Comprehensive Depletion-Mode Model for TFT Assessment

Abstract

A comprehensive depletion-mode model is developed to describe depletion-mode thin-film transistor (TFT) behavior [1]. This model is distinctly different than the square-law model, which accurately describes enhancement-mode TFT behavior and establishes the equations normally employed for carrier mobility extraction. In the comprehensive depletion-mode model, bulk mobility (μBULK) and interface mobility (μINT) are distinguished based on the assumption that carrier transport can occur within an accumulation layer and/or within the ‘bulk’ of the channel. In this work, the comprehensive depletion-mode model is used to estimate the mobility of p-channel TFTs and solution-processed n-channel TFTs, and also to estimate the free carrier concentration of within the ‘bulk’ of the channel when a TFT exhibits depletion-mode behavior. Simulation reveals that the estimated interface mobility of a depletion-mode TFT is often overestimated when mobility is improperly extracted using the square-law model. [1] F. Zhou et al., “Mobility assessment of depletion-mode oxide thin-film transistors using the comprehensive depletion-mode model,” ECS Journal of Solid State Science and Technology, 3(9), Q3027-Q3031 (2014)