A new analytic model for amorphous silicon thin-film transistors

We present a new theory describing current-voltage characteristics of amorphous silicon thin-film transistors. We calculate the output conductance in saturation by considering channel shortening effects caused by the space-charge-limited current in the pinch-off region. In this model the drain current is expressed through the free-carrier concentration at the source side of the channel. This allows us to obtain an accurate description of the different operating regimes of a thin-film transistor using one equation that accounts for the dependence of the free-carrier concentration in the channel for different regimes. Our model is in good agreement both with experimental data and the results of our two-dimensional computer simulation. This approach allows one to account for different distributions of localized states in the energy gap. The model has also been developed to be incorporated into a circuit simulator and used for computer-aided design of amorphous silicon integrated circuits.