Microactuation based on thermally-driven phase-change

The authors describe a microactuator based on thermally induced liquid-vapor phase-change in a partially filled closed cavity. A test structure for studying such systems has been designed and fabricated. The cavity is 900 mu m*900 mu m*300 mu m in size with a 600 mu m*800 mu m heater covering the floor of the cavity and elevated approximately 10 mu m above it. These heaters have open diamond-shaped unit cells defined by 12 mu m-wide 3 mu m-thick bulk silicon beams and provide an overall electrical resistance of 3-10 Omega . The thermal resistance is typically 4-6 degrees C/mW so that the heater temperature rises approximately 22 degrees C for input current levels of 25 mA. Using Freon-11 as the cavity fluid with partial filling, very modest drive levels are thus able to sustain a 1-atm pressure rise within the cavity. Overdriving the heaters at 100 mW results in a simulated pressure rise of 1 atm in 40 ms, showing that operation can be rapid as well.<>