The effect of the material morphology on the response of the NO2 sensor based on ZnO thin film

A non-typical maximum in the dependence of the response of the NO2 sensor based on ZnO film on the film thickness is observed. This behaviour is associated with the effect of the microstructure on the sensor response, particularly the effect of the variation of the film porosity is considered. The change of the film porosity can modify the film permeation to the target gas and this process competes with the change of the active surface area when varying the sensor active layer thickness. The behaviour of the sensor response with the film thickness is simulated by assuming the Knudsen diffusion of gas molecule through the film pores and a first-order kinetic for the surface reactions. A correlation between the pore radius and thickness of sensor active layer is proposed according with the experimentally observed change of the film porosity with the thickness.