Piston-like design of surface acoustic wave resonators for suppression of longitudinal mode resonances

Abstract This paper discusses the applicability of the piston mode design to the suppression of longitudinal mode (LM) resonances in surface acoustic wave (SAW) resonators. It is shown that LMs below the main mode (MM) resonance can be suppressed well by modulating the finger periodicities of reflectors and the interdigital transducer (IDT) properly. Then, modulating the metallization ratio (MR) is also discussed. It is shown that setting larger MR to the reflectors than the IDT enables us to extend the separation between the MM antiresonance and the upper stopband edge of the reflectors. Finally, the impact of tapering the reflector's outer edges is discussed. It is shown that the LMs above the reflector stopband can be also suppressed well in addition to those below the reflector stopband without sacrificing the other resonator performances.