MEMS based SnO2 gas sensor with sol gel synthesized mesoporous nanocrystalline (<10 nm) semiconductor thin (100~150 nm) film has been recently developed. The SnO2 nano film is fabricated with the combination of polymeric sol gel chemistry with block copolymers used for structure directing agents. The novel hydrogen sensor has a fast response time (1s) and quick recovery time (3s), as well as good sensitivity (about 90%), comparing to other hydrogen sensors developed. The improved capabilities are credited to the large surface to volume ratio of gas sensing thin film with nano sized porous surface topology, which can greatly increase the sensitivity even at relatively low working temperature. The gas sensing film is deposited onto a thin dielectric membrane of low thermal conductivity, which provides good thermal isolation between substrate and the gas-sensitive heated area on the membrane. In this way the power consumption can be kept very low. Since the fabrication process is completely compatible with IC industry, it makes mass production possible and greatly reduces the cost. The working temperature of the new sensor can be reduced as low as 100°C. The low working temperature posse advantages such as lower power consumption, lower thermal induced signal shift as well as safe detection in certain environments where temperature is strictly limited.
Robust compact hydraulic actuators are extremely needed in space industry where payload is critical. Microvalves are key component for compact hydraulic actuators. Robust microvalves with large load bearing ability, large flow rate, and high operational frequency are objectives of this research. A FEM analytical approach was used to optimize the valve design. The microvalves were fabricated by novel microfabrication process and scaling laws. Electroformed nickel on silicon substrate was used to make the valve flap and deep RIE etching was adopted to make the valve channels while the metallic valve flap as the etching stop. Test results shown that the flow rate is proportional to the pressure applied. The flow rate is larger than 10 cc/sec at pressure or 40 psi. These microvalves can be used to solve engineering problems where both load bearing and flow rate are major concerns.