Phase Noise Analysis of MEMS-Based Phase Shifters

The effect of Brownian noise on Micro-Electro-Mechanical (MEMS)-based circuits has been calculated for MEMS-based circuits (phase shifters, delay circuits). The calculations are done for capacitive shunt MEMS switches and metal-to-metal contact series MEMS switches. The phase noise due to Brownian motion is negligible for MEMS switches with k ¿ 10 N/m, g0 > 2 ¿m, Q > 0.5, and f0 ¿ 50 kHz. It is also found that metal-to-metal contact series switches result in much less phase noise than standard capacitive shunt switches. The phase noise increases rapidly for low spring-constant bridges (k =0.2-4 N/m), low-height bridges, and for bridges with a large mechanical damping (Q < 0.3). Also, varactor-based designs result in 30-40 dB more phase noise than switch-based circuits. The paper proves that microwave passive circuits built using MEMS switches (with a proper mechanical design) can be used in most commercial and military applications without any phase noise penalty.