Optimized Low Frequency Temperature Modulation for Improving the Selectivity and Linearity of SnO<sub>2</sub> Gas Sensor
Wenjie Zhao, Kai-Lun Ding, Yinsheng Chen, Fang-Ying Xie, Dan Xu
Abstract
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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> and CO were detected successfully using this method by self-made indirectly Pt/SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensors. The results show that the response time of the Pt/SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensors is 9 s and 8 s, and the recovery time is 25 s and 23 s for 100 ppm CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> and CO, are highly linear with the gas concentration without using the log coordinates. The selectivity of the Pt/SnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensors for 500 ppm CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> 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 <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sensors are improved by this method, and an effective detection can be realized for a wide gas concentration range of 0-500 ppm CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> and CO. It provides a new potential detection pathway for MOS-based gas sensors.