Non-Toxic Liquid-Metal 2-100 GHz MEMS Switch

In this paper, the first wide-band MEMS capacitive switch using non-toxic liquid metal, Galinstan, is reported. Controlled movement of Galinstan in a micro-channel alters the impedance of a coplanar waveguide (CPW) line from 50 Omega (off-state) to an effective RF short circuit (on-state). The RF short circuit in particular is achieved when a slug of Galinstan capacitively connects the center conductor with the ground planes of the CPW line. Galinstan is reliably manipulated by surrounding it with Teflon solution. Because of Teflon, no residual liquid metal is observed when Galinstan moves. In addition, the Teflon solution has insignificant RF loss and therefore does not adversely affect the switch loss in its off-state even up to 100 GHz. The insertion loss of the switch is measured at 0.2, 0.7 and 1.3 dB at 20, 40 and 100 GHz respectively and is mainly due to the 1500 mum long transmission line. The on-state shunt capacitance is measured to be 4 pF which results in an on-state isolation of greater than 20 dB from 20 to 100 GHz.