Fabrication of low-resonant-frequency inertial MEMS using through-silicon DRIE applied to silicon-on-glass

This paper reports on a fabrication process suitable for ultra-low resonant frequency inertial MEMS sensors. The low resonant frequency is achieved by electrically tunable springs and a heavy mass formed by through-silicon deep reactive-ion etching (DRIE) applied to a silicon-on-glass. A thermal issue of through-silicon DRIE (TSD) stemming from the low-resonant-frequency structure is circumvented by two methods: introducing cooling time between the DRIE steps, and adopting a metal hard mask. A blade dicing method suited for this process is also presented. To monitor the verticality of TSD, a non-destructive taper detection method that utilizes a capacitance-voltage (CV) curve is proposed and verified.