Piezoresistive characteristics of silicon carbide for integrated sensor applications

Successful ubiquitous deployment of advanced reactors will depend to a large extent on the development of high-performance materials and sensors. Recently, there has been increasing interest in advanced reactors operating at very high temperatures (greater than 700 °C) and using molten salts as the primary coolant. In such reactor systems, temperature and pressure measurements are conducted using standard legacy thermocouples and pressure measurement technologies, both of which suffer from resolution issues, inaccuracies, and drift under harsh operating temperature and radiation conditions. We report on the structural, electrical, and mechanical characteristics of SiC materials and devices for the development of an integrated monolithic sensor unit capable of simultaneously monitoring temperature, pressure and flow in molten salt reactors, while at the same time exhibiting significant improvements in resolution, accuracy and signal-to-noise ratio. Wide bandgap and chemical inertness of SiC make it suitable for harsh environment sensor applications. We report on the development of a SiC pressure sensor exploiting its piezoresistive properties. Attempts have been made to fabricate thermally stable pressure sensor through doping induced high gauge factor. Both n-type and p-type SiC wafers, implanted and in-situ doped, have been investigated in the present study to analyze the impact of dopant type and concentration on the piezoresistive characteristics. The microstructure and composition of SiC samples have been analyzed by AFM, XRD, SIMS, and RBS techniques. The electrical conductivity of the SiC samples has been measured by 4-point probe technique. The mechanical measurements are being conducted on SiC beams with photolithographically defined surface piezoresistors. Temperature dependent electrical properties of the doped SiC sensors are also being investigated to develop high performance sensors that can operate at temperatures beyond the limits of conventional silicon CMOS materials and devices.