Amorphous-Carbon/Si Heterojunction device for Room Temperature NH3 Sensing and Development of Readout Circuit for Chemiresistive Sensor

Classical metal oxide gas sensors are used to be operated at relatively high temperatures to achieve good sensitivity. So there is a strong need to develop a gas sensing platform that provides either low temperature or room temperature sensing, so as to reduce the power consumption. Keeping this in mind, in this work, we have proposed and fabricated an amorphous-Carbon/Silicon (a-C/Si) heterojunction based room temperature ammonia gas sensor. We have optimized the fabrication process flow for obtaining a stable a-C thin film on Si substrate with strong adhesion. Here, to develop the a-C film, we have used pyrolysis of negative photoresist material SU8, which also provides us with the added benefit of photo-patternability. One of the desired outcomes of the proposed work is to provide a reduced response and recovery time. Also, we have targeted to achieve a low limit of detection with high selectivity. Additionally, we have developed a readout circuit for chemiresistive sensors, where change in device resistance is used as a transduction principle for targeted analyte detection. The circuit is designed to meet the specification of the sensor, where the desired detection range extended up to a few hundred Mega ohms. The requirements of the system have been studied and implemented using Cadence. The prototype of the circuit has been designed and tested