Anchor quality factor improvement of a piezoelectrically-excited MEMS resonator using window-like phononic crystal strip

Abstract

Owning a superior quality factor (Q) helps contribute to the advantages of microelectromechanical systems (MEMS) resonators due to its impact on the performance of MEMS technology-based oscillators and filters in IoTs and radio frequency applications. Anchor quality factor (\(Q_{\textrm{anchor}}\)), which measures the anchor energy loss from the MEMS resonators into their substrate, is one of the main parameters in determining Q. In this paper, a window-like phononic crystal (PnC) strip, namely W-PnC, is proposed to act as a barrier of elastic wave propagation in the support tethers of an Aluminium Nitride (ALN)-on-Silicon (Si) resonator. As a result, the resonator \(Q_{\textrm{anchor}}\) is boosted highly. This W-PnC generates a bandgap (BG) with a width of 24.11 MHz. which covers the 152.5 MHz resonant frequency of the resonator. Three traditional support structures, including phononic crystal without hole (WH-PnC), phononic crystal with circle stub (C-PnC), and quarter wavelength (L-tether), are the counterparts of the W-PnC in the comparison of the \(Q_{\textrm{anchor}}\) improvement. By changing the dimensional parameters of the W-PnC, the variation of the BG formation in its band structures is evaluated to provide a platform for the designers in choosing the optimal BGs. The numerical results show that \(Q_{\textrm{anchor}}\) of the resonator with the W-PnC is superior to its counterparts. Specifically, the \(Q_{\textrm{anchor}}\) of the resonator investigated with the two unit cell W-PnC increases 510.90%, 1771.70%, and 1048.51% over the WH-PnC, C-PnC, and L-tether, respectively. The W-PnC demonstrates its high effectiveness over other counterparts in reducing/eliminating the anchor dissipation energy source of the resonator. In addition, the BG properties of the W-PnC, such as gap width and gap location, depend on its dimensional parameters. The finite element analysis based numerical simulation method in this work is performed in COMSOL Multiphysics. The MATLAB scripts then solve the posting process of these simulations.