RF-MEMS switching devices using vertical comb-drive actuation in the CMOS process

Abstract

Radio frequency micro-electro-mechanical system (RF-MEMS) switching devices using vertical comb-drive actuation toward low-voltage actuation, fast response are presented in this paper. The switching devices, which comprise comb-drive electrodes, are actuated entirely by the electrostatic forces applied not only for the down-state but also for the up-state. The cost-effective MEMS process compatible with the complementary metal oxide semiconductor (CMOS) process is presented in this paper as well. The fabrication process is composed by adapting the CMOS 0.18 µm back end of line (BEOL) process on 200 mm wafers. The MEMS process in the CMOS process enables the realization of passive devices integrated with active devices, which is effective for size and cost reduction. Two metal interconnection layers in the BEOL process are used for the MEMS process. Interconnection aluminum and inter-layer dielectric tetraethoxysilane (TEOS) are used as MEMS structural material and sacrificial material, respectively. The chemical mechanical polishing (CMP) process is implemented to planarize the sacrificial material surface. The structures were fabricated using a simple low-cost two-mask process. The characteristics of switching capacitors, C-V, RF performance, switching speed and continuous drive cycles are measured on the fabricated devices. The capacitance ratio for the down-state/up-state is Cdown/Cup = 5.4. The characteristics of switching speed response/actuation voltage in the down-state and up-state are 4.5 µs/5 V and 8.0 µs/5 V, respectively. The switching speed is stable up to 107 cycles in spite of the fact that the unipolar voltage speed is stable up to 107 cycles.