JPH0728196B2 - Surface acoustic wave resonator device - Google Patents

Description

The present invention relates to a surface acoustic wave resonator device, and more particularly to a surface acoustic wave resonator device that resonates at a plurality of frequencies.

(Prior Art) Generally, a surface acoustic wave resonator device has a pair of comb-teeth electrodes 2a, 2a on a piezoelectric substrate 1, as shown in FIGS. 4 and 5.
And an excitation electrode 2 intersecting with each other, and two sets of grating reflectors 3 and 3 arranged so as to sandwich the excitation electrode 2.

The surface acoustic wave excited by the excitation electrode 2 propagates on the piezoelectric substrate 1 and is reflected by the reflector 3 to generate a standing wave having a wavelength twice the pitch P of the grating reflector 3. That is, it is configured as a vibrator having a high unloaded Q.

FIG. 6 is a diagram showing an equivalent circuit of such a surface acoustic wave resonator device, in which a parallel capacitance C2 of the excitation electrode 2 is connected to a resonance circuit composed of L1, C1, and R1. is there.

Also, such a surface acoustic wave resonator device can be represented as a series impedance circuit. FIG. 7 is a diagram showing such an impedance circuit, which is a combination of the resistance Re and the reactance Xe. Then, the reactance Xe becomes inductive between the resonance frequency and the anti-resonance frequency, that is, it becomes an inductive element.

FIG. 8 is a diagram showing an example in which a surface acoustic wave resonator device utilizing such characteristics is inserted in the Colpitts oscillator circuit 4. An impedance circuit between terminals A and B in this figure is shown in FIG. That is, the impedance on the Colpitts oscillator circuit 4 side is the capacitive reactance.
It can be expressed as a series connection of Xc and negative resistance −Rc, and it becomes an LC resonance circuit at the frequency fosc that satisfies Xe (fosc) = −Xc Re (fosc) ≦ Rc and oscillates at this frequency. .

FIG. 10 is a diagram showing the amplitude characteristic of the surface acoustic wave resonator device shown in FIG. In the figure, fr is the resonance frequency, fa is the anti-resonance frequency, Ar is the resonance loss, and Aa is the anti-resonance loss. In this case, the resonance loss Ar greatly affects the oscillation level when the surface acoustic wave resonator device is inserted in the oscillation circuit. That is, the smaller the resonance loss Ar, the higher the oscillation level.

By the way, in recent years, such a surface acoustic wave resonator device has come to be used as an oscillator of an oscillator of a video tape recorder, a personal computer, a compact disc player or the like. For example, the above video tape recorder has a built-in RF converter circuit that outputs a carrier wave to convert a reproduction signal into a frequency of a radio wave for broadcasting. Since a highly stable oscillation circuit can be realized by using a surface acoustic wave resonator device as an oscillator of the oscillator of this RF converter circuit, its use is actively used.

By the way, in general, a video tape recorder is required to output two kinds of frequencies, that is, radio waves for broadcasting of two channels (for example, 91.25 MHz and 97.25 MHz in Japan). Also needs to output carriers of two different frequencies. In this case, it is necessary to excite two kinds of frequencies even in the surface acoustic wave resonator device. As an example thereof, there is one in which two sets of resonators are formed on the same piezoelectric substrate in consideration of manufacturing cost.

By the way, such a surface acoustic wave resonator device has a resonance loss Ar1 of a resonator electrode of a low frequency fr1 and a resonance loss Ar2 of a resonator electrode of a high frequency fr2 as shown in FIG.
When there is a difference between and, the oscillation level becomes non-uniform, and the oscillation circuit constant must be set at each oscillation frequency. For example, two oscillation circuits are required.
Therefore, in the above case, it is necessary to set the resonance loss Ar1 and the resonance loss Ar2 to values close to each other.

(Problems to be Solved by the Invention) In the production of the above-described surface acoustic wave resonator, when both the excitation electrode and the grating reflector are formed of a metal thin film, if workability is taken into consideration, resonance at a low frequency is generated. It can be simplified by making the electrode film thickness of the container the same. Here, the wavelength of the low frequency resonator is λ ₁ , and the wavelength of the high frequency resonator is λ ₁ .
₂ , and the electrode film thickness is h, h / λ ₁ <h / λ ₂ . Since the surface wave reflectance ε at the reflector has a relation of εA · (h / λ) (A is a constant), ε ₁ <ε ₂ (ε ₁ ; Reflectance at a low frequency reflector, ε ₂ ;. The reflectivity of a high frequency reflector) and the resonance loss Ar ₁ and the resonance loss Ar ₂ generally tend to be Ar ₁ > Ar ₂ and a difference occurs between the resonance losses of both resonators.
As a means for reducing the difference between the resonance loss Ar ₁ and the resonance loss Ar ₂ as described above, for example, as shown in Japanese Patent Application No. 57-109354, the film thickness of the low frequency resonator electrode is set to the high frequency resonator electrode. There are a thicker one, a different material between these resonator electrodes, and the like. However, in such a case, the electrode pattern forming process becomes complicated,
Further, there is a problem in workability because a difference in etching rate occurs during photoetching. Also, it is possible to reduce the number of reflective electrodes of the high frequency resonator electrode to increase the resonance loss of this resonator electrode.
There is a problem in that due to variations in film thickness and the like, manufacturing variations occur in the resonance loss between the surface acoustic wave resonator devices and the yield decreases.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to make the resonance loss the same between resonators having different resonance frequencies and to reduce the manufacturing cost. It is intended to provide a device.

