair electrode resonator according to the present invention.

Taking as an example a thickness-stretching crystal resonator with four pairs of electrodes shown in figure wJ3, electrodes 2, 2' and 2I are placed on the vibrating cotyledon plate.

The same applies to the case where the electrodes 21I are respectively mounted and have two or three pairs of rounded rectangular electrode pairs on a mezzanine crystal plate (not shown). For example, by connecting the crystal resonator with four pairs of force electrodes as shown in Fig. 4, x, T', l
, l/ constitutes a 4-terminal circuit to form a monolithic crystal filter. In order to satisfy this filter specification characteristic, in Fig. 3, the alignment force of the electrode with respect to the crystal axis of the crystal plate (in this case, the axis T tilted approximately s': i s' from the optical axis 2), The electrode area (L, wi), electrode spacing (gij), electrode thickness (tm), etc. are determined with respect to the thickness of the crystal plate (tl), but the issue here is the phase to be focused on. This is a case where the acoustic coupling coefficient between adjacent pairs of electrodes is adjusted to match the electrical coupling coefficient designed by the corresponding electrical equivalent circuit. - For example, if the adjacent electrodes 2 and 21 are connected as shown in Figure 5(a), the series resonance frequency (fl) will be the same, and if they are connected as shown in Figure 5(bl), the resonance frequency J!!(fm) will be can be measured respectively, and the boundary conditions are inserted into the elasticity equation 75 corresponding to the vibration mode of these resonant frequencies, and the solution is obtained.For example, after finding the solution to the transcendental equation as mentioned above, rewriting it dimensionally and structurally gives F. By determining the relationship, it can be approximated as follows.That is, in this equation (b), the constant kl is the ratio of the speed of the propagating wave, that is, the term related to the stiffness of the crystal.
'The electrodes are lined up in the force direction.'This is a correction constant when the right side of the force equation is approximated to an algebraic equation, and W + in the commonly used range.
g Hil , km for △ = a78 and D' k
s = 2.88 degrees L larel.

When adjusting the coupling coefficient F obtained in this way,
As is clear from Equation 09, r actually measured using the above method usually deviates from the designed F due to manufacturing errors of w, g+tt+t*, so! .

By adjusting g + h, it is possible to make the desired FK correction. Here, the crystal base plate thickness (tl) is ±0 as mentioned above.
．． It was excluded because it was finished with a high accuracy of 0.5% and could not be corrected after the electrode was attached. Now, by increasing or decreasing the electrode thickness tl, the coupling coefficient F can obviously be adjusted in relation to the expression α9, but the natural frequency of each electrode pair 2.2' also changes greatly depending on the electrode thickness (t3). Therefore, it is preferable and powerful. Therefore, the first consideration is to adjust the width of the electrode 2.2'. For this, the outside and inside of the width of the electrode 2.2' can be considered [Fig. 5 (g side of at)]. For example, when adjusting the inside (g side) dimension, refer to item 1 on the right side of the al formula. As can be seen, adjusting the inner dimension (g side) has no effect because the dimension of the gap between the adjacent electrode pairs 2, 2' changes accordingly.

Therefore, in conventional dimensions, the total dimension 2t of the respective thicknesses (tm) of the upper and lower electrodes 2 and 2' is kept constant, and the thickness (tm') of each of the upper and lower electrodes is increased or decreased. (2 tl = t*'+tm'). As an example of this method, as shown in FIG. 6(a), the space between the adjacent lower electrode pairs @ (A'-B') is made smaller than the space between the upper electrode pair, or wI6 figure(
Either the lower electrodes are integrated as a common electrode as shown in b), or, unlike these methods, a new electrode 2 is provided in the gap between the adjacent pairs of lower electrodes as shown in Figure 6 (cl). , the acoustic coupling coefficient (r) is adjusted by adjusting the thickness of this electrode 2.

What these methods have in common is that the electrodes 2, 2
'The natural frequency of each counter electrode also varies greatly depending on the thickness (tl) of the electrode. al As shown in (b), the thickness of one upper electrode CM'
), the thickness of the lower electrode (11) is required to be corrected, resulting in two operations being required.Note that this method is different from the conventional method. A method has been proposed to adjust the width of 2, 2' or the space H (g) dimension between adjacent electrode pairs. This means that it becomes expensive.

The present invention was invented in view of this point, and in the case of a multi-pair electrode structure, dimensions such as the area (electrode width x electrode length) of the electrodes facing between pairs of electrodes that are compatible with each other are The acoustic coupling coefficient between opposing pairs of electrodes can be adjusted by arbitrarily trimming using low-voltage arc discharge machining, and the device itself provides a simple and inexpensive frequency adjustment method for a thickness-stretching crystal resonator. It is in.

