A MEMS Floating Element Shear Stress Sensor for Hypersonic Flows

The ultimate goal of the proposed project is to develop and implement a robust, high-bandwidth, high-resolution, silicon micromachined piezoresistive floating element shear-stress sensor possessing through-wafer backside electrical contacts for themeasurement of unsteady hypersonic flow phenomena. The measurement of wall shear stress is critical to the understanding of shock-wave/boundary layer interactions which directly influence critical vehicle characteristics such as lift, drag, andpropulsion efficiency. Unfortunately the time-accurate, continuous, direct measurement of fluctuating wall shear stress is currently not possible and the realization of this capability inhibits hypersonic vehicle. To achieve our objectives, we willutilize innovative fabrication techniques and multidisciplinary optimization to realize an instrumentation-grade wall-shear stress sensor. In Phase I, we will develop a novel, lateral ion-implanted, piezoresistive floating element sensor possessing abandwidth and a spatial resolution. Once developed, this technology will be demonstrated in a bench-top experimental simulation of an unsteady hypersonic flow. In Phase II, we will employ an integrated-circuit compatible manufacturing process yielding adevice possessing electronic through-wafer backside contracts resulting in a robust flush-mounted, direct wall shear stress sensor with the electrical leads and wire bonds hidden from the flow. This sensor will then be demonstrated in a typical cold-flow hypersonic facility. The ultimate goal of the proposed project is to develop and implement a robust, high-bandwidth, high-resolution, silicon micromachined piezoresistive floating element shear-stress sensor possessing through-wafer backsideelectrical contacts for the measurement of unsteady hypersonic flow phenomena. The ability to directly measure the time-resolved magnitude and direction of mean and fluctuating wall shear stress with a spatial resolution on the order of one millimeter orless currently does not exist in any speed regime. If successful, this STTR will result in the commercial availability of instrumentation-grade, miniature sensors that will greatly extend the spatial and temporal resolution capabilities of existingdevices as well as the overall accuracy of skin friction measurement technology all speed regimes. Once an optimized sensor design and packaging scheme have been defined, strategies for volume production and packaging of the sensors will be investigatedusing commercial chip foundries. Transferring the sensor fabrication sequence from a low-volume University research environment to a high-volume commercial platform is essential for the commercialization of a high-quality, reliable device. We expect avaried set of commercial applications for the sensor technologies that we hope to prove feasible in this Phase I effort and further develop in Phase II. The natural consumers for this technology are researchers and engineers in aerospace companies andgovernment agencies involved in all aspects of thermal-fluid applications. In addition, the sensors may also be useful in fundamental fluid mechanics and biofluids research. The sensors may also find utility in the area of industrial processing asfeedback control sensors for polymer extruders.