JP2560995B2 - Surface acoustic wave device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a longitudinal mode resonator type surface acoustic wave device, and more particularly to a surface acoustic wave device having a reflector for confining surface acoustic wave energy.

[0002]

2. Description of the Related Art In a conventional longitudinal mode resonator type surface acoustic wave device, an input / output interdigital electrode and a reflection for confining excited surface acoustic wave energy provided on both sides of the interdigital electrode. And the opening length of the reflector is the same as the opening length (crossing width) of the interdigitated electrodes. In this surface acoustic wave device, higher-order transverse modes are excited in the direction perpendicular to the surface acoustic wave propagation direction. The excitation of this higher-order transverse mode differs depending on the propagation path width of the surface acoustic wave (aperture length of the interdigital electrode). If it is small, the higher-order component is cut off, and only the lower-order mode is excited. It is known that higher-order transverse modes are also excited. Therefore, in the design, the opening length of the interdigitated electrode is made as small as possible so that a plurality of higher-order transverse modes (higher-order transverse modes appear as spurious in resonance characteristics) are not excited. As a method of suppressing higher-order transverse mode spurs, the shape of the envelope connecting the midpoints of the end sides of the strip rows forming the reflector is made non-linear, and the transverse mode spurious is suppressed by diffuse reflection. There is a way.
For example, as disclosed in Japanese Patent Laid-Open No. 59-200519 (see FIG. 4), regarding the shape of the reflector 13 ′,
The shape of the envelope connecting the midpoints of the ends of the strip rows 13'-1 to 13'-n is made non-linear, and the transverse mode spurious is diffused and suppressed.

[0003]

However, according to such a conventional surface acoustic wave device, it is necessary to design the opening length of the interdigitated electrode as small as possible so that a plurality of higher-order transverse modes are not excited. However, the degree of freedom in design was limited. Further, in the method of suppressing the lateral mode spurious by irregularly reflecting the shape of the envelope connecting the midpoints of the end sides of the tip ends of the strips of the reflector, the shape of the reflector pattern becomes complicated and mask fabrication is difficult. In some cases, it is difficult to cause the yield at the time of film formation to be deteriorated, or a part of the irregularly reflected waves may be incident on the output interdigitated electrode again and the characteristics may be deteriorated.

The present invention has been made in order to solve such a problem, and an object thereof is to suppress the opening length of the interdigitated electrodes to be small and to reduce the yield during film formation. An object of the present invention is to provide a surface acoustic wave device capable of suppressing high-order transverse mode spurious without causing deterioration of characteristics.

[0005]

In order to achieve such an object, the present invention provides a surface acoustic wave device as described above, wherein the aperture length of the reflector is 70% or less of the aperture length of the interdigital electrode. It is what In addition, the interdigital electrode is
E-shaped first electrode and E intersecting this with a predetermined gap
A second electrode having a V-shape, and the tip of the first electrode and the second electrode
The distance from the tip of the electrode is the opening length of the interdigital electrode.
It is something.

[0006]

According to the present invention, therefore, the shape of the third-order transverse mode excited by the interdigitated electrodes and the shape of the third-order transverse mode that may exist in the reflector are significantly different from each other. It becomes difficult for mode conversion in the horizontal mode to occur.

[0007]

EXAMPLES The present invention will now be described in detail based on examples. FIG. 1 is a plan view of a longitudinal mode resonator type surface acoustic wave device showing an embodiment of the present invention. In the figure, 11
Is a piezoelectric substrate, 12 is an interdigital finger electrode for input and output, 13, 1
Reference numeral 3 is a reflector provided on both sides of the interdigital electrode 12. Further, a is the opening length of the interdigital electrode 12, and b is the opening length of the reflector 13. In this embodiment, the aperture length b of the reflector 13 is 70% of the aperture length a of the interdigital electrode 12 [(b
/ A) × 100%].

