Mobility behavior and models for fully depleted nanocrystalline ZnO thin film transistors

Transport mechanisms in nanocrystalline ZnO Thin Film Transistors (TFT) were investigated in a wide temperature range. The channel is located at the ZnO–SiO2 interface and controlled with a bottom gate as in a back-channel SOI MOSFET. In this work, we propose suitable mobility models that are able to provide a good agreement with the experimental results. Not only do these models account for the regular carrier transport mechanisms but they also address the physical properties of nanocrystalline ZnO films including the effect of grain boundaries. Simple parameter extraction techniques are explored and validated with numerical calculations. Our work highlights that nanocrystalline ZnO TFT provides high mobility, low threshold voltage and reasonable subthreshold swing due to good interface quality between the ZnO film and the gate insulator. The variation of these parameters at low temperature is measured and compared to the typical behavior in SOI MOSFETs.