Thermally driven phase-change microactuation

This paper describes a microactuation scheme based on thermally driven liquid-vapor phase-change in a partially filled sealed cavity. A test structure for studying this system has been designed and fabricated. The cavity is 900 μm by 900 μm by 300 μm in size with a thin, 600 μm by 800 μm grid-shaped heater located on the floor of the cavity and elevated approximately 8 μm above it. The heater is composed of open diamond-shaped unit cells defined by 12-μm-wide, 3-μm-thick bulk-silicon beams, giving an overall electrical heater resistance of 3-10 Ω. Using methanol as the cavity fluid with partial filling, drive levels of 10 mW sustain a 1.2-Atm pressure rise within the cavity. Real-time measurements demonstrate a pressure response time on the order of 100 ms for an input power of 100 mW. Simulated pressure response calculations indicate the potential for an optimized response time on the order of 40 ms at this power level