Frame structure for thin-film piezoelectric-on-silicon resonator to greatly enhance quality factor and suppress spurious modes

Thin-film piezoelectric-on-silicon (TPoS) bulk acoustic wave resonator provides an attractive vision of system-on-chip integrated circuits by micro/nano-engineering the timing reference. However, its quality factor (Q) at high frequency is a great challenge due to the mechanical loss. Herein, a novel suspended frame structure on tethers was proposed to significantly enhance the Q and suppress spurious modes of TPoS resonator working in the 30.4 MHz fundamental mode. Compared with the pristine one, the measured Q of fabricated resonator with frame structure showed a maximum 136-fold enhancement. The systematical investigation by both finite-element-analysis (FEA) simulation and experimental comparison revealed that the existing of frame structure effectively decreases the effective coupling coefficient (k2eff) of resonator and further results in the suppression of spurious modes and the enhancement of Q. As the width of frame structure increases, the k2eff maintains a consistent value of 0.15% while the anchor loss significantly reduced, which results in the reduction of insertion loss (IL) and the enhancement of Q.