[Structure of the Invention] (Means for Solving the Problems) That is, in the surface acoustic wave resonator device of the present invention, a substrate for propagating surface acoustic waves intersects a pair of comb-teeth electrodes formed on the substrate. And a plurality of surface acoustic wave resonators having different resonance frequencies, the surface acoustic wave resonator including an exciting electrode and a grating reflector formed on the substrate so as to sandwich the exciting electrode. In the surface acoustic wave resonator device arranged individually, the grating reflector width WL of the surface acoustic wave resonator that resonates at a low frequency fr1.
Value obtained by dividing 1 by the above-mentioned low frequency surface acoustic wavelength λ1 WL1 /
The relationship between λ1 and the value WL2 / λ2 obtained by dividing the grating reflector width WL2 of the surface acoustic wave resonator that resonates at a high frequency fr2 by the surface acoustic wave wavelength λ2 at the high frequency is WL1 / λ2.
1> WL2 / λ2 and WL2 / λ2 <10.

(Operation) In the surface acoustic wave resonator device of the present invention, a low frequency fr
The value WL1 / λ1 obtained by dividing the grating reflector width WL1 of the surface acoustic wave resonator that resonates 1 by the surface acoustic wave wavelength λ1 of the low frequency, and the grating reflection of the surface acoustic wave resonator that resonates the high frequency fr2. The relationship between the width WL2 divided by the high frequency surface acoustic wave wavelength λ2 and WL2 / λ2 is set to WL1 / λ1> WL2 / λ2 and WL2 / λ2 <10, so resonance occurs between resonators with different resonance frequencies. The loss can be set to the same value, and the manufacturing cost can be reduced.

(Example) Hereinafter, the detail of the Example of this invention is described based on drawing.

FIG. 1 is a diagram showing a surface acoustic wave resonator device according to an embodiment of the present invention, and FIG. 2 is a partially enlarged view thereof.

In the figure, reference numeral 11 is a piezoelectric substrate made of LiTaO3, LiNbO3, crystal, or the like, and two sets of resonators 12 and 13 having different resonance frequencies are formed on the piezoelectric substrate 11. One resonator 12 resonates at a low frequency fr1,
Comb-shaped electrode with a large number of electrode fingers 15 protruding from the bus bar 14
It is composed of an excitation electrode 17 formed by intersecting two sets of 16 and two sets of reflectors 18 and 18 arranged so as to sandwich the excitation electrode 17. The other resonator 13 resonates at a high frequency fr2, and sandwiches this excitation electrode 22 with an excitation electrode 22 formed by intersecting two sets of comb-teeth electrodes 21 each having a large number of electrode fingers 20 protruding from the bus bar 19. Pairs of reflectors arranged in
It is composed of 23 and 23. The bus bar 14 on the other resonator 13 side of the excitation electrode 17 of the one resonator 12 and the bus bar 19 on the one resonator 12 side of the excitation electrode 22 of the other resonator 13 are the same, that is, shared. It is supposed to be used.

