An Ultra Wide Range Mems Variable Capacitor with a Liquid Metal

This paper describes a novel variable capacitor with a wide tuning range by utilizing thermal expansion characteristics of a liquid metal. The liquid metal moves through microfluidic channel and interconnects multiple capacitors in parallel. It has many advantages over the other types of MEMS variable capacitors, which generally have many limiting factors in the tuning range. The gap-tuned capacitors by vertical electrostatic actuation have a very narrow tuning range and it is significantly affected by pull-in effect. Another design by separating the driving electrodes and the parallel plates has been implemented but still the tuning range is not more than 3 times. Similarly, piezoelectrically tuned capacitors have become popular, but the tuning of the capacitance is not linear with respect to the actuation voltage. The other interesting variable capacitor is the area-tuned capacitor by a lateral electrostatic actuation of comb-drive structures but capacitance variation is not linear and also the range is pretty much limited (< 3 times). Our novel device is based on the thermal characteristics of very linear expansion of a liquid metal and attempts to overcome all the above difficulties.