JPS62189809A - Two-port surface acoustic wave resonator - Google Patents

Abstract

PURPOSE:To prevent the deterioration in the frequency characteristic even with high power excited by arranging the minimum length of an active electrode finger of a weighted interdigital electrode so as to allow it to come most inside. CONSTITUTION:Two sets of weighted interdigital electrodes 2 are arranged to a piezoelectric substrate 1 at a prescribed interval. A reflecting electrode 3 is provided at both sides of the electrode 2. The electrode 2 is selected to that the active electrode finger 21 near the electrode 3 is longer and the length of the electrode fingers 21 toward the center of the substrate 1 is shorter. In applying an electric signal to the electrode 2, a surface wave of a prescribed frequency is excited. Then the electrode finger 21 comparatively longer is arranged at a part subject to less distortion, then a voltage caused in the substrate 1 is low and the joule heat is comparatively small. Thus, the deterioration in the frequency characteristic is prevented even when the resonator is excited by a high power.

Description

[Detailed description of the invention] [Industrial application field].

The present invention relates to a two-port surface acoustic wave resonator.

[Conventional technology]

FIGS. 2 and 3 show schematic configuration diagrams of a two-port surface acoustic wave resonator that has been commonly used in the past.

Each of these two-port surface acoustic wave resonators consists of a piezoelectric substrate 1, two sets of weighted interdigital electrodes 2 arranged at a predetermined interval on the top surface of the piezoelectric substrate 1, and reflective electrodes provided on both sides of the piezoelectric substrate 1, sandwiching them between the weighted interdigital electrodes 2. It is composed of an electrode 3. Each weighted interdigital electrode 2 has a pair of active and active electrode fingers formed to interlock with each other. When a predetermined electrical signal is applied to the pair of active electrode fingers, the piezoelectric substrate vibrates and a surface wave of a predetermined frequency is excited. The characteristics such as the frequency of this surface wave are determined by the interval between each active electrode finger 210 and the like. In addition to operating as a so-called SAW resonator, such a two-port surface acoustic wave resonator also operates as a two-port surface acoustic wave resonator.
It is also used as a delay filter by propagating surface waves between the set of weighted interdigital electrodes 2.2.

Now, the crossing length D (FIG. 2) of each of the active electrode fingers 21 is selected to be approximately 100 times the wavelength of the propagating surface wave for the purpose of dispersing the input power.

However, in this case, surface waves in a direction different from the intended propagation direction of the surface waves (arrow 4 direction), so-called transverse mode spurious, are generated. In order to suppress this transverse mode spurious, the lengths of the active electrode fingers 21 are usually selected to have different specific lengths, and so-called weighting is performed.

In the case of the two-port surface acoustic wave resonator shown in FIG. 2, the active electrode fingers on the right side of the figure are weighted so that their lengths are shortened, as indicated by the broken line 51. In addition, in the case of the one in FIG. 3, the active electrode fingers 21 of the interdigital electrodes 2
are weighted so that the inner ones have longer lengths.

In addition, so-called grating reflective electrodes 3 are provided to sandwich the two sets of weighted interdigital electrodes 2 so that only surface waves of a predetermined frequency are excited on the piezoelectric substrate 1.

[Problem that the invention seeks to solve]

In such a two-bottom surface acoustic wave resonator, when a surface wave is excited, the amount of displacement that occurs on the surface layer of the piezoelectric substrate 1 usually has a distribution as shown in FIG.

That is, the amount of displacement is maximum at the center of the substrate 1 and becomes smaller toward both sides thereof.

As described above, when the strain of the piezoelectric substrate 1 is concentrated in the center, a relatively high voltage is generated in this portion due to the piezoelectric effect. Since active electrode fingers have a certain electrical resistance,
The voltage thus generated causes a predetermined current to flow, generating Joule heat.

When a two-port surface acoustic wave resonator is excited with high power, the electrode fingers near the center of the piezoelectric substrate generate enough heat to cause thermal deterioration, and are destroyed due to deformation, peeling, etc. There is. The breakage of the active electrode finger is particularly visible in the area surrounded by the broken line 6 in FIGS. 2 and 3.

During normal operation, for example, 500MHz to 700M
A two-bottom surface acoustic wave resonator in the Hz band has frequency characteristics as shown by the solid line 10 in FIG.

However, when the active electrode fingers are destroyed as described above, spurious waves as shown by the broken line 11 are generated, the main vibration is inhibited, and there is a possibility that the SAW resonator will no longer function.

