JP2526294Y2 - Surface acoustic wave device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a surface acoustic wave device having high withstand power.

(Prior Art) FIG. 2 is a schematic plan view showing an example of a conventional surface acoustic wave device having a multi-transducer configuration, in which interdigital electrode fingers are combined on a piezoelectric substrate 1 so as to face each other. A plurality of input-side surface acoustic wave converters (hereinafter, referred to as input-side converters) 2-1 to convert the input and input electric signals into surface acoustic waves
A plurality of output surface acoustic wave converters (hereinafter, referred to as “surface acoustic wave converters”) configured by combining 2-5 and interdigital electrode fingers facing each other and receiving surface acoustic waves excited by each input side transducer and converting the surface acoustic waves into electric signals. , Output side converter) 3-1 to 3-6,
One end of each of the input-side converters 2-1 to 2-5 is connected to the input-side common bus electrode 10 alternately in the propagation direction of the surface acoustic wave, and the input terminal 4 is connected via the input-side common bus electrode 10. , And the other end is grounded.
One end of -6 is connected to the output-side common bus electrode 11, further connected to the output terminal 5 via the output-side common bus electrode 11, and the other end is grounded.

The electric signal supplied to the input terminal 4 is distributed to each of the input converters 2-1 to 2-5 through the input common bus electrode 10, and each of the input converters 2-1 to 2-5 includes a piezoelectric substrate. Excitation of a surface acoustic wave on 1 This surface acoustic wave propagates to both sides of each of the input-side converters 2-1 to 2-5 in a direction perpendicular to the electrode fingers. The surface acoustic waves are output from the respective output-side converters 3-1 to 3-6.
, A potential difference is generated between the electrode fingers, and the potential difference is extracted as an electric signal from the output terminal 5 through the output-side common bus electrode 11.

In the surface acoustic wave device shown in FIG. 2, when an electric signal is supplied from the output terminal 5, the electric signal can be extracted from the input terminal 4 in the same manner as the above-described operation. In this case, the output converters 3-1 to 3- in FIG.
6 operates as an input side converter, and the input side converters 2-1 to 2-1.
2-5 operates as an output side converter.

(Problem to be Solved by the Invention) However, in the surface acoustic wave device having the above-described configuration, the input-side converters 2-1 to 2-1 have an impedance of 50Ω when the element is viewed from the input terminal 4 and the output terminal 5. 2-
The line width of the input-side common bus electrode 10 connecting the terminal 5 to the input terminal 4 and the line width of the output-side common bus electrode 11 connecting the output-side converters 3-1 to 3-6 and the output terminal 5 are limited. The line width is a function of the thickness of the piezoelectric substrate 1 and its dielectric constant. For example, in the case of a 0.35 mm-thick LiTaO ₃ substrate, the line width is about 40 μm.

On the other hand, since the power distributed to each input-side converter is equal, the current flowing through the input-side common bus electrode is partially different. For example, in FIG. 2, the current at point a of the input-side common bus electrode 10 is twice the current at point b, and the current at point c of the output-side common bus electrode 11 is three times the current at point d. .

Therefore, a portion where a large amount of current flows easily melts.

That is, the power that can be applied to the surface acoustic wave device is limited by the dissolution of a part of the input-side or output-side common bus electrode whose line width is determined to obtain a predetermined impedance,
There is a drawback that it is impossible to supply high power.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface acoustic wave device that eliminates the above-described drawback that high power cannot be supplied and improves power durability.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a piezoelectric substrate in which interdigitated electrode fingers are combined to face each other, and converts an input electric signal into a surface acoustic wave. A plurality of input-side surface acoustic wave transducers to be converted and interdigital electrode fingers are combined to face each other, and receive the surface acoustic waves excited by each of the input-side surface acoustic wave converters to convert them into electric signals. A plurality of output surface acoustic wave converters,
The input side surface acoustic wave converters are alternately arranged in the propagation direction of the surface acoustic wave, one end of each input side surface acoustic wave converter is connected to the input side common bus electrode, and the other end is connected to the input terminal via the input side common bus electrode. A multi-converter configuration in which each output side surface acoustic wave converter is grounded, one end of each output side surface acoustic wave converter is connected to an output side common bus electrode, and further connected to an output terminal via the output side common bus electrode, and the other end is grounded. In the surface acoustic wave device of (1), a line width of a portion of the input-side common bus electrode near the input terminal or a portion of the output-side common bus electrode near the output terminal is widened.

(Operation) The electric signal supplied to the input terminal is distributed to each input-side surface acoustic wave converter through the input-side common bus electrode. In this case, a large current flows in a portion of the input-side common bus electrode close to the input terminal, but since the line width of the portion is widened, an increase in current density is suppressed.

In addition, since the signal current of each output-side surface acoustic wave converter is collected at the output terminal through the output-side common bus electrode, a large current flows in a portion near the output terminal. However, also in this case, since the line width of the portion near the output terminal of the output-side common bus electrode is increased, the increase in current density is suppressed.

Therefore, the power durability of the surface acoustic wave device according to the present invention is improved.

