Tom Tsao

A flexible MEMS technology and its first application to shear stress sensor skin

A new microfabrication technology that enables the integration of MEMS devices on a flexible polyimide skin has been developed. Mechanically, the flexible skin consists of many individual Si islands (necessary for silicon MEMS/electronics devices) that are connected together by a thin/thick polyimide film (typically 1-100 /spl mu/m thick). To create the islands, Si diaphragms are first formed with a desirable thickness (10-500 /spl mu/m) by Si wet etching and then patterned from the back side by reactive ion etching (RIE). As a first application, flexible shear-stress sensor skins for aerodynamics study have been fabricated. The finished skin is 3 cm long and 1 cm wide, and it consists of about 100 sensors. The skin polyimide is 17 /spl mu/m thick and the silicon islands are 75 /spl mu/m thick. These skins have been successfully taped on a semi-cylindrical (1.3 cm diameter) delta wing leading edge to perform real-time 2-D shear stress profiling.

Surface micromachined magnetic actuators

A surface micromachined micromagnetic actuator (also called a magnetic flap) as an integrated part of an active micro electromechanical fluid control system is described. The flaps are fabricated by surface micromachining technology and are capable of achieving large deflections (above 100 /spl mu/m) with magnetic forces in stationary air. Special microfabrication issues involved in fabricating magnetic flaps with large areas are discussed. Mechanical characterizations of the flaps, including the intrinsic stresses of thin film materials and frequency response, are presented. Thermal actuation is capable of producing large flap displacements and has been theoretically and experimentally studied.

A wafer-scale MEMS and analog VLSI system for active drag reduction

We describe an analog CMOS VLSI system that can process real-time signals from integrated shear stress sensors to detect regions of high shear stress along a surface in an airflow. The outputs of the CMOS circuit control the actuation of integrated micromachined flaps with the goal of reducing this high shear stress on the surface and thereby lowering the total drag. We have designed, fabricated, and tested components of this system in a wind tunnel in both laminar and turbulent flow regimes with the goal of building a wafer-scale system.