Conduction model of coupled domination by bias and neck for porous films as gas sensor

A conduction model valid for porous films was proposed in the condition that the transport behavior of the carriers was controlled by the coupled dominant mechanism with the existence of the bias and necks in the grain boundary. The characteristics of the necks can be described accurately by two important morphological parameters: the average neck width W¯n and the average density of neck in the unit area P¯n. Both parameters were controlled by different sintering temperatures, and further optimized by statistical calculations based on the observations of the stereology derived from the FE-SEM images. The basic physical parameters: the barrier potential VB and the depletion width Wn, were acquired by multi-parameter fitting based on I-V curves measured in dry air and methanol atmosphere. In this article, to elucidate the rationality of the conduction model, zinc oxide served as the sensitive porous layer, and I-t characteristics were evaluated. By using the physical parameters in conduction model, the valve effect was proposed to illustrate the diversity of response to methanol for ZnO porous films fabricated at different sintering temperatures. The valve control coefficient Y reveals the fact that only a suitable neck width has dominating contribution to the gas response.