First shear horizontal mode plate wave in LiNbO3 showing 20 km/s phase velocity

Currently, cognitive radio using a white space of digital TV (DTV) channels is receiving a lot of attention. One of the key devices of a cognitive radio handset is a tunable filter capable of adjusting frequency and bandwidth (BW) throughout DTV band. The authors developed ultra-wideband resonators in a DTV band and ultra-wideband filters fully covering all DTV channels using 0th shear horizontal mode plate wave (SH₀) in a (0°, 120°, 0°) LiNbO₃ plate. However, they are fabricated on a self-suspended ultra-thin LiNbO₃ plate of only 0.5-0.6 μm in thickness, which is mechanically fragile and difficult to fabricate at high yield. A much higher phase velocity than that of SH₀ is required to make the plate practically thicker. The objective of this study is to explore a different mode of plate wave showing much higher phase velocity and wide BW. By FEM simulation, it is clarified that a first SH mode (SH₁) plate wave propagating in two kinds of new proposed structures, which are different from suitable SH₀ mode structures for wide BW, has higher velocity than 20,000 m/s and wide BW of 24%.