Modeling of amorphous-silicon thin-film transistors for circuit simulations with SPICE

Abstract

A static and dynamic model for amorphous silicon thin-film transistors is presented. The theory is based on an assumed exponential distribution of the deep states and the tail states in the energy gap. Expressions are derived that link the density of the localized states and the temperature to the drain current and the distribution of the charge in the transistor channel. In addition the authors take into account parasitic effects such as channel length modulation, off-resistance, drain and source resistances, mobile and free charges in the insulator, surface states, and overlap capacitances. The model is incorporated into the circuit simulation program SPICE. Charge conservation problems are overcome by using a charge-oriented dynamic transistor model. Simulated and measured current-voltage characteristics agree well. A 96-b gate line driver for addressing liquid-crystal displays, which was successfully designed and optimized with the model, is introduced.