CMOS-MEMS Variable Capacitors Using Electrothermal Actuation

Microelectromechanical-systems variable capacitors which are monolithically integrated with CMOS using a post-CMOS fabrication process are presented. The variable capacitors use electrothermal actuation for lateral gap tuning. A mechanical latch is included to maintain the capacitance at different values without expending power. Measured tuning ratios up to 6.9 : 1 are reported with a Q of 95 at 1 GHz corresponding to the maximum capacitance and an electrical self-resonant frequency of 11 GHz. The capacitors can be reconfigured in 30 ms using no more than 3 V and 15 mW for actuation. The latched capacitance values are repeatable to within 1% of their nominal value and remain stable for ambient temperatures up to 65 ^C. Reliability testing shows that the capacitor is capable of millions of cycles and that the latched capacitance values remain stable after applying accelerations up to 40 g.