Thermal effects in oxide TfTs

In oxide-based thin films transistors (TFTs) there have been many devices reported with non-negligible output conductance. It has been proposed that the origin of the output conductance may be similar to for short channel Si MOSFETs. However, for these and the vast-majority of published oxide TFTs the channel length is more than 30x longer than the gate oxide thickness, and short channel effect are expected to be small. We have modeled ZnO TFTs with varying channel length using Synopsis Sentaurus, a 2-D drift-diffusion simulation tool, and find only small output conductance for channel lengths in the range typically reported, thus short channel effects cannot account for the output conductance in the reported oxide transistors. We do however find a correlation between input power and output conductance nearly independent of channel length for various oxide devices which suggests that self-heating may be the cause.