Pneumatic RF MEMS switch using a liquid metal droplet

We introduce a new design for radio frequency (RF) microelectromechanical systems (MEMS) switch that uses a liquid metal (LM) droplet as a switching component. The switch uses a polymer membrane atop the droplet as a pressure transducer. Initially, a signal passes through a coplanar waveguide (CPW) line (i.e. the switch is on). Pneumatic pressure on the membrane pushes the droplet, thus reducing the gap between the bottom surface of the LM droplet and CPW line; when the gap becomes less than a critical distance, the signal is blocked (i.e. the switch is off). This switch is more stable and has better isolation than do existing RF MEMS switches that use LM droplets. We used a commercial simulation tool (CST Microwave Studio®) to confirm the feasibility of the concept, then fabricated a prototype device that has the same insertion loss as the reference configuration (i.e. a CPW line only). Applying ∼35 kPa pressure to the flexible membrane resulted in switching performances with ∼50 dB isolation at 3 GHz and when the pressure is removed, the switch insertion loss was measured ∼1.5 dB.