JPH06350383A - Surface acoustic wave resonator - Google Patents

Abstract

PURPOSE:To suppress spurious response by providing a part of short-circuited electrode fingers to a part through which a surface acoustic wave passing through a gap of electrode fingers of an interdigital electrode transducer passes so as to uniformize the propagation condition of the surface acoustic wave. CONSTITUTION:A short-circuit part 7 is provided between electrode fingers adjacent a gap 6 provided to electrode fingers 5 of an interdigital electrode transducer(IDT) 2 on a piezoelectric substrate 1. The short-circuit part 7 is provided to have the same width as that of the gap 6 between electrode fingers through which surface acoustic waves A, C or the like pass when the arrangement shape of the gap 6 is weighted so as to be symmetrical horizontally around a line tying connection terminals 3, 4. Thus, the propagation condition of surface acoustic waves A, B, C is totally equal in the IDTs and the surface acoustic wave propagation condition of the entire IDTs is uniformized and spurious response is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave resonator used in a communication device, and more particularly to a surface acoustic wave resonator having a weighted interdigital transducer formed on a piezoelectric substrate. Is.

[0002]

^2. Description of the Related Art As a typical example, a Love wave (SH) whose electromechanical coupling coefficient (K ² ) is significantly larger than that of a Rayleigh wave type surface acoustic wave (P + SV wave).
The (wave) type surface acoustic wave resonator will be described. FIG. 2A is a plan view showing a configuration example of a Love wave type surface acoustic wave resonator, and FIG. 2B is a partial enlarged view of a portion 8 surrounded by a solid line in FIG. In FIG. 2, reference numeral 1 is a piezoelectric substrate, and 12 is an interdigital transducer.
sducer (hereinafter abbreviated as IDT)), 3 and 4 denote connection terminals. The Love wave type surface acoustic wave resonator shown in FIG.
On a piezoelectric substrate 1 such as a LiNbO ₃ (lithium niobate) rotating Y plate, gold (Au), silver (Ag), platinum (Pt)
By attaching an IDT electrode made of a heavy metal such as, for example, a pseudo-surface acoustic wave with large propagation attenuation is made into a Love wave type surface wave without attenuation, and there is no reflector electrode or the like, and only the IDT electrode is formed. In FIG. 2B, 15 is an IDT electrode finger, and 16 is a gap (GA) for weighting rhombus.
P) is shown. Arrows (a), (b) and (c) in the figure indicate the propagation directions of the surface waves. As can be seen from FIG. 2B, the surface waves propagating through the arrows (a) and (c) are IDTs.
Although three electrode fingers pass, the surface wave propagating through the arrow (B) passes four IDT electrode fingers.

[0003]

As described above, in the above-mentioned conventional IDT electrode structure, the propagation conditions of the surface wave differ locally but depending on the location. Therefore, it is considered that the gap causes the disturbance of the surface wave propagation characteristics and deteriorates the device characteristics. FIG. 3A is a diagram showing an example of impedance characteristics of a conventional one-terminal pair resonator, and a spurious response is recognized in a portion surrounded by a circle S between the resonance point and the anti-resonance point although it is slight. Generally, when configuring a voltage controlled oscillator (VCO) using a surface acoustic wave resonator, it is required that the resonator be free of spurious. This is because even if there is an extremely small spurious response on the impedance characteristic, it may cause the oscillation frequency jump. An object of the present invention is to solve such problems and provide a surface acoustic wave resonator that suppresses spurious responses.

[0004]

The surface acoustic wave resonator of the present invention is a surface acoustic wave resonator having a weighted interdigital transducer formed on a piezoelectric substrate. Between two electrode fingers on the same terminal side next to one of the gaps provided in the electrode fingers of the electrode transducer.
It is characterized in that a short-circuit portion for short-circuiting the two electrode fingers is provided in a portion where a surface wave passing through the gap portion passes.

[0005]

The present invention will be described in detail below with reference to the drawings. As a typical example, a Love wave type surface acoustic wave resonator will be described. FIG. 1 is a plan view (A) and a partially enlarged view (B) showing an embodiment of the present invention, showing an electrode structure of a rhombic weighted Love wave type surface acoustic wave resonator. In FIG. 1A, 1 is a piezoelectric substrate, 2 is an IDT of the present invention, and 3 and 4 are connection terminals. FIG. 1B is a partially enlarged view of the portion 8 surrounded by the solid line in FIG. In FIG. 1B, 5 is I
DT electrode fingers, 6 indicates a gap (GAP), and 7 indicates a short circuit. The arrows (a), (b), and (c) indicate the propagation directions of surface waves. The short-circuit portion 7 has the same area as the gap portion 6, that is, the same width as the gap, and is provided between the electrode finger adjacent to the left and the electrode finger adjacent to the left on the same connection terminal side.
As shown in FIG. 1 (A), when weighting is applied symmetrically around the line connecting the connection terminals 3 and 4 so that the arrangement shape of the gap portion becomes a rhombus, the gap portion is centered on the center line. 6
A short-circuit portion 7 is provided in a portion between the two electrode fingers outside the area where the surface wave passing through the gap portion 6 passes. By arranging the short-circuit portion 7 as described above, the arrows (a), (b),
The propagation conditions of the surface wave propagating in (c) are totally equal in the IDT, and therefore the surface wave propagation condition of the entire IDT can be regarded as uniform. FIG. 3B is an example of a two-terminal impedance characteristic of the resonator according to the present invention,
The spurious response observed in the conventional example (A) is not observed.

[0006]

As described in detail above, by implementing the present invention, spurious responses are suppressed, so that when used in a VCO, oscillation frequency jumps do not occur and there is a great practical effect.

[Brief description of drawings]

FIG. 1 is a plan view and a partially enlarged view showing an embodiment of the present invention.

FIG. 2 is a plan view and a partially enlarged view of a conventional weighted Love wave type surface acoustic wave resonator.

FIG. 3 is an impedance characteristic example diagram of a one-terminal pair surface acoustic wave resonator according to the related art and the present invention.

[Explanation of reference numerals] 1 piezoelectric substrate 2 IDT 3, 4 terminal 5 electrode finger 6 gap 7 short-circuit 8 enlarged portion

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yuji Suzuki 2870 Wadamachi, Kofu City, Yamanashi Prefecture

Claims (1)

[Claims] 1. A surface acoustic wave resonator in which a weighted interdigital transducer is formed on a piezoelectric substrate, wherein a gap portion provided on an electrode finger of the interdigital transducer is used for weighting. A surface acoustic wave resonator, characterized in that a short-circuit portion for short-circuiting the two electrode fingers is provided at a portion between two electrode fingers on the same terminal side adjacent to one of the electrode fingers where the surface wave passing through the gap passes. .