Mechanistic optimization of RF-MEMS capacitive switches: low-roughness material stacks for superior mm-wave reliability

Official URL: https://dx.doi.org/10.1109/ICM66518.2025.11321326

Surface roughness is the dominant factor degrading the mechanical reliability and dictating the ultimate electromagnetic (EM) performance of RF-MEMS capacitive switches. This study pioneers a mechanistic optimization approach by systematically defining and evaluating low-roughness material stacks to achieve superior device characteristics. We investigated Al, Au, Cu, and Ag for the coplanar waveguide (CPW), combined with Al2O3, Si3N4, and SiO2 as dielectric layers, fabricating and characterizing twelve critical configurations. Through rigorous AFM and SEM analysis, correlated with MATLAB-based EM modeling, we quantified the direct impact of material configuration on device performance. Specifically, the Au/Al2O3 stack demonstrated a superior normalized up-state capacitance of 1.17 and an insertion loss of 1.73. The normalized down-state capacitance and normalized isolation for Al/SiO2 are 15.31% and 0.73 respectively, at an RMS roughness of 25 nm when the actuation voltage is 20 V. In the optimized case, the preferred configuration yields a 27% reduction in isolation loss and a 73% increase in insertion loss compared to non-optimized benchmarks. We propose specific material configurations, including Au/Al2O3 and Al/SiO2, as decisive solutions for RF-MEMS fabrication, delivering enhanced reliability and state-of-the-art mm-wave performance essential for next-generation wireless systems.