Enhanced anchor quality factor of an aluminium nitride-on-silicon MEMS resonator using support tethers based on compound leaf-shaped one dimensional phononic crystal

Abstract

Energy dissipation through support structures is one of the dominant loss mechanisms in MEMS resonators, which results in a very low quality (Q) factor. This paper aims to propose a one-dimensional phononic crystal (PnC) structure, namely a compound leaf-shaped phononic crystal (PnC) strip (TYPE_PROP), as anchor tethers to boost the anchor quality factor (\(Q_{anchor}\)) of a thin-film aluminium nitride (AlN)-on-silicon (Si) MEMS resonator. Thus, its Q can achieve a superior value. The operating frequency and mode of the resonator are 123.49 MHz and a length extensional (LE) mode, respectively. This frequency falls into the band gap frequency range of 52 MHz of the TYPE_PROP. The \(Q_{anchor}\) of the resonator with unit cell number variation of the TYPE_PROP tether is studied. From these investigations, the effectiveness of the tether in reducing/eliminating the anchor energy loss is evaluated. Furthermore, this \(Q_{anchor}\) is also compared to the same resonator structure with two conventional tether types. Additionally, the variation of the band gaps’ properties versus the dimensional parameters of the TYPE_PROP are also evaluated. The COMSOL Multiphysics platform based numerical results demonstrate that the \(Q_{anchor}\) of the resonator with the TYPE_PROP based tethers achieves superior values compared to its counterparts. Specifically, this value is about 5.42 \(\times\) \(10^{12}\) and 23.74 times higher than that of the TYPE_CON1 and TYPE_CON2, respectively. The \(Q_{anchor}\) improvement of the LE mode MEMS resonator using the TYPE_PROP achieves higher values than that using two conventional tether configurations.