JPS6110309A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To improve the acoustic reflection at the end by arranging an electrode of 1/8 wavelength width having nearly half the aperture length to one of input/output transducers while facing the other transducer. CONSTITUTION:The input transducer 41 and the output transducer 42 formed to a piezoelectric substrate 40 are formed in a way that the 1st split 1/8 wavelength width electrode fingers 411, 421 and the 2nd electrode fingers 412, 422 mesh with each other. Further, an electrode 43 of 1/8 wavelength width of nearly half the aperture length is arranged with an air gap of 1/8 wavelength to the transducer 41 while facing the transducer 42 and a sound absorbing agent 44 is coated to the upper part of dummy electrodes 414, 415, prolonged toward the end face of the substrate 40. On the other hand, an acoustic impedance compensating electrode 46 is arranged on a propagation path of the transducer 42. Thus, the acoustic reflection at the end is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a surface acoustic wave device with improved acoustic reflection noise.

[Technical background of the invention and its problems] A t-polar pair is formed by interlocking a first comb-shaped electrode finger and a second comb-shaped electrode finger on a piezoelectric substrate, thereby forming an elastic surface. 2. Description of the Related Art Surface acoustic wave devices configured as transducers are known. FIG. 3 shows the structure of a basic transducer of this type. In the figure, an input/output transducer 2 and three output transducers formed on a piezoelectric substrate 1 each have a split-type first electrode finger 4.5 and a second split-type electrode finger each having two electrode fingers each having a wavelength width of 17B. Electrode finger7.
8 are interlocked with each other. The space 1jJ9, 10 between each electrode finger is 1/8, which is the same as the width of each 11 electrode finger.
wavelength. In a transducer with such an electrode finger structure, as described in the specification of U.S. Pat. No. 3,727,155, both ends of each electrode finger are It is known that reflections of surface acoustic waves generated by the electrode fingers cancel each other out due to reflections from adjacent electrode fingers. However, even if a surface acoustic wave filter is configured with a transducer having a structure in which the synthesized wave of internal acoustic reflections becomes zero, there is still the following problem that must be solved.

In other words, as mentioned above, the acoustic impedance is different between the location where the electrode finger is present and the location where the electrode finger is not present, so acoustic reflection occurs at both ends of the electrode finger, but similarly, acoustic reflection occurs at both ends of the electrode finger. Since there is a difference in acoustic impedance between the two ends of the transducer, acoustic reflections also occur at both ends of the transducer. Therefore,
As a means to eliminate such acoustic reflection, as shown in FIG. 4, an electrode 20 having the same shape as the electrode finger of the input/output transducer in the propagation path of the surface acoustic wave is arranged so as to match the period of the acoustic impedance of the input/output transducer. The surface acoustic wave device installed in the 1972 IBEE Ultra
sonica symposium PP373-37
It was reported in 6.

However, with such means, for example, in a surface acoustic wave device having a structure in which the input fluid transducer 31 is aboded as shown in FIG. 5, the following disadvantages occur. In other words, the signal supply side dummy electrodes 32 and 33 of the input quadrature transducer 31 and the acoustic impedance compensation electrodes 34 and 35 of the surface acoustic wave propagation path adjacent to each other with a gap of 1/8 wavelength from the ends of these electrodes are connected. Due to the IL magnetic coupling, surface waves 36 and 37 are radiated in the area where the two face each other. Such surface waves cause deterioration of desired frequency characteristics. Therefore, in a surface acoustic wave device having an avocized transducer, a structure is desired that can improve acoustic reflection at the end of the transducer and does not cause surface wave radiation.

[Object of the Invention] The present invention has been made in view of the above points, and is an object of the present invention to provide a surface acoustic wave device that improves acoustic reflection at the end of an input/output transducer and does not radiate surface waves. .

[Summary of the Invention] The present invention comprises disposing an electrode having a width of 1/8 wavelength and approximately half the aperture length on either one of the input and output transducers, facing the other transducer, and connecting the transducer and the piezoelectric material. The acoustic impedance of the propagation path of surface acoustic waves between the sound absorbing materials formed in the direction of the end surface of the substrate is compensated by the electrodes.

[Effects of the Invention] According to the present invention, acoustic reflection at the end of the transducer can be improved in an elastic surface having an avocized transducer, and radiation of surface waves can be prevented from occurring. .

[Embodiments of the invention] Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which a piezoelectric substrate 4
0, an input juicer 41 and an output juicer 42 are formed. Inlet juicer 41
The output reducer 42 has a shape in which split-type first electrode fingers 411, 421 and second electrode fingers 412, 422, each having a 1/8 wavelength width, are engaged with each other. And the space between each electrode finger @ 413, 4
23 is 1/8 wavelength, which is the same as the width of each electrode finger.