Next, an embodiment of the device for trimming the spreading direction of the electrode according to the present invention is shown in FIG. 7 and FIG.
The operation of electrical discharge machining will be explained in detail with reference to FIG.

Fig. 7 shows an example of a storage type low voltage discharge device.
A switch S is connected to the capacitor C, which is closed when the capacitor C is charged with electric charge consumed in electrical discharge machining prior to discharge, and this switch S is opened when charging is completed. In addition, in the embodiment where the capacitor C has an appropriate capacity, 20 μF is used, and a resistor r is inserted at one end of the capacitor C to soften the discharge, as shown in the figure.
This resistance r is generally a composite resistance of the internal resistance of the capacitor C and the resistance of the connection line, and a metal with a sharp tip, for example a cotton needle 10, etc., is connected via this resistance r. On the other hand, an ordinary connection terminal 11 is connected to the other end of the capacitor C, and this terminal 11 may have the shape of the terminal 10, for example. FIG. 8 shows another embodiment, which is an example of a non-storage type device. , in this Figure 8, the commercial power supply 1 is connected via the transformer T.
The circuit configuration is characterized by insulating 00 (V) and lowering the voltage to an appropriate discharge voltage M, where r and 10°11 are respectively
It is the same as that explained in the figure.

Although not shown, in order to finely adjust the discharge voltage, a tap may be provided on the secondary side of the transformer T, or a commonly used slider may be inserted on the primary side.

When adjusting the resonant frequency of a pair of electrode structures as shown in FIG. 1 using the low voltage discharge device constructed in this way, for example, as shown in FIG. When the processing terminal 11 is brought into contact with the lead part 6 of the electrode 2 and one terminal 10 such as a cotton needle is brought into contact with the peripheral edge of the electrode 2, the electrode 2
If silver is silver, the silver electrode 2 is heated by the contact resistance, ionizes, and evaporates. As a result, a minute gap is formed, an arc discharge phenomenon is observed, evaporation is accelerated, and the electrode 2
is trimmed (row). After that, the terminal 10 is gradually moved around the edge of the electrode 20, and although this operation is not shown, the frequency is continuously detected via the detector according to the amount of trimming, and the desired frequency is detected. Trimming by arc discharge machining is continued until the electrode 2 is a chain.If the electrode 2 is a chain, the minimum arc voltage in the atmosphere is 12.3 (V'l), but if a voltage around this value is applied to the crystal blank, the experiment Generally speaking, the element 1 will be destroyed, so it is better to lower the voltage to around 3-5 concavities, for example.

Examples of the effects of electrode trimming are shown in Figure 10 and Figure 1.
This will be explained using Figure 1.

The amount of frequency change (d f/f ) in the case of trimming using the apparatus shown in Figure 7 with the above optimal applied voltage is
What is shown in Fig. 10 is this summary Fig. 10 [The horizontal axis represents the number of trimmings and the vertical axis represents the cumulative frequency change amount (df/f;
ppn+) respectively. ] As can be understood, the amount of frequency change increases relatively depending on the number of trimmings, so in the present invention, it is extremely difficult to finely investigate the frequency, for example, adjust it to ±2 ppm, as in the conventional method. However, in the above description, a method of adjusting the frequency by trimming, for example, by moving the peripheral part of the electrode 20, has been shown, but in the present invention, this method For example, in the crystal resonator shown in FIG. 1, the frequency can be adjusted by trimming any part of the inner surface of the electrode 2 to any size. In order to clarify the effect, the same size of approximately 0, [12
-), FIG. 11 shows the trimming position on the horizontal axis and the amount of frequency change (d f/f; p failure) on the vertical axis. ] As shown, the end CB of 1 electrode 2.

Btt ), the amount of frequency change is small, and as it approaches the center point (B') of the secondary electrode 2, the amount of frequency change gradually increases, and the amount of frequency change becomes maximum at the center point (B'). The magnitude of the frequency change (df/f'w) that changes depending on the position is approximately the same as the vibration displacement during resonance, and the magnitude changes depending on the angle formed with the crystal axis of the B-B' force direction crystal vane plate 1. The shape is condensed and its absolute value is proportional to the size of trimming. Therefore, if the position of trimming is selected according to the desired amount of adjustment, the objective can be easily achieved with trimming of the same size.

