JPS5839105A - Compensating method for frequency-temperature characteristic of surface acoustic wave resonator - Google Patents

Abstract

PURPOSE:To make frequency-temperature characteristics coincident with one another among plural resonance frequencies, by setting the ratio of the width of electrode fingers to the width of no-electrode parts between electrodes to a desired value. CONSTITUTION:Three bus bar electrodes 2, 3, and 4 are provided in the X-axial direction on the main surface of an ST cut quartz substrate 1, and the center bus bar electrode 3 is used as a common electrode for both resonators to excite two kinds of resonance frequency. When resonance frequencies, surface wave wavelengths, widths of electrode fingers, and widths of no-electrode parts of respective resonators and the thickness of electrode films are denoted as f1 and f2, lambda1 and lambda2, l1 and l2, s1 and s2, and (h) respectively, both resonators show the same peak temperature on condition that l2/l1=(lambda2/lambda1)<2>=(f1/f2)<2> is true. Consequently, the frequency f1 of the resonator as a reference is determined, and the quartz cut angle and the electrode finger width l1 are so determined that the peak temperature of frequency-temperature characteristics becomes a prescribed value, and thus, the electrode finger width l2 of the resonator having the frequency f2 is obtained automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of compensating for frequency-temperature characteristics of a surface acoustic wave resonator.

As is well known, when a surface acoustic wave resonator is constructed by providing multiple pairs of interdigital transformers and electrodes on a crystal substrate, its frequency-temperature characteristics are basically determined by the cut angle of the crystal substrate. At the same time, it changes depending on the resonant frequency of the resonator (this is determined by the pitch of the interdigital transistor electrodes) and the electrode film thickness.

Therefore, when designing a resonator using a quartz substrate, it is necessary to determine the cut angle of the quartz substrate in consideration of the interdigital transistor, the pitch of the -circuit electrodes, and the electrode film thickness.

In particular, when multiple resonators of different types are provided on the same crystal substrate with electrodes of the same film thickness, each frequency exhibits a different frequency-temperature characteristic, and it is virtually impossible to compensate for this. Met.

This invention was made in order to solve the above-mentioned drawbacks of the conventional resonator, a surface acoustic wave resonator equipped with multiple pairs of interdigital transducer electrodes at 41. The ratio of the electrode finger width of the electrodes to the width of the non-electrode portion between the electrodes is selected so that the mass addition effect of the interdigital transformer and -sa electrodes provided in the electrodes provides the best frequency-temperature characteristics regardless of the resonance frequency. An object of the present invention is to provide a method for compensating the frequency-temperature characteristics of a surface acoustic wave resonator.

Hereinafter, the present invention will be described in detail based on Examples and experimental results.

If we take as an example a surface acoustic wave resonator using an ST-cut crystal substrate which has the best frequency-temperature characteristics, this resonator will have a configuration as shown in FIG.

In other words, when considering a resonator that excites two types of resonant frequencies on a single crystal substrate and selects one of them as necessary, the X-axis on the main surface of the ST-cut crystal substrate 1 Three passbar electrodes 2.3 and 4 are provided in the direction, and the central busbar electrode 3Yt serves as a common electrode for both resonators.

A large number of ink digital electrode fingers 5,5. -..., 6.6.・・・・−
as well as? , 7,---18 ,8,------
are extended so as to intersect with each other to form a so-called regular type interdigital transducer electrode tube.

As is well known, the electrode may be manufactured by etching the metal film K1 deposited on the substrate 1 into a predetermined pattern by photo-etching or the like.

Needless to say, if the wavelength of the surface acoustic wave excited by the electrical energy applied to the interdigital transformer is λ1, it is necessary to design it so that the wavelength is 11+s-λ1/2. , it is common to set 11=81 from the viewpoint of ease of manufacture.

Next, the frequency-temperature characteristics of the elastic w-wave resonator as described above will be described. The temperature characteristics of the resonator are primarily determined by the cut angle of the crystal, and a 38° rotated Y-cut plate, commonly called KFiST cut, is used. Its temperature characteristic is a quadratic curve with a zero temperature coefficient near normal temperature.

Furthermore, the second factor that determines the temperature characteristics is the thickness of the electrode and the width of the electrode.If the electrode tube is thicker and the electrode @ is wider, the peak temperature will be lower due to the added mass effect of the electrode. Shift to the side.

This becomes more noticeable as the frequency becomes higher. Therefore, when multiple resonators are provided on a single substrate, the temperature characteristics of the low frequency resonator and the high frequency resonator will be different.

