| Shear stress at the solid-fluid interface is a frequently studied parameter in fluid dynamics because of its relevance to many engineering applications, such as those in aerodynamic and hydrodynamic design. Shear stress measurements are also critical in biomedical and environmental science research. For example, shear stress data, lead to improved understanding of fluid flow physics in cardiovascular systems and coral reef ecologies.;The core element of this work is the design, fabrication, characterization, and testing of piezoresistive floating-element shear stress sensors. Conventional and oblique-angle ion-implantation techniques were used to form piezoresistors on the top and sidewall surfaces of the tethers. Hydrogen anneal technology was used to smooth sidewall scallops commonly seen in the Deep Reactive Ion Etching process and to reduce the noise in sidewall piezoresistors by almost an order of magnitude. A microfabricated piezoresistive cantilever was used to characterize the in-plane sensitivity, while Laser Doppler Vibrometry was used to characterize its out-of-plane sensitivity.;The SiO2/Si3N4/SiO2 triplex layer and Parylene C were used as passivation schemes in two underwater experiments. The first experiment used a cylindrical water tank sitting on a rotating table to produce solid body rotation. The second experiment used a gravity-driven water flume to create a uniform, fully-developed flow over the sensor. Polymer flip-chip flexible interconnects were fabricated and used for the packaging of the sensor in the gravity-driven water flume experiment.;Finally, a novel sidewall epitaxial piezoresistor fabrication process using selective deposition and early findings on electromechanical characteristics of cantilevers fabricated using this technique were demonstrated for in-plane force sensing applications. |
