JP2632407B2 - Single mode two-port pair surface acoustic wave resonator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a surface acoustic wave resonator, and more particularly, to a two-terminal pair surface acoustic wave resonator of an energy trapping type surface acoustic wave resonator.

(Prior art and its problems) An energy trap type one-port surface acoustic wave resonator is usually provided on the surface of a piezoelectric substrate 1 that propagates a surface acoustic wave, as shown in FIG. One interdigital transducer 2 (Interdig) for exchanging electrical signals for surface acoustic waves
ital Transducer, hereafter abbreviated as IDT. ), A grating (grating) reflector 3 having a periodic structure is arranged on both sides. Reference numeral 4 denotes an input terminal which forms one terminal pair with the ground terminal E. The illustration of the intermediate electrode of the grating reflector 3 is omitted in this figure and the following figures.

In such a configuration, the surface acoustic wave excited by the IDT 2 is multiply reflected by the grating reflectors 3 on both sides to become a standing wave, and most of its energy is confined between the grating reflectors 3 on both sides.
At this time, the propagation direction of the surface acoustic wave (vertical direction, FIG. 1 (a)
Is indicated by an arrow. ), The vibration of the zero-order longitudinal mode, for example, in which the envelope of the standing wave has a displacement distribution as shown in FIG. 1B is excited. Although the number of electrode pairs of the IDT2 is arbitrarily large, FIG. 1 (a) shows two pairs as representatives. In FIG. 1 and subsequent drawings, the number of electrode pairs is not specified but is a representative example. Show.

The material of the piezoelectric substrate 1 is usually lithium tantalate (LiTa).
A piezoelectric single crystal substrate such as O ₃ ), lithium niobate (LiNbO ₃ ), or quartz is used. As an electrode material of the IDT 2 and the grating reflector 3, aluminum (Al), gold (Au), or the like is usually used.

Next, as shown in FIG. 2 (a), a conventional two-terminal pair surface acoustic wave resonator having two IDTs has two IDTs (2A) and (2B) on the surface acoustic wave propagation path. The two IDTs (2A) and (2B) are arranged in series, and the grating reflectors 3 are arranged on both sides of the IDTs (2A) and (2B). The input terminal 4 and the ground terminal E and the output terminal 5 and the ground terminal E 'form a two-terminal pair. The illustration of the piezoelectric substrate 1 is omitted in FIG. 2 and thereafter.

It is known that if the capacitance ratio γ of the resonator (a value proportional to the reciprocal of the difference between the resonance frequency and the anti-resonance frequency) is reduced, the pass band can be widened when a filter is configured, as shown in FIG. In a two-port resonator having a configuration, if the number of electrode pairs of IDT (2A) and (2B) is increased in order to reduce the capacitance ratio γ of the resonator, the length of the resonator becomes longer, so the propagation direction of the surface acoustic wave As shown in FIG. 2 (b), a non-harmonic first-order longitudinal mode as shown by a broken line 7 in FIG.
And there is a drawback that it becomes spurious when combined.

FIG. 4 is an actual measurement example of the input impedance of the two-terminal pair surface acoustic wave resonator having the configuration of FIG.
In B), the number of electrode pairs is 25 each, the number of grids of the reflector 3 is 300, and the piezoelectric single crystal substrate used is X-112 ゜ YLiTaO ₃ . FIG. 4a shows the basic (zero-order) vertical mode, and b shows the spurious in the first-order vertical mode.

In the two-port resonator having the configuration shown in FIG.
Since (2A) and (2B) are on the surface acoustic wave propagation path, the ID
T (2A) and IDT (2B) bind. That is, IDT (2A)
Is received by the IDT (2B), and is superimposed on the passing resonator characteristics. When a filter is constituted by such a resonator, the coupling between IDTs (2A) and IDT (2B) caused by the IDT (2B) being on the propagation path of the surface wave causes deterioration of the out-of-band attenuation.

(Object of the Invention) An object of the present invention is to provide a single-mode two-terminal pair having an electrode configuration in which the input / output IDT is not directly coupled and is not coupled to the nonharmonic first-order longitudinal mode which causes spuriousness. An object of the present invention is to provide a surface acoustic wave resonator.

(Structure and Operation of the Invention) The single-mode two-port surface acoustic wave resonator according to the present invention is provided between two lattice-like reflectors provided on a piezoelectric substrate that propagates a surface acoustic wave. Two interdigital transducers sharing the two grid-like reflectors are arranged in parallel in a direction perpendicular to the propagation direction of the surface acoustic wave, one interdigital transducer is used as an input-side transducer, and the other interdigital transducer. In the two-terminal pair surface acoustic wave resonator having a shape converter as an output-side converter, the number of electrode pairs of the two IDTs is such that both of the IDTs are coupled to only the 0th-order longitudinal mode. And the width of the two grid-like reflectors is configured to be substantially equal to the sum of the intersection widths of the two interdigital transducers. The ground electrode of the converter and the output converter is common. It is characterized in that formed.

Hereinafter, the two-port surface acoustic wave resonator according to the present invention will be described in detail with reference to the drawings.

