Time-dependent oxygen vacancy distribution and gas sensing characteristics of tin oxide gas sensitive thin films

The model of gradient distributed oxygen vacancies is extensionally investigated. Based on the dynamics of oxygen vacancies under diffusion and exclusion effects in cooling process, the steady state and non-steady state solutions of the diffusion equation of the vacancies are solved. The transient distribution of oxygen vacancies is revealed during the idealized cooling process. It is concluded that the exclusion effect dominates the density distribution of oxygen vacancies throughout the crystallite. The time-dependent expressions of potential barrier [qV(x,t)], film resistance (R) and response to reducing gases (S) are formulated on the basis of Schottky model and Poisson's equation. The simulated gas sensing characteristics are in good correlation with experimental results. The constants and variables are estimated according to the correlation. Presumptions and reservations of the present expressions are also discussed.