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Integrated CMOS gas sensors

TitleIntegrated CMOS gas sensors
Publication TypeConference Paper
Year of Publication2009
AuthorsBhat, N, Jayaraman, B, Pratap, R, Bagga, S, Mohan, S
Conference NameElectron Devices and Semiconductor Technology, 2009. IEDST '09. 2nd International Workshop on
Date PublishedJune
KeywordsCircuits, CMOS Gas Sensors, CMOS integrated circuits, CMOS platform, CMOS technology, Control systems, convertors, design criteria, digital converter, dynamic response, Electric resistance, electrical equivalent model, Gas detectors, gas sensors, heater current, integrated CMOS gas sensors, laser Doppler vibrometer measurement, low power gas sensor system, mechanical poles, micromachined polysilicon microheater, Polysilicon microheater, power MOSFET, resistance readout circuit, Semiconductor device modeling, SnO2, static response, subranging technique, subthreshold operatin, subthreshold operation, Subthreshold read-out, Temperature control, Temperature controller, temperature controller circuit, temperature sensor, Temperature sensors, temperature uniformity, thermal poles, time period conversion, transducer film, Transducers

We present a low power gas sensor system on CMOS platform consisting of micromachined polysilicon microheater, temperature controller circuit, resistance readout circuit and SnO2 transducer film. The design criteria for different building blocks of the system is elaborated. The microheaters are optimized for temperature uniformity as well as static and dynamic response. The electrical equivalent model for the microheater is derived by extracting thermal and mechanical poles through extensive laser doppler vibrometer measurements. The temperature controller and readout circuit are realized on 130nm CMOS technology. The temperature controller re-uses the heater as a temperature sensor and controls the duty cycle of the waveform driving the gate of the power MOSFET which supplies heater current. The readout circuit, with subthreshold operation of the MOSFETs, is based on resistance to time period conversion followed by frequency to digital converter. Subthreshold operatin of MOSFETs coupled with sub-ranging technique, achieves ultra low power consumption with more than five orders of magnitude dynamic range. RF sputtered SnO2 film is optimized for its microstructure to achive high sensitivity to sense LPG gas.