Room temperature hydrogen response kinetics of nano–micro-integrated doped tin oxide sensor

The nano–micro-integrated sensor has been fabricated by sol–gel depositing the nanocrystalline indium oxide (In₂O₃)-doped tin oxide (SnO₂) thin film on microelectromechanical systems (MEMS) device having interdigitated electrode configurations with two different electrode spacing (10 μm and 20 μm) and two different number of fingers (8 and 20). The present nano–micro-integrated sensor exhibits high H₂ sensitivity range (S = 3–10⁵) for the H₂ concentration within the range of 100–15,000 ppm at room temperature. It has been demonstrated that, the room temperature response kinetics of the present nano–micro-integrated sensor is a function of finger spacing, H₂ concentration and air-pressure, but independent of number of fingers. Such dependence has been explained on the basis of Le Chatelier's principle applied to the associated H₂ sensing mechanism and the role of above parameters in shifting the dynamic equilibrium of the involved surface reactions under the described test conditions. A new definition of the response time has been proposed, which is not only suitable for the theoretical analysis but also for the practical applications, where a gas-leak detection alarm is required to be triggered.