Love‐wave‐type/Rayleigh‐wave‐type SAW resonators with thick Al‐grating structure

Abstract

SUMMARYA Love-wave SAW propagating on a thick Al grating on a LiNbO 3 piezoelectric substrate exhibits a resonant characteristic with an extremely small capacitance ratio γ (= 3.0) while it elastically couples with Rayleigh waves in a complex manner. In the application to a resonator, the Rayleigh wave becomes spurious and must be suppressed sufficiently. With a view to development of a broadband SAW resonator for a VCO, the propagation/reflection characteristics of this Love-wave/Rayleigh-wave configuration are analyzed. The following results are found by simulation and experiments. (1) Both the Love wave and Rayleigh wave have extremely wide reflection bandwidths. (2) Two types of spurious Rayleigh wave appear in the resonant characteristics. (3) The stopband of the Rayleigh wave is superior in reflection characteristic to the Love wave. It is also demonstrated experimentally that a broadband SAW-VCO can be realized if the VCO oscillation frequency is chosen within the Rayleigh wave stopband after the Al film thickness is optimized.

Ultra‐wideband SAW resonator composed of grooved Cu electrodes and its application to tunable filters

“…In the FEM, the frequencies at the upper and lower edge stopband edges are obtained for a short grating and an open grating. Among these, one of the frequencies in the short grating and one of the other frequencies for the open grating agree, while the remaining frequency for the short grating is equivalent to the resonance (fr) and the remaining frequency for the open grating is equivalent to the antiresonance (fa) [15]. Figures 2 to 5 show the electromechanical coupling factor for the electrodes and the reflection coefficient [13][14][15] at one finger in the shorted electrode.…”

“…Among these, one of the frequencies in the short grating and one of the other frequencies for the open grating agree, while the remaining frequency for the short grating is equivalent to the resonance (fr) and the remaining frequency for the open grating is equivalent to the antiresonance (fa) [15]. Figures 2 to 5 show the electromechanical coupling factor for the electrodes and the reflection coefficient [13][14][15] at one finger in the shorted electrode. When the acoustic velocities equivalent to the resonance and antiresonance described above are both slower than the slow bulk shear waves, then a Love wave with no leaky component is obtained.…”

“…We fabricated a SAW resonator using a Cu electrode and confirmed that the configuration with an embedded electrode yielded greater bandwidth. Figures 2 to 5 show the electromechanical coupling factor for the electrodes and the reflection coefficient [13][14][15] at one finger in the shorted electrode. In the BPF type, a 6.8% variable range was obtained in a tunable filter formed with a fixed capacity on a substrate instead of a variable capacity.…”