Reflective Strategy Based on Tether-Integrated Phononic Crystals for 10 MHz MEMS Resonator

As an emerging technology, thin-film piezoelectric-on-silicon micro-electro-mechanical systems (TPoS MEMS) resonators have attracted much attention. However, in order to promote it forward to practical applications, such as wireless communications and autonomous sensor networks, further improvements are needed in particular in the enhancement of quality factor ($Q$). In this paper, the traditional approaches based on reflector structure and phononic crystals (PnC) structure was comprehensively studied by both experiments and simulations. Therefore, a reflective strategy based on tether-integrated PnC was proposed to reduce the anchor loss and then boosted its $Q$. Moreover, two kinds of cross-shaped PnC structure (i.e., have complete bandgaps covering the resonant frequency) were proposed to obtain considerable $Q$, while keeping extremely small lattice constant at low resonant frequency of 10 MHz. More specifically, the lattice constant of proposed 1D ($50\mu \text{m}$) and 2D ($100~\mu $ m) PnC structure is smaller than the relevant acoustic wavelength ($850\mu $ m) by 17 and 8.5 times, respectively. And the anchor loss ($Q _{\mathbf {anc}}$) of this novel design (i.e., ${P2D}$ with $Q _{\mathbf {anc}}$ of 538,000) achieved a maximum 53-fold enhancement compared with the pristine one (i.e., $N$ with $Q _{\mathbf {anc}}$ of 10,100).