(Embodiment) FIG. 1 is a schematic plan view showing an embodiment of a surface acoustic wave device having a multi-converter structure according to the present invention. In FIG. 1, a piezoelectric substrate 1, an input-side surface acoustic wave converter (hereinafter, referred to as an input-side converter) 2-1 to 2-5, and an output-side surface acoustic wave converter (hereinafter, referred to as an output-side converter). ) 3-1 to 3-
6, the input terminal 4, the output terminal 5, etc. are the same as those given the same numbers as shown in FIG. 2 and the arrangement is also the same, but the input at one end of each of the input side converters 2-1 to 2-5. The line width of a portion 8 of the input-side common bus electrode 6 connecting the terminal 4 between the input terminal 4 and the input-side converter 2-2, 2-3, 2-4 closest to the input terminal 4 The output terminal 5 of the output-side common bus electrode 7 connecting one end of each of the output-side converters 3-1 to 3-6 and the output terminal 5 and the output-side converter 3-
The line width of the portion 9 between 3, 3 and 4 is widened.

The line width of the input common bus electrode 6 in FIG.
m, when the line width of the portion 8 near the input terminal 4 is 60 μm, inputting 1 W of power to the input terminal 4
Is I = (P / Z) ^1/2 = (1/50) ^1/2 = 0.1414 (A), and each input-side converter 2-1 to 2-5 has I ′ = I / 5 = 0.1414 / 5 = 0.02828 (A). Accordingly, the current I ₈ flowing in the input side common bus current I ₆ flowing through the electrode 6, closer to the input terminal portion 8, _{respectively, I 6 = 0.02828 (A)} , I 8 = I 6 × 2 = 0.05656 (A) and Become. Dissolution of the electrodes is caused by heat generated by the electrode resistance. If the line width (a) of the portion ₈ where the current I ₈ flows is 40 μm, the film thickness (b) is 5000 °, the resistivity (ρ) is 2.4 × 10 ⁻⁸ Ω · cm, and the length (C) is 1 mm. Then, the resistance R becomes Since the energy E to be heat in this portion becomes ^{_{E = RI 8 2 = 3.839 ×}} 10 -5 (J). It is assumed that the electrode is melted by this energy. The line width of the portion 8 close to the input terminal 4 should be 40 μm to 60 μm.
Upon spreading, because the electrode resistance is reduced to 2/3, the maximum current that can flow to the electrodes of the current I ₈ Double. Therefore, the power that can be supplied to the input terminal 4 is 3/2
And the power durability is improved.

On the other hand, the input impedance at the input terminal 4 and the output terminal 5 fluctuates due to an increase in the line width of a part of the input-side and output-side common bus electrodes. However, the variation is in an acceptable range. For example, five input converters and six output converters
According to the actual measurement of a surface acoustic wave device composed of a total of 11 surface acoustic wave converters, the input impedance (R is a real part, × is an imaginary part) when the input and output common bus electrodes are all 40 μm. ) Is 47.5 for the passband signal.
Although Ω <R <53.0Ω and −5.3Ω <× <−2.6Ω, the input impedance when the input-side common bus electrode near the input terminal is extended to 60 μm by adopting the present invention is 46.0Ω.
<R <49.0Ω, −5.8 <× <−3.4Ω, and the change in impedance is within an allowable range. The return loss, which is a measure to measure the degree of impedance mismatch, is 10 dB or more with respect to the signal in the filter pass band, and no impedance mismatch occurs. The same can be said for the case where the portion of the output-side common bus electrode near the output terminal is expanded.

In addition, in the surface acoustic wave device including the above-described 11 surface acoustic wave converters, even when the input power of 2 W is supplied, the input or output common bus electrode is not melted, and the power durability is clearly improved. . In the above-described embodiment, both the line width of the portion of the input-side common bus electrode near the input terminal and the line width of the portion of the output-side common bus electrode near the output terminal are shown. Enlarging the line width on one side can also contribute to improving the power durability.

(Effects of the Invention As described in detail above, according to the present invention, in a surface acoustic wave device having a multi-transducer configuration, the input or output common bus electrode close to the input / output terminal where the current density is highest is obtained. Since the line width has been increased, the current density can be reduced,
Power durability is improved.

According to the present invention, it has become possible to apply a surface acoustic wave device to a system that handles power in the order of watts, which was conventionally said to be impossible to apply the surface acoustic wave device.

[Brief description of the drawings]

FIG. 1 is a schematic plan view showing an embodiment of the present invention, and FIG. 2 is a schematic plan view of a conventional surface acoustic wave device. DESCRIPTION OF SYMBOLS 1 ... Piezoelectric substrate, 2-1 to 2-5 ... Input surface acoustic wave converter, 3-1 to 3-6 ... Output surface acoustic wave converter, 4 ... Input terminal, 5 ... Output terminal, 6 ... Input Side common bus electrode, 7 ...
Output common bus electrode.

Claims (1)

(57) [Scope of request for utility model registration] 1. A plurality of input-side surface acoustic wave converters, each of which is formed by combining interdigital electrode fingers on a piezoelectric substrate and converts an input electric signal into a surface acoustic wave;
A plurality of output surface acoustic wave converters, which are configured by interdigitated electrode fingers facing each other and receive surface acoustic waves excited by the input surface acoustic wave converters and convert the surface acoustic waves into electrical signals, The input side surface acoustic wave converters are alternately arranged in the propagation direction of the surface acoustic wave, one end of each input side surface acoustic wave converter is connected to the input side common bus electrode, and the other end is connected to the input terminal via the input side common bus electrode. A multi-converter configuration in which each output side surface acoustic wave converter is grounded, one end of each output side surface acoustic wave converter is connected to an output side common bus electrode, and further connected to an output terminal via the output side common bus electrode, and the other end is grounded. The surface acoustic wave device according to claim 1, wherein a line width of a portion of the input-side common bus electrode near the input terminal or a portion of the output-side common bus electrode near the output terminal is widened.