Optimized Low Frequency Temperature Modulation for Improving the Selectivity and Linearity of SnO2 Gas Sensor

The disadvantages of poor selectivity, thermal instability and nonlinear output for metal oxide semiconductor (MOS) gas sensors restrict their detection accuracy for flammable and toxic gases. In this paper, a low frequency dynamic temperature modulation detection method using rectangular wave was designed and first proposed herein. The temperature modulation detection mechanism was also provided in detail. The flammable gases CH ₄ and CO were detected successfully using this method by self-made indirectly Pt/SnO ₂ sensors. The results show that the response time of the Pt/SnO ₂ sensors is 9 s and 8 s, and the recovery time is 25 s and 23 s for 100 ppm CH ₄ and CO, using the rectangular wave temperature modulation with a working temperature of 335-382 °C and an optimized frequency of 100 mHz. The temperature modulation has more advantages than steady-state constant temperature method in power consumption and working temperature. The temperature-modulated response for CH ₄ and CO, are highly linear with the gas concentration without using the log coordinates. The selectivity of the Pt/SnO ₂ sensors for 500 ppm CH ₄ and CO is enhanced from 2.03 using the traditional steady-state constant temperature detection to 2.56 using the temperature modulation method. Compared with the steady-state constant temperature method, both the selectivity and linearity of the response output for the Pt/SnO ₂ sensors are improved by this method, and an effective detection can be realized for a wide gas concentration range of 0-500 ppm CH ₄ and CO. It provides a new potential detection pathway for MOS-based gas sensors.