Atomic layer deposited SnO2/ZnO composite thin film sensors with enhanced hydrogen sensing performance

Hydrogen gas (H2) has long been regarded as a clean and renewable energy carrier alternative to the fossil fuel, therefore the development of highly sensitive and reliable hydrogen sensor is imperative for the large-scale implementation of green energy hydrogen. In this work, SnO2, ZnO thin film and SnO2/ZnO composite thin film H2 sensors were fabricated on SiO2/Si substrates by atomic layer deposition (ALD). The effect of ALD cycles and heat treatment temperatures on the sensing properties of the thin film sensors was investigated deeply. It is found that the 100-cycle SnO2/150-cycle ZnO composite film shows the best H2-sensing performance such as large response of 93 to 30 ppm H2 at 200 ℃, fast response/recovery time of 50 s/29 s, and low detection limit of 250 ppb. Moreover, the response of SnO2/ZnO composite film sensor is 10 times and 2 times higher than that of the pure ZnO and SnO2 thin film ones at working temperature of 200℃, respectively. A possible mechanism for performance improvement of the SnO2/ZnO composite film H2 sensor is proposed, attributed to the synergistic effect of the SnO2-ZnO heterojunction and the oxygen vacancies in the SnO2 film. ALD may be a feasible strategy to construct Si-based highly sensitive hydrogen sensors for micro-electromechanical system application.