Research Of The Structure And Preparation Technology Of A MEMS Capacitive Infared Detector For Gas Detection

The gas analysis is not only used in the traditional industry like mine safety, chemical process control and public safety, pollution monitoring, agricultural facilities, etc but also in health care, even in biological science, microelectronics, new materials and new technology more and more. We introduce several gas detecting methods which are put into practical application currently and their respective advantages and disadvantages, and then come up with great significance of infrared gas detecting methodsSummarizing the predecessors' research achievements, this paper proposes a kind of MEMS capacitive infrared detector, based on infrared absorption of gas, for gas detecting. The parallel plate capacitor with a double-capacitance structure can effectively restrains the effect of temperature and other environmental factors on the stability of the infrared detector. After confirming the basic structure, the paper gives detailed introduction on its preparation material. Getting the heat distribution on cavity wall and the thermal stress distribution on elastic thin film through ANSYS simulation, and combining with the process realizing, we determine the better structure and size of the cavity, thickness of the Elastic film and plate spacing of the parallel plate capacitor. MEMS process technology is a key factor for micro-systems'implementation, in this paper, we make a comprehensive research on the process involved in the preparation of infrared detector, then combine various process technology to achieve optimal expected detection index.We select the half bridge detecting circuit with an operational amplifier toward the detector's tiny capacitance output. This can ensure reference capacitor effectively restrain outside interference factors'effect on the output signal, and also change the nonlinear relationship between the capacitance with plate spacing into approximate linear relationship between voltage output and infrared light intensity. According to theoretical derivation results, we work out the characteristic curve of the infrared detecting system, its sensitivity and linear detection range are respectively: 0.867 V/cd and 0 -0.1cd.