Improvement of Deep Reactive Ion Etching Process For Motional Resistance Reduction of Capacitively Transduced Vibrating Resonators

Motional resistance is one of the most important performance metrics for high quality factor, low power, and complementary metal-oxide semiconductor (CMOS)-compatible capacitively transduced vibrating micromechanical resonators. The motional resistance is primarily set by the electrode-to-resonator air gap that can be formed by deep reactive ion etching (DRIE) process. Although the state-of-the-art DRIE technologies can achieve a narrow capacitive air gap down to 1 μm or less, the effective gap tends to be larger than designed values due to the sidewall roughness known as scalloping. Systematic modifications of all key process parameters are presented in this article for lowering the sidewall roughness to result in an up to 2× reduction of the effective capacitive transducer gap, which could lead to an up to 16× decrease of the effective motional resistance.