In addition, the right end part 1 of the input fluid juicer 41 in the drawing is
1/8 of the length of approximately half the aperture length with a gap of 1/8 wavelength.
An electrode 43 having a width of 8 wavelengths (1/8λ: wavelength) is placed facing the output transducer 42, and the dummy electrodes 414 and 415 of the input transducer 41 extend toward the end surface of the piezoelectric substrate 40. On the other hand, the upper parts of these parts (: are those coated with sound absorbing material 44), while the output juicer 42
The propagation path on the right side of the drawing (- indicates that an acoustic impedance compensation electrode 46 is arranged, and the adjacent electrodes are mutually grounded.

Acoustic reflections at both ends of a transducer of such a structure can be suppressed as described below. For example, among the surface acoustic waves 45-a and 46-b bidirectionally excited from the input quadrature transducer 41, the surface acoustic wave 46-at' traveling toward the left side of the drawing; Since there is no place where the acoustic impedance changes significantly, there is no reflection. On the other hand, the surface wave 46-b traveling toward the output juicer 42 side is
Since there is a large change in acoustic impedance at the right end of the input quadrature transducer 41 in the figure, a portion of the acoustic impedance is reflected, generating reflected waves 47-1 and 47-b. However, since the phases of these reflected waves 47-1 and 47-b are opposite to each other, the reflected waves 47-1 and 47-b are not received by the input quadrature transducer 41, but proceed toward the sound absorbing material shrine, and are absorbed. In addition, the surface acoustic wave which was not reflected at the right end of the input juicer 41 and proceeded toward the output juicer 42 has a 47-0° 47
Since there is a large change in acoustic impedance at the left end of the output juicer 420 in the figure, a portion of the −d is partially reflected and travels toward the input juicer 41.

A part of the surface wave is reflected again and returns, but since the phases of both reflected waves 47-C and 47-d are opposite to each other, they proceed toward the sound absorbing material 45 without being received by the output transducer 42. do. Moreover, these reflected waves 47-C, 4
7-d does not reflect because there is no place where the acoustic impedance changes significantly in the section before being absorbed by the sound absorbing material 44-b.

Further, in the embodiment of the present invention, since there is no ground electrode in X contact with the signal supply side electrode of the input quadrature transducer, surface wave radiation does not occur as in a transducer with a conventional structure.

As described above, the transducer structure of the surface acoustic wave device of the present invention has the advantage that acoustic reflection at both ends of the input/output transducer can be improved, and at the same time, surface wave radiation does not occur at both ends of the avocized transducer.

[Other embodiments of the invention] FIG. 2 shows another structural embodiment of the invention.

In this example, the present invention is applied to a structure in which the split-type electrode fingers of the input and output juicer 51 and the output juicer 52 are interlocked with each other with a constant intersecting width. In this structure, the input fluid juicer 5
An acoustic impedance compensation electrode 53 is disposed on the propagation path on the left side of the drawing in Figure 1, and a sound absorbing material 54 is applied on top of the electrode 53.

At the right end of the drawing of the input fluid juicer 51, there is a 1/
56 1/s wavelength width electrodes having a length approximately half the aperture length are arranged with a gap of s wavelength. On the other hand, an acoustic impedance compensating electrode 54 is arranged on the propagation path on the right end side of the circuit of the output transducer 52, and a sound absorbing material 55 is applied on the upper part.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, FIG. 2 is a diagram showing another embodiment of the present invention, FIG. 3 is a diagram showing the configuration of a conventional surface acoustic wave device, and FIGS. FIG. 5 is a diagram showing a conventional surface acoustic wave device that compensates for the acoustic impedance of the surface acoustic wave propagation path. 40...Piezoelectric substrate 41...Input juicer 411...Split type first electrode finger 412/Split type second electrode finger 413, 414...Dummy electrode 12...Output juicer 421...Split type first electrode finger 422...Split type thread 211 pole finger 4t...1/s
Wavelength width electrode 44.45...Sound absorber Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 4 2ρ Fig. 5 = 9

Claims (3)

[Claims] (1) In a surface acoustic wave device in which a surface acoustic wave input/output transducer is formed on a piezoelectric substrate, a gap of 1/8 wavelength is placed from the end of one of the input/output transducers. A surface acoustic wave device characterized in that a 1/8 wavelength electrode having a length approximately half the aperture width of the transducer is disposed facing the other transducer. (2) The elastic surface according to claim 1, characterized in that the periodic structure of acoustic impedance inside the input/output transducer matches the periodic structure of acoustic impedance of the surface wave propagation path in the direction of the end surface of the piezoelectric substrate. wave device. (3) The surface acoustic wave device according to claim 1, wherein the electrode fingers constituting the input/output transducer section are split-type electrodes with a width of 1/8 wavelength.