The reflector 18 of the resonator 12 that resonates at the low frequency fr1 described above.
The value obtained by dividing the reflector width WL1 of the above by the wavelength λ1 of this frequency, that is, the normalized value is WL1 / λ1. Also high frequency
A value obtained by dividing the reflector width WL2 of the reflector 23 of the resonator 13 that resonates fr2 by the wavelength λ2 of this frequency fr2, that is, a normalized value is WL2 / λ2. Then, these normalized values WL1 / λ
1 and WL2 / λ2 are set to have a relationship of WL1 / λ1> WL2 / λ2. By the way, the loss of the surface acoustic wave resonator device is attributed to propagation loss, loss of mode conversion into bulk waves, etc., and diffraction loss. Considering the diffraction loss, the comb-shaped excitation electrode 17
When the surface wave excited by the wave propagates through the grating reflector 18, the surface wave leaks out of the reflector 18 to cause the resonator 13
It reduces the energy stored therein and lowers the unloaded Q factor, which is an indicator of resonator performance. As shown in Fig. 12, the unloaded Q value due to the above analysis loss depends on the width WL / λ of the grating reflector 18 normalized by the wavelength λ of the surface wave. It rapidly decreases with the decrease of λ. A decrease in the unloaded Q value means an increase in diffraction loss, which in turn leads to an increase in resonance loss. Therefore, by providing the above-mentioned relationship of WL ₁ / λ ₁ > WL ₂ / λ ₂ , the resonator 13 resonating at a high frequency has a diffractive loss of the surface acoustic wave more than the resonator 12 resonating at a low frequency. Will increase. Therefore, resonators that resonate at low frequencies
Resonator electrode 13 that resonates high frequency with resonance loss Ar1 of 12 13
The resonance loss Ar2 of can be set to a value close to the same. Therefore, when the surface acoustic wave resonator device of this embodiment is used to form an oscillation circuit, it is extremely easy to make the output levels from the resonator 12 and the resonator 13 close to the same level. Further, according to such a surface acoustic wave resonator device, since the electrode pattern can be easily formed by the method of forming the electrode pattern by a well-known technique, problems may occur in workability and yield. Therefore, the manufacturing cost can be reduced.

Next, a prototype example in which the present invention is applied to a surface acoustic wave resonator device used in an RF converter circuit of a video tape recorder will be described. This RF converter circuit outputs NTSC system, USA 3ch (61.25MHZ) and 4ch (67.25MHZ) carrier waves. Also, as the piezoelectric substrate of this surface acoustic wave resonator device, LiTaO3 of xcut-112 ° Y propagation is used, and both the excitation electrode and the reflector are made of aluminum film (lidge).
, And the value obtained by normalizing the width of the above reflector by wavelength is used as a resonator that resonates at low frequencies. WL1 / λ1 =
We set WL2 / λ2 = 7.8 for a resonator that resonates at a high frequency of 9.0. FIG. 3 shows the distribution of the resonance loss of this surface acoustic wave resonator device. As shown in the figure, it was confirmed that the resonance loss Ar1 of the resonator resonating at a low frequency and the resonance loss Ar2 of the resonator resonating at a high frequency have almost the same value.

It should be noted that according to the above-described embodiment, the above-mentioned normalized value is related between two different sets of resonators, but the present invention is not limited to this, and three or more sets of resonators are provided. The same can be done between the two.

[Advantages of the Invention] As described above, according to the surface acoustic wave device of the present invention,
The resonance loss can be set to the same value between the resonators having different resonance frequencies, and the manufacturing variation can be reduced and the manufacturing cost can be reduced.

[Brief description of drawings]

FIG. 1 is a front view showing a surface acoustic wave resonator device according to an embodiment of the present invention, FIG. 2 is a partially enlarged view of FIG. 1, and FIG. 3 is a prototype example of this surface acoustic wave resonator device. FIG. 4 shows the results, FIG. 4 is a front view showing a conventional surface acoustic wave resonator device, FIG. 5 is a longitudinal side view of FIG. 4, and FIG. 6 is a circuit diagram showing an equivalent circuit of FIG. 7 is a circuit diagram showing the impedance circuit of FIG. 4, FIG. 8 is a circuit diagram of the surface acoustic wave resonator device of FIG. 4 applied to a Colpitts oscillator circuit, and FIG. 9 is the impedance circuit of FIG. FIG. 10 is a circuit diagram for explaining the resonance loss of the surface acoustic wave resonator device of FIG. 4, and FIG. 11 is a diagram for explaining the resonance loss of a conventional surface acoustic wave resonator device having two resonator electrodes. FIG. 12 is a diagram for explaining the diffraction loss of the surface acoustic wave resonator device. 11 …… Piezoelectric substrate 12, 13 …… Resonator electrodes WL1, WL2 …… Aperture length

Claims (1)

[Claims] 1. A substrate for propagating a surface acoustic wave, an excitation electrode formed by intersecting a pair of comb-teeth electrodes formed on the substrate, and arranged on the substrate so as to sandwich the excitation electrode. A surface acoustic wave resonator comprising a plurality of surface acoustic wave resonators having different resonance frequencies, wherein the surface acoustic wave resonator resonates at a low frequency fr1. The value WL1 / λ1 obtained by dividing the grating reflector width WL1 of the wave resonator by the elastic surface wavelength λ1 of the low frequency, and the grating reflector width WL2 of the surface acoustic wave resonator resonating at the high frequency fr2.
Value divided by the high frequency surface acoustic wave wavelength λ2 WL2 /
A surface acoustic wave resonator device characterized in that the relationship with λ2 is WL1 / λ1> WL2 / λ2 and WL2 / λ2 <10.