A dielectric liquid contact thermal switch with electrowetting actuation

Abstract

We present the design, fabrication and characterization of a new kind of MEMS thermal switch based on electrowetting actuation of a dielectric liquid contact. The thermal switch consists of a thin layer (30–120 µm thick) of a dielectric liquid, such as glycerin or water, squeezed between two silicon dies. The gas pressure in the gap can be varied from ambient down to 0.6 T. The switch operates by changing the conductive path between the two silicon dies by moving the thin layer of dielectric liquid using electrowetting. The result is a bi-stable thermal switch that can change between a low thermal resistance state and a high thermal resistance state. Electrowetting measurements indicate switching time on the order of 2–40 s with switching time increasing as gap width decreases. The power required to switch states is less than 2 mW. Heat transfer measurements indicate thermal resistance ratios of up to ROFF/RON = 14, with the highest thermal resistance ratios found for the smallest gap (30 µm) and the lowest pressure (0.6 T).