Continuously tunable RF-MEMS varactor for high power applications

A high power continuously tunable RF-MEMS capacitor (varactor) for frequencies from DC−4.0 GHz is presented. The device is specified for 0.8-1.6 pF analog tuning range and provides a Q factor of ≫100 for frequencies below 2.0 GHz. Using silicon bulk technology and wafer bonding techniques, RF and electrostatic actuation electrodes are arranged vertically. It enables controlled counteracting the attractive electrostatic forces generated by high RF signal amplitudes (self actuation). Using a time domain reflectometer based measurement setup and a resonating test circuit, stability against CW signals of up to 55 V rms has been shown. Due to the highly damped mechanical response, the capacitance setup is intrinsically insensitive to RF bursts (tp=20 μs) of more than 120 V rms.