Silicon-micromachined flow sensors

A new generation of silicon-micromachined or micro-electro-mechanical-system (MEMS) sensors for the general purpose of microflow measurement and control is presented here. The first one is a polysilicon hot-wire anemometer made by a combined bulk and surface micromachining process. The new devices feature batch-fabricated free-standing micro polysilicon hot wires that are similar to conventional metal hot wires. Both the theoretical analysis and experimental (steady-state and dynamic) results show that MEMS hot wires have order-of-magnitude better frequency response, finer spatial resolution, and higher sensitivity over conventional hot-wire anemometers.; A novel MEMS thermal shear-stress sensor featuring vacuum-cavity insulation has been developed. The device is a polysilicon wire thermistor embedded in a silicon-nitride diaphragm which sits on top of a vacuum cavity. The vacuum cavity is to improve the thermal isolation between the polysilicon wire and substrate. To characterize the devices, both steady-state and transient heat-transfer theories have been established and used to calibrate wind-tunnel results, temperature sensitivities and frequency responses. Shear-stress sensor array chips have also been developed. Each of the shear-stress imagers has more than 100 sensors integrated on a {dollar}1 times 2.85{dollar} cm{dollar}sp2{dollar} chip. Our measurement results from a fully developed 2-D channel flow are well agreeable with previously published results. For the first time, real-time 2-D wall shear-stress images in a turbulent flow have been experimentally obtained.; A new technology for the integration of micro-sensors, micro-actuators and microelectronics (M{dollar}sp3{dollar}) on a single chip has been explored. Prototype M{dollar}sp3{dollar} chips including shear-stress sensors, magnetic actuators and CMOS circuits have been fabricated. This technology sets a base for the future development of a fully functional M{dollar}sp3{dollar} chip drag reduction.; Finally, a novel flexible MEMS skin technology fully compatible with IC process has been developed. Mechanically, the skin is made of metal leads sandwiched between polyimide layers that connect a number of silicon islands together. The skin can be applied conformably on non-planar surfaces. The first application of this technology is a flexible shear-stress sensor skin that has been successfully used for the real-time measurement of shear-stress distribution on the leading edge of a delta wing model.