Intrinsic Channel Mobility Associated with Extended State Transport in IGZO TFTs

Abstract

There is wide variation in the interpretation of the interaction and/or independence of channel mobility and charge trapping in IGZO TFTs. Electrical measurements reveal temperature-dependent behavior that is not explained by existing TCAD models employed for defect states and carrier mobility. An IGZO TFT device model has been recently developed using Silvaco Atlas, which accounts for the role of donor-like oxygen vacancy defects, acceptor-like BTS, and acceptor-like interface traps, thus properly regulating the amount of free channel charge. The channel mobility is defined as only a function of temperature, and reflects a thermally-activated diffusive mobility with a distinct activation energy Ea = 40 meV. This thermally activated process is clearly intrinsic, as it is constant over all bias conditions and is not dependent on the steady-state trapped charge level. The model demonstrates a remarkable match to transfer characteristics measured at T = 150 K to room temperature.