In this surface acoustic wave device, the surface acoustic wave excited from the interdigital electrode 12 is reflected by the reflectors 13 and 13.
And the surface wave energy is confined in the reflectors 13 and 13 and a resonance characteristic is obtained. At this time, since the opening length a of the interdigital electrode 12 is constant, a plurality of transverse modes 31 are generated in the direction perpendicular to the surface acoustic wave propagation direction, as shown in FIG. 1st order, 3rd order and 5th order are shown). Of these transverse modes 31, the higher-order modes of the third order and higher are spurious in frequency characteristics. In particular, the third-order transverse mode is a commonly used aperture length width, which causes a problem. Further, the transverse mode excited by the interdigital electrode 12 is mode-converted into the transverse mode that can exist in the reflectors 13, 13.

At this time, assuming that the opening length a of the interdigitated electrode 12 and the opening length a of the reflector 13 are equal, each mode is converted into the same energy distribution shape, so that inside the reflectors 13 and 13. But it is converted to the same transverse mode with the same shape.

However, in this embodiment, the reflector 1
The opening length b of 3 and 13 is 7 of the opening length a of the interdigital electrode 12.
It is set to 0%. That is, in the present embodiment, the peak width c (see FIG. 2) of the third-order transverse mode, which is usually a problem, and the aperture length b of the reflectors 13 and 13 are made to substantially coincide with each other and are excited by the interdigital electrode 12. The shape of the third-order transverse mode and the shape of the third-order transverse mode that may exist in the reflectors 13 and 13 are greatly different from each other, so that mode conversion of higher-order transverse modes of the third order and higher is less likely to occur, and the reflector 13 , 13 to suppress higher-order transverse modes.

The peak width c of the third-order lateral mode in FIG. 2 is 67% (= 2/3) of the opening length a of the interdigital electrode 12, but the energy leaks and spreads a little in the higher-order mode.
It is effective that the aperture length b of the reflectors 13 and 13 is 70%, and when the aperture length b is 70% or less, there is a great effect on the higher-order transverse modes.

FIG. 3 is a plan view of a surface acoustic wave device showing another embodiment of the present invention, in which a reflector open type metal grating is provided. Also in this case, as in the case of FIG. 1, the opening length b of the reflectors 23, 23 is set to 70% or 70% or less of the opening length a of the interdigital electrode 22.

[0013]

As is apparent from the above description, according to the present invention, since the aperture length of the reflector is set to 70% or less of the aperture length of the interdigital electrode, it is excited by the interdigital electrode. The shape of the third-order transverse mode that differs from the shape of the third-order transverse mode that may exist in the reflector is greatly different, and the aperture length of the interdigital electrode is not suppressed to a small value, and the yield during film formation deteriorates Higher-order transverse mode spurious can be suppressed without deteriorating the characteristics.

[Brief description of drawings]

FIG. 1 is a plan view of a longitudinal mode resonance type surface acoustic wave device showing an embodiment of the present invention.

FIG. 2 is a diagram illustrating a transverse mode generated in this surface acoustic wave device.

FIG. 3 is a plan view of a surface acoustic wave device showing another embodiment of the present invention.

FIG. 4 is a diagram showing a shape of a reflector in a conventional surface acoustic wave device.

[Explanation of symbols]

 11 Piezoelectric Substrate 12 Interdigitated Electrode 13 Reflector 31 Transverse Mode a Interdigitated Electrode Aperture Length b Reflector Aperture Length c Third Transverse Mode Peak Width

Claims (2)

(57) [Claims] 1. A surface acoustic wave device comprising an input / output interdigitated electrode and reflectors provided on both sides of the interdigitated electrode for confining excited surface acoustic wave energy on a piezoelectric substrate. In, the opening length of the reflector is 70 times the opening length of the interdigitated electrode.
The surface acoustic wave device is characterized in that the ratio is less than or equal to%. 2. The crossed finger-shaped electrode according to claim 1, wherein the interdigitated electrode is a U-shaped first electrode and a predetermined shape.
It consists of an E-shaped second electrode that intersects with a gap,
The distance between the tip of the first electrode and the tip of the second electrode intersects.
Surface acoustic wave characterized by the aperture length of the forefinger electrode
apparatus.