That is, the peak temperature of the low frequency resonator shifts to the high temperature side, and the peak temperature of the high frequency resonator shifts to the low temperature side, so that the temperature characteristics of the image collectors do not match. This shift increases as the frequency difference increases. To give an example, two frequencies 6
The 1.25 MHz and 67.25 MHz resonators are the first
As shown in the figure (assuming that it is fabricated on an 8'l' cut crystal substrate), the frequency-temperature characteristic of each resonator shows a quadratic curve. If the cut angle of the substrate crystal is selected to obtain the best frequency-temperature characteristic according to the peak temperature of Therefore, when considering ways to improve this problem, since it is well known that the frequency-temperature characteristics of this resonator depends on the mass addition effect of the electrode attached to the surface, the electrode of the image collector It can be seen that different film thicknesses can be used. However, such a method makes electrode deposition difficult and manufacturing complicated.

Therefore, in the present invention, the ratio IP of the electrode finger width of the -sa electrode to the non-electrode part width of the interdigital transformer is changed so that the mass addition effect is the same for the electrodes corresponding to both frequencies. The objective is to match the temperature characteristics.

That is, the resonant frequency of two resonators provided on the same substrate,
The surface wave height, electrode finger width and non-electrode part width are f1, fzwλl and λ!, respectively. ,! 1 and l! and Ksl and 32
Assuming that both electrode film thicknesses are equal and h is the same, the condition for both valve vibrators to have the same peak temperature is that the electrode material adheres uniformly to the entire surface of the substrate. Since the values normalized by the length are considered to be equal, if the surface wave propagation velocity is υ, then fl・λt=fz・λ3=u ・・・・・・・・・・・・・・・
・(3) Obtain t from the above (1), (21 and equation (3).

Therefore, by determining the frequency f1 of the resonator as a reference, and determining the peak temperature *1 of the frequency-temperature characteristic - for example, the angle and electrode finger width jxt of the crystal so that the room temperature is 25°C, the resonator of frequency f2 is determined. Electrode finger width! Mushrooms can be found automatically.

Furthermore, it is obvious that the temperature characteristic compensation method according to the present invention as described above can be applied to a resonator that oscillates not only two frequencies but also several frequencies; in this case, the reference resonance The electrode finger width of the fil@th resonator with respect to the electrode finger width 11 of the resonator! .

By setting , it is possible to match all the frequency-temperature characteristics.

Finally, the method according to the present invention was applied to 61.25 and 67.25M.
Experimental results when applied to a Hz dual-frequency resonator will be explained.

First, if the ratio of the electrode finger width to the non-electrode width of the resonator corresponding to the image frequency is 1:1, then the peak temperature of the resonator of 67°25MHz is 25°C.
Accordingly, the peak temperature of the 61.25 MH resonator shifts to the higher temperature side by about 5°C. (The surface acoustic wave propagation speed on the main surface of the quartz crystal substrate is 3130 m/
Since s, λ1 = 46.543 μm, therefore j1 = 8
s°λ, /4-11・635μm, therefore 72=14.0
It becomes 33 μm.

l　s=11.518　Jim.

Therefore 12: S m-14,033: 11.51
B"q5: Designed to be dangerous at 4.

The frequency-temperature characteristic of a resonator designed in this way is the third
As shown in the figure, both 67.25 MHz and 61.25 MHz have peak temperatures of 25°C.

Since the present invention is constructed as described above, in a surface acoustic wave resonator capable of selectively resonating a large number of different frequencies on a single piezoelectric substrate, all resonators have substantially the same %frequency-temperature characteristics. Not only can the M characteristics of the resonator be made uniform, it is extremely effective when applied to equipment that requires the use of a wide variety of frequencies, such as VTRs.

Note that the present invention is not necessarily applied only to surface acoustic wave resonators, but is similarly applicable to resonators that utilize waves that propagate directly beneath a piezoelectric substrate, such as 88BW.

[Brief explanation of the drawing]

Figure 1 shows the configuration of a surface acoustic wave resonator capable of two-frequency resonance. Figure 2 In the resonator shown in Figure 1, the ratio of the electrode finger width l to the non-electrode width 3 FIG. 3 is a diagram showing the difference in frequency-temperature characteristics in the case of l:l, and FIG. 3 is a diagram showing experimental results when the present invention is applied to the resonator of FIG. 1. 1 is a piezoelectric substrate, 5, 6, 7 and 8 are interdigital
Transducer electrode, 11m1 means electrode ring%S1*
Im is the width of the non-electrode portion, λ1. λ indicates the wave length of the elastic surface excited by the image collector, respectively. Patent applicant: Toyo Tsushinki Co., Ltd.

Claims (1)

[Claims] In a surface acoustic wave resonator in which multiple pairs of interdigital transformer electrodes are provided on the same crystal substrate and can resonate different frequencies, one resonant frequency group or one of the other The resonant frequency of is fn, and the electrode finger width of the interdigital transducer electrode corresponding to the frequency is 11. By setting the electrode finger width of the electrode so as to satisfy the following relationship, when 1B, the influence III of the mass load effect due to the electrode film thickness of the plurality of resonators is equalized, and each frequency-temperature [ Il! f
A method for compensating frequency-temperature characteristics of a surface acoustic wave resonator, which is characterized by matching the characteristics.