Interdigitated-comb piezoelectric phononic crystals for innovative SAW devices

In this paper, piezoelectric phononic crystals made up of interdigitated combs in floating potential condition are studied. Calculation of the dispersion curves shows that, in addition to Bragg bandgaps due to the presence of periodic electrodes, supplementary bandgaps are present corresponding to electrical resonance/antiresonance of the comb pairs. Calculation of the reflection coefficient of finite-sized mirrors reveals the presence of high amplitude reflection coefficient lobes near these bandgap frequencies. The electrical response of single port resonators using these interdigitated comb mirrors fabricated with Al metallization on LiTaO3 POI substrate is contrasted with that of a resonator with classical mirrors, providing experimental verification of this mechanism for bandgap opening. Possible applications for SAW device design are finally discussed.