FIG. 3 (a) shows an embodiment of the electrode configuration of a two-terminal surface acoustic wave resonator according to the present invention. 3 (b) and 3 (c) show displacement distributions, respectively. In the figure, two IDTs 2C and 2D disposed in parallel with the propagation direction of the surface acoustic wave between the two grid-like reflectors 3 have input IDs each having an independent electrode configuration.
T and an output IDT may be used, but in this embodiment, an IDT configuration is used in which the ground electrode is shared. Reference numeral 9 denotes an input terminal and reference numeral 10 denotes an output terminal. Each of the terminals 9 and 10 constitutes a two-terminal pair with the ground terminals E and E '. The piezoelectric substrate is not shown.

In the electrode configuration shown in FIG. 3A, the surface acoustic wave excited by the IDT 2C is multiple-reflected by the grating reflectors 3 on both sides to become a standing wave, and most of the energy is converted into two standing waves by the two grating reflectors 3 on both sides. And the envelope of the standing wave has a displacement distribution 6 as shown in FIG. 3 (b). However, since there is only one IDT in the propagation direction of the surface acoustic wave, even if there is an anharmonic primary longitudinal mode (7 in FIG. 2 (b)), there is no coupling, and the conventional method does not. The observed first-order longitudinal mode spurious does not occur. In addition, since there is only one IDT in the direction of propagation of the surface acoustic wave, it is apparent that the characteristic degradation due to the coupling of the input and output IDTs does not occur in the conventional method.

In the area of the grating reflector 3, since the surface acoustic wave propagation velocity is lower than that on the free surface, a surface acoustic wave waveguide is formed, and it is considered in a direction (lateral direction) perpendicular to the surface acoustic wave propagation direction. Although the horizontal mode exists independently of the vertical mode, only the 0th-order (basic) horizontal mode (11 in FIG. 3 (c)) is considered here.

FIG. 5 is an actual measurement example of the input impedance of the two-terminal pair surface acoustic wave resonator having the configuration of FIG. 3 according to the present invention.
T (2C), (2D) 25 electrode pairs each, reflector 3
The number of lattices is 300, and the piezoelectric single crystal substrate used is X-112 ゜
This is an example of Y LiTaO ₃ . As is apparent from the figure, the primary longitudinal mode spurious shown in FIG. 2 is not seen. That is, the single mode 2 having no spurious due to the configuration of FIG.
It can be seen that a terminal-pair surface acoustic wave resonator can be formed.

(Effects of the Invention) As described above in detail, the two-terminal-pair surface acoustic wave resonator according to the configuration of the present invention has two IDTs arranged in parallel in the surface acoustic wave propagation direction, and thus has a vertical It does not couple with the inharmonic first-order longitudinal mode existing in the surface wave propagation direction). That is, there is an advantage that the first-order longitudinal mode spurious does not occur.

There is only one IDT in the surface acoustic wave propagation direction.
That is, since the input and output IDTs do not exist in series on the same surface acoustic wave propagation path, the input and output
There is an advantage that spurious characteristics due to the coupling are not observed.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an electrode configuration of a conventional one-terminal pair surface acoustic wave resonator, FIG. 2 is a diagram showing an example of an electrode configuration of a conventional two-terminal pair surface acoustic wave resonator, and FIG. FIG. 4 is an example of an electrode configuration of a surface acoustic wave resonator, FIG. 4 is an example of an input impedance characteristic of a conventional two-terminal surface acoustic wave resonator, and FIG.
FIG. 4 is an example of an input impedance characteristic of a terminal-to-surface acoustic wave resonator. 1. Piezoelectric substrate, 2, 2A to 2D ... IDT (Inter-digital Tr)
ansducer, interdigital transducer), 3 ... Grating (lattice) reflector, 4 ... Input terminal, 5 ... Output terminal,
6 ... 0th-order longitudinal mode displacement distribution, 7 ... 1st-order longitudinal mode displacement distribution, 9 ... ... input terminal, 10 ... output terminal, 11 ... 0th-order lateral mode displacement distribution.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Koji Asano, Inventor 2-1-1 Shinmeidai, Hamura-cho, Nishitama-gun, Tokyo Nippon Electric Co., Ltd. Hamura Plant (72) Inventor Hiroshi Shimizu 1-22 Yagiyama Honcho, Sendai City, Miyagi Prefecture -12 (72) Inventor Yuji Suzuki 1-46, Kitsukawa, Kofu City, Yamanashi Prefecture (56) References JP-A-61-144910 (JP, A) JP-A-63-285018 (JP, A) JP-A Sho-59 -21115 (JP, A) JP-A-57-127319 (JP, A) JP-A-51-244 (JP, A)

Claims (2)

(57) [Claims] An interdigital transducer, which shares the two grid-like reflectors, is provided between two grid-like reflectors provided on a piezoelectric substrate for transmitting a surface acoustic wave. A two-terminal pair surface acoustic wave resonator which is arranged in parallel with the direction of propagation of a surface acoustic wave, and has one interdigital transducer as an input transducer and the other interdigital transducer as an output transducer. In the above, the number of electrode pairs of the two interdigital transducers is set to a logarithm such that the two interdigital transducers are coupled to only the 0th-order longitudinal mode, and the width of the two grid-like reflectors is A single-mode two-port surface acoustic wave resonator comprising substantially the same as the sum of the intersection widths of the two interdigital transducers. 2. The single-mode two-terminal pair elasticity according to claim 1, wherein a ground-side electrode of said input-side converter and said ground-side electrode of said output-side converter are formed in common. Surface wave resonator.