MEMS-based series and shunt variable capacitors for microwave and millimeter-wave frequencies

This article describes design and modeling of MEMS-based variable capacitors with rf performance acceptable for microwave and millimeter-wave applications. Appropriately designed thermal actuators are used to move the MEMS capacitor plate vertically to change the air gap between the MEMS plate and the signal line of a coplanar waveguide (CPW). Both series- and shunt-mounted capacitors have been demonstrated. Effect of actuator design on rf performance is investigated by electromagnetic simulation. Experimental results show an air gap change resulting in a capacitance variation with a ratio of 2.7:1. For the shunt-mounted capacitor, the capacitance showed no self-resonance and the equivalent resistance is less than 0.5 Ohm in the frequency range up to 40 GHz. The MEMS-based variable capacitors are described with an emphasis on rf design and characterization. in particular, the effects of actuator design on rf performance are discussed in details. (C) 2001 Published by Elsevier Science B.V.