GHz spurious mode free AIN lamb wave resonator with high figure of merit using one dimensional phononic crystal tethers

摘要

This letter reports a spurious mode free GHz aluminum nitride (AIN) lamb wave resonator (LWR) towards high figure of merit (FOM). One dimensional gourd-shape phononic crystal (PnC) tether with large phononic bandgaps is employed to reduce the acoustic energy dissipation into the substrate. The periodic PnC tethers are based on a 1 μm-thick AIN layer with 0.26 μm-thick Mo layer on top. A clean spectrum over a wide frequency range is obtained from the measurement, which indicates a wide-band suppression of spurious modes. Experimental results demonstrate that the fabricated AIN LWR has an insertion loss of 5.2 dB and a loaded quality factor (Q) of 1893 at 1.02 GHz measured in air. An impressive ratio of the resistance at parallel resonance (R_p) to the resistance at series resonance (R_s) of 49.8 dB is obtained, which is an indication of high FOM for LWR. The high R_p to R_s ratio is one of the most important parameters to design a radio frequency filter with steep roll-off.