Carrier transport and instability mechanisms in oxide semiconductor thin film transistors

The growing demand for amorphous oxide semiconductor thin film transistors (TFT) necessitates the development of a physics-based field-effect mobility model that links the terminal characteristics of TFTs to their material properties. This need is particularly acute since existing approaches fail to explicitly account for the unique carrier transport properties of oxide semiconductors. The first part of this thesis specifically addresses this challenge. Here, it is shown that the electron conduction mechanism in the above-threshold regime of amorphous oxide semiconductor TFTs is controlled by both percolation and trap-limited conduction. In the limit where trap-limited conduction prevails, the characteristic temperature of tail states controls the field-effect mobility; whereas in the limit where percolation prevails, the properties of conduction’s band potential fluctuation govern it. Irrespective of the operation regime, the fieldeffect mobility is found to follow a power law form. The value of the trap density plays a critical role in determining the transition voltage. This is because a high value leads to Fermi level pinning, and thus trap-limited conduction dominates; whereas a low value results in percolation since the Fermi level becomes able to cross the conduction band edge for trap density of