High Temperature Smart Sensor for Downhole Logging and Monitoring

High-temperature smart sensors are desired for use in various harsh environment applications. Placing the sensing circuit close to the actual sensor would substantially reduce noise and interference problems and improve system reliability. If the circuits can operate at high temperature, this will reduce total system cost by removing the need for complicated cooling systems and will allow applications where cooling is not possible or practical. Electronic circuits based on silicon devices are generally not able to operate at high temperatures above 200oC because of excessive junction leakage currents, and even the most advanced silicon-on-insulator (SOI) devices are limited to about 300oC. In Phase I we propose to develop a high temperature smart sensor for geothermal energy applications capable of operation up to 500oC, based on 4H-SiC lateral JFET technology. The system consists of the following circuits monolithically integrated on one chip: (i) a temperature sensing circuit based on 4H-SiC p-n diodes, (ii) a voltage reference circuit, using an operational amplifier and (iii) voltage-to