This Small Business Innovation Research (SBIR) Phase I project will address bulk micromachining of single crystal silicon carbide and III-V nitride semiconductors to develop miniaturized fluid density and viscosity sensors based on acoustic wave (AW) principles. Phase I will develop sensors capable of precisely measuring fluid viscosity and density over wide limits under harsh operating conditions: high pressure, high temperature, corrosive, or abrasive. The harsh environments require fabrication of microelectromechanical systems (MEMS) for fluid viscosity-density sensors from silicon carbide (SiC) and gallium-aluminum nitride (GaN-AlN) compounds, which have high melting temperatures (1700-3000 degrees Centigrade) and favorable chemical and mechanical properties. Phase I will test the feasibility of the micromachined SiC-AlN fluid viscosity-density sensors by fabricating an unpackaged pre-prototype device from these materials and demonstrate the measurement of viscosity and density in a variety of fluids at various temperatures and pressures.<br/><br/>Harsh-environment MEMS fluid viscosity and density sensors have commercial applications in boreholes for oil exploration and production, monitoring of engine fluids in automobiles, aerospace and military vehicles, and monitoring chemical synthesis and production processes. These devices are expected to increase oil-well production at reduced cost, promote more efficient use of engine fluids resulting from direct and continuous feedback of fluid characteristics, and enable real-time in situ monitoring of chemical processes.