Study On Low-noise CMOS Interface Circuit For Monolithic MEMS Infrared Sensor

Along with the popular application of infrared sensing technology in the military and daily life, the researchers in the infrared sensing field are trying to fabricate infrared devices with lower cost and smaller scale. The un-cooled infrared devices employing MEMS technology is under intensive attention due to its low energy consume, little weight, small scale and low cost. As one of the un-cooled infrared devices, thermopile infrared device has a simple structure comparing other MEMS devices, and the materials used in thermopile are completely compatible with the standard IC process. After integrated with peripheral circuit used to pre-process weak signals coming from the device, the thermopile infrared detectors can own a lower cost and smaller scale.The main work of this dissertation focuses on the research of monolithic infrared sensor which includes two aspects. One aspect is to design thermopile device cell based on the commercial 0.18μm CMOS process. Through carefully inspection into the IC process provided by commercial foundry HJTC, we design a feasible layout pattern to realize the structure of the thermopile device cell.In the other aspect, a low noise CMOS interface circuit is designed and implemented to pre-process the output signal of the infrared device cell. The circuit employs chopper technique which can effectively reduce the low frequency noise and amplify the weak signals. In this dissertation, we analysis the principle of the chopper technique and discuss the methods to further reduce the noise. We design a circuit system based on the chopper technique, analysis and simulate the function of circuit system, layout the whole schematics. We integrate the infrared device cell and the circuit system into the final layout pattern, and submit to the foundry HJTC to implement the fabrication of the chip. The test result proves the circuit system functions well, with 84.9dB gain, 160Hz bandwidth and 87nV/rtHz equivalent input noise. This work constructs a stable base for the further research on the large scale array of the thermopile infrared sensor.