Preparation of high performance Fe-doped SnO2 humidity sensor and its application in respiration detection

A humidity sensor with high performance based on Fe3+ ions doped with SnO2 (Fe/SnO2) was synthesized by hydrothermal method and its mechanism was studied by the first principle based on density functional theory. Experimental results show that doping Fe3+ ions can effectively improve the performance of SnO2 humidity sensor. Compared with SnO2, the resistance of Fe/SnO2 humidity sensor increases from 4.5 to 5.5 orders of magnitude, the humidity hysteresis error decreases from 42.4% to 3.8% and the response/recovery time changes from 11 s/48 s–10 s/8 s. Calculations show that Fe3+ ions can enhance the chemical and physical adsorption energy, improving the sensitivity and linearity and reducing the hysteresis error and recovery time of SnO2, respectively. Moreover, a simple circuit for respiratory detection was designed based on Fe/SnO2, and the number of LED lights can distinguish different breathing states through resistance changes of the Fe/SnO2 humidity sensor. This study indicate Fe/SnO2 humidity sensor can be used in non-contact and visual breath detection, which has potential applications in preventing respiratory disease.