Liquid RF MEMS Wideband Reflective and Absorptive Switches

This paper reports on the design, fabrication, and characterization of a new class of wideband liquid RF microelectromechanical-system reflective and absorptive switches. A number of different liquids are considered, including mercury, Galinstan, and ultrapure and ionic water. We first briefly review the performance of liquid–metal switches made by mercury and Galinstan. Such switches demonstrate excellent off-state insertion loss of less than 1.3 dB up to 100 GHz (the loss includes a 1500- $\mu{\hbox {m}}$-long line) and on-state isolation of better than 20 dB from 20 to 100 GHz. The main part of this paper, however, focuses on significantly transforming these designs to actually absorb and not reflect the incident power in their on-state, while at the same time maintaining their excellent off-state performance. Absorptive behavior is particularly important for high-power applications. Simpler materials such as water are proven to be very effective for wideband absorptive switches. In particular, three classes of water-based absorptive switches are discussed depending on the level of the signal coupling to water. At 10–40 GHz, the optimal design exhibits off-state insertion loss of less than 1.3 dB, on- and off-state return loss of less than 10 dB, and on-state isolation of 27.5-dB isolation at 40 GHz.