The present invention has been made with attention to the above points, and an object of the present invention is to provide a two-bottom surface acoustic wave resonator whose frequency characteristics do not deteriorate even when excited with high power.

[Means for solving problems]

The two-port surface acoustic wave resonator of the present invention includes a piezoelectric substrate;
It consists of two sets of weighted interdigital electrodes arranged at a predetermined interval on the upper surface, and reflective electrodes provided on both sides of the electrodes sandwiching them, and each of the two sets of weighted interdigital electrodes has a weighted interdigital electrode. The device is characterized in that it has a plurality of active electrode fingers whose lengths are selected according to the length of the active electrode fingers, and that the active electrode fingers with the minimum length are arranged so as to be located at the innermost position.

[Effect]

In this manner, in the two-port surface acoustic wave resonator of the present invention, the short active electrode fingers are arranged at the innermost position, that is, at the side closest to the center of the piezoelectric substrate.

As a result, a relatively large voltage generated near the center of the piezoelectric substrate is applied to the short active electrode fingers.

The Joule heat generated as a result becomes smaller as the length of the active electrode finger becomes shorter, and does not generate enough heat to cause thermal deterioration.

Therefore, the two-port surface acoustic wave resonator of the present invention is unlikely to cause deterioration of the active electrode fingers even when excited with high power.
It is possible to maintain good frequency characteristics.

〔Example〕

FIG. 1 is a schematic diagram of a two-port surface acoustic wave resonator of the present invention.

In the figure, on the piezoelectric substrate 1, there are two
A set of weighted interdigital electrodes 2 is arranged. Reflective electrodes 3 are provided on both sides of the weighted interdigital electrode 2.

Each weighted interdigital electrode 2 is composed of a pair of active electrode finger groups 21 .

In each weighted interdigital electrode 2, the active electrode finger 21 on the side closer to the reflective electrode 3 is longer, and the active electrode finger 21 on the side closer to the center of the piezoelectric substrate 1 is shorter in length. has been selected. The weighted interdigital electrodes 2 as a whole are weighted as indicated by broken lines 5 in the figure.

That is, all weighted interdigital electrodes 2 are arranged so that the innermost active electrode fingers 21 (on the side facing the center of the piezoelectric substrate) are the shortest.

In such a two-port surface acoustic wave resonator, when an electric signal is applied to the weighted interdigital electrodes 2, a surface wave of a predetermined frequency is excited. Due to this surface wave, the surface layer of the piezoelectric substrate 10 vibrates with a displacement distribution such that the largest strain is concentrated at the center, as shown in FIG.

At this time, since the smallest length of the active electrode fingers 21 is placed in the part that vibrates with the greatest strain, the voltage generated in the piezoelectric substrate 1 causes a current to flow through the active electrode fingers 21. Even if it flows, it generates relatively little heat.

On the other hand, since the relatively long active electrode fingers 21 are arranged in areas with small strain, the voltage generated on the piezoelectric substrate 1 is also low, and the Joule heat is relatively small.

As a result of the above, even if this two-bottom surface acoustic wave resonator is excited with high power, each active electrode finger 21 generates little heat and there is no risk of deterioration.

Therefore, highly reliable and stable characteristics can be maintained even at high power.

[Modified example]

The two-port surface acoustic wave resonator of the present invention is not limited to the above embodiments.

The configuration of the weighting pattern, the number of active electrode fingers, the spacing, etc. can be arbitrarily selected depending on the purpose of the resonator and the required characteristics.

〔Effect of the invention〕

Since the two-port surface acoustic wave resonator of the present invention described above is unlikely to cause deterioration of the active electrode fingers, it can be used as a high-power SAW resonator that excites with high power.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a two-port surface acoustic wave resonator of the present invention, and FIGS. 2 and 3 are schematic configuration diagrams showing an example of a conventional two-port surface acoustic wave resonator. , FIG. 4 is a graph showing its displacement distribution, and FIG. 5 is a graph showing its frequency characteristics. 1... Piezoelectric material, 2... Weighted interdigital electrode, 3...
Reflective electrode, 21...Active electrode finger. Applicant: NEC Corporation Representative

Claims (1)

[Claims] It consists of a piezoelectric substrate, two sets of weighted interdigital electrodes arranged at a predetermined interval on the upper surface thereof, and reflective electrodes provided on both sides of the piezoelectric substrate, sandwiching them between the two sets of weighted interdigital electrodes. The electrode has a plurality of active electrode fingers each having a length selected according to weighting, and is arranged such that the shortest length of the active electrode fingers is located at the innermost position. 2-port surface acoustic wave resonator.