Design and Fabrication of Zero-Group-Velocity Lamb Wave Resonator onto Silicon Nitride/Aluminum Nitride Suspended Membrane

The propagation of the Lamb-like modes along an AIN/Si3N4 thin suspended membrane was simulated in order to exploit the zero group velocity (ZGV) resonant conditions, i.e. the frequencies where the mode group velocity vanishes while the phase velocity remains finite. A ZGV micro electroacoustic resonator employing only one interdigital transducer (IDT) and no reflectors was designed that is based on the propagation of the rust quasi symmetric mode qS(1) at frequency of about 1.63 GHz. The device was fabricated directly onto commercially available thin suspended Si3N4 membrane, 200 nm thick, in square silicon supporting frame (200 mu m thick). The Cr/Au interdigital transducer (IDT), with periodicity of 10 mu m, was fabricated by electron beam lithography (EBL) directly onto the Si3N4 membrane; then the piezoelectric AIN layer was grown onto the membrane at room temperature by rf reactive magnetron sputtering technique. The technological feasibility of the ZGV resonator on commercial Si3N4 suspended membrane is demonstrated and preliminary experimental results are shown.