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 CH4 and CO were detected successfully using this method by self-made indirectly Pt/SnO2 sensors. The results show that the response time of the Pt/SnO2 sensors is 9 s and 8 s, and the recovery time is 25 s and 23 s for 100 ppm CH4 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 CH4 and CO, are highly linear with the gas concentration without using the log coordinates. The selectivity of the Pt/SnO2 sensors for 500 ppm CH4 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/SnO2 sensors are improved by this method, and an effective detection can be realized for a wide gas concentration range of 0-500 ppm CH4 and CO. It provides a new potential detection pathway for MOS-based gas sensors.

Pt and BP co-modified WS₂ sensors were used for the first time to recognize ppb-level NO₂ at a low temperature of 50 °C. The sensor achieves satisfactory repeatability, superior selectivity, and fast response with negligible baseline drift.

Air pollution is one of the major threats to human health. The monitoring of toxic NO₂ gas in urban air emission pollution is becoming increasingly important. Thus, the development of an NO₂ sensor with low power consumption, low cost, and high performance is urgent. In this paper, a planar structural micro hotplate gas sensor based on an AlN ceramic substrate with an annular Pt film heater was designed and prepared by micro-electro-mechanical system (MEMS) technology, in which Pt/Nb/In₂O₃ composite semiconductor oxide was used as the sensitive material with a molar ratio of In:Nb = 9:1. The annular thermal isolation groove was designed around the heater to reduce the power consumption and improve the thermal response rate. Furthermore, the finite element simulation analysis of the thermal isolation structure of the sensor was carried out by using ANSYS software. The results show that a low temperature of 94 °C, low power consumption of 150 mW, and low concentration detection of 1 to 10 ppm NO₂ were simultaneously realized for the Nb-doped In₂O₃-based gas sensor. Our findings provide a promising strategy for the application of In₂O₃-based sensors in highly effective and low concentration NO₂ detection.