When using this triangulation method to calculate the acoustic coupling coefficient between adjacent pairs of electrodes in a crystal resonator by varying the thickness of multiple pairs of electrodes,
For example, if the lower surface electrode is commonly exposed in the two-pair electrode structure shown in FIG. is trimmed arbitrarily by low-voltage arc discharging process, and the mass of this central m opening is gradually removed to form the void shown in Fig. 6 (Fig. 6).
It expands to B'). During this trimming process, changes in the resonant frequency (fl) in the symmetrical mode connected as shown in Figure 5 (at) and changes in the resonant frequency (fm) in the oblique symmetrical mode connected as shown in Figure 5(b) are observed. ), and the change in the acoustic coupling coefficient (/') based on the change in the resonant frequency II (ft) (f) is shown in Figure 12 [The horizontal axis shows the trimming ratio A/B// AB is represented by the acoustic coupling coefficient (r) and the resonance frequency of electrode 2゜2' on the vertical axis #IQ, 7MI
The resonance frequency changes in the symmetric mode and the oblique symmetric mode with respect to k are shown, respectively. ] According to the present invention, the acoustic coupling coefficient Cr) between adjacent pairs of electrodes can be easily adjusted by low-voltage arc discharge machining. In addition, according to the present invention, the electrode 2 is
It is also possible to leave an empty space I! between adjacent pairs of electrodes. 1
For example, A A' and BB in Fig. 6(b) are trimmed.
'A A' and B B' without making them the same size
By making the electrodes 2 and 2' different in size, it is possible to eliminate differences in the resonance frequencies of the electrode pairs 2 and 2'.

As described above, in the present invention, the spreading υ direction of the electrode is arbitrarily trimmed by low-voltage arc discharge machining to obtain a desired resonance frequency or a desired acoustic coupling coefficient between adjacent pairs of electrodes. Therefore, it has various advantages as shown below.

■ Fine frequency adjustments such as ±lppm can be made without requiring any skill in trimming operations.

■ Trimming adjustment can be made while monitoring the desired frequency by connecting to a driving device such as a CI meter. ■ Trimming can be done not only in the atmosphere but also in any atmosphere.

■ It has a multi-pair electrode structure, which allows adjustment without affecting electrodes other than the one to be adjusted.

■ Stable and fine frequency adjustment or acoustic coupling coefficient adjustment is possible with a simple and inexpensive device.

■ Since the metal in the trimmed area is evaporated and atomized by arc discharge, cleaning operations after adjustment are usually unnecessary.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are a plan view and a longitudinal side view of a typical AT-cut thick sliding crystal resonator, respectively, and Figure 2 shows the 5inj # and counter electrode thickness in one process of obtaining the resonant frequency. A perspective view and a vertical side view showing a quartz crystal resonator, Fig. 6 ←→ is an optical axis (2') tilted as an AT plate and a CBT plate)
Figure 4 is a connection diagram showing a monolithic filter, and Figure 5 (a) and false) are two-pair electrode structures and symmetrical modes, respectively. and connection diagram for obtaining the resonant frequency in obliquely symmetrical mode, No. 6
Figures (1) (b) and (cl) are specific examples of adjusting the acoustic coupling coefficient in a multi-pair electrode structure, respectively. Figure 7 is a connection diagram showing a specific embodiment of the present invention. Figure 8. 9 is a connection diagram showing another specific embodiment of the present invention. FIG. 9 is a specific example diagram showing trimming work in low voltage arc discharge machining according to the present invention. FIG. 10 is a diagram showing the number of times of trimming in the present invention. Characteristic diagram showing the relationship between and the cumulative frequency change amount, 1st
Fig. 1 is a characteristic diagram showing the relationship between the trimming position and the amount of frequency change in the present invention, and Fig. 12 is a characteristic diagram showing the relationship between the trimming ratio and the acoustic coupling coefficient, and the resonant frequency of the symmetric mode and the oblique symmetric mode in the present invention. A temporal diagram showing the relationship. (1) is a crystal resonator element plate, (2) (27'(2)'
(2) are electrodes, (3) and (4) are their leads, (2) and αυ are processing terminals, and (C1(
81@) are the voltage power supply, capacitor switch, and resistor, respectively. Figure 2 Fs (Tori R) ε 31st! I Figure 4 Figure 5 (a (1)) 10th country and Rimi/ri U3 wife (1st f t!!) --□ Trimming φi T1.屓

Claims (2)

[Claims] (1) Many pairs of electrodes are deposited directly on the resonator base plate without leaving the JLL of a thick ink resonator such as a whip cut or BT cut in a free state, so that the electrodes become part of the resonator. In order to adjust the frequency of the resonator that vibrates as a A method for adjusting the frequency of a thickness-stretching crystal resonator, characterized in that the acoustic coupling coefficient between a pair of electrodes is adjusted by arbitrarily trimming during processing, thereby adjusting the resonant frequency of the resonator. (2) In Section 11 of Claim 41, an isolated internal widening portion on a pair of electrode surfaces focused on in an electrode group can be arbitrarily processed by low-voltage arc machining to any size and location. A method for adjusting the frequency of a thick crystal resonator, characterized in that the acoustic coupling coefficient between the pair of electrodes is adjusted by trimming the resonator to adjust the resonant frequency of the l&satin.