Study of the LT/Quartz Bonded SAW Substrate for high performance filter solutions

For expanding into various newly allocated frequency bands, high K2, high Q filter solutions are strongly demanded for RF filter modules. Recently, SA W-type devices with bonded wafer structures have been widely studied for achieving high Q, high K2 and excellent TCF. For example, 42YX-LiTaO3 bonded onto Quartz has been studied as a candidate combination to provide high performance filter solutions with high Q, excellent TCF, and a spurious-free clean response. This paper proposes 25YX-LiTaO3 bonded on 70Y90X-Quartz to give high K2, high Q, and good TCF while suppressing spurious transverse modes, without any other special treatment to support piston mode operation. A parametric sweep study for this feature was conducted by piezoelectric simulation. Experimental filters and resonators were fabricated on 25YX-LiTaO3 bonded on 70Y90X-Quartz, and the resulting performance and TCF were evaluated. This paper proposes 25YX-LiTaO3 bonded on 70Y90X-Quartz as a candidate structure for high performance filter solutions. Ladder and DMS-type filter prototypes are demonstrated with excellent TCF performance and clean pass bands free of transverse modes.