High-Performance MISiC High-Temperature Gas Sensors And Its Application

Schottky diode gas sensor with Metal-Insulator-SiC(MISiC) structure can operate at high temperature. It has the advantages of small size, low cost, short response time, simple operation circuit. Hence people focus their interests on it. It is widely used in aerospace, automobile emission monitoring, hydrogen leakage detection and other high temperature applications. It's the hotspot of extreme electronics, thus doing research on MISiC Schottky diode high temperature gas sensor is valuable both in theory and practice.Response mechanisms of MISiC SBD gas sensors are analyzed. A physical model of MISiC SBD gas sensors is established by combining SBD thermionic emission with adsorption/desorption principle of hydrogen,and considering modulation effects of barrier height and ideal factor's change with exterior conditions. The relationship between device performances and insulator thickness is investigated using the model, and an optimum thickness for high-temperature application of around 300 oC can be obtained by taking into account tradeoff between sensitivity, reliability and operation current/ resolution, which supplies scientific reference for utility.For the first time in world, technologies of growing oxynitride are used for fabrication of MISiC Schottky high-temperature gas sensor. Results show that an ultra-thin oxynitride obtained by N2O direct oxidation greatly improves properties of metal/insulator and SiC/insulator interfaces, which enhances difussion barrier and hardness of the two interfaces, and prevents the intermixing between MIS structure. When measuring the characteristics of senor, the sensor is very sensitive to the variation of hydrogen concentration and repeats well, and it even can detect low concentration hydrogen quickly.The failure mechanisms of the sensor are studied. Results show the reasons for failure mechanisms are mainly: failure of metal system, failure of catalytic metal and interdifussion under high-temperature. But the main reason is the intermixing mechanisms of the metal/insultor and SiC/insulator interfaces. Thus the failure mechanisms of MISiC Schottky gas sensors are clearly understood.To make it useful and popularized, an alarming circuit to detect H2 leakage is designed using MISiC Schottky sensors. Executing circuit board by PCB domain after designed circuit to make scientific reference for utility. From analyses on sensing and failure mechanisms, some useful results were got. The optimal design concept of the MISiC Schottky gas sensors is proposed, which supplies academic references for optimum device structures.