Impact of Piston Design on Lateral Leakage Suppression in I.H.P. SAW Resonator

Although the anti-resonance Q (Qa) of SAW resonators has been enhanced dramatically in recent years by the introduction of I.H.P. configuration, the resonance Q (Qr) was scarcely improved because the ohmic resistance of IDT electrodes limits achievable Qr. One possible way to resolve this problem is reducing the IDT aperture. However, it also causes the Qa reduction in general. Recently, it was shown that the in-plane SAW diffraction gives a significant impact to Qa, and becomes serious when the aperture length is small. This paper discusses the loss mechanism when the in-plane diffraction is suppressed and shows the piston design affects the Bode Q in the case. The possibility to reduce the aperture length while maintaining the Qa is demonstrated.