Simulation of the backward current in polycrystalline silicon thin-film transistors

Many of previous electrical simulations of the channel current under reverse bias conditions in a polycrystalline silicon thin film transistors assume an homogeneous material with an uniformly distributed defect density. Nevertheless, polycrystalline silicon, particularly laser crystallised silicon, is an inhomogeneous material with large crystallised regions, the grains, and disordered thin interfaces, the grain boundaries. Within the device simulator Atlas, we introduced this more realistic model of polycrystalline material, with monocrystalline grains of size L, separated by amorphous grain boundaries of size e, to reproduce the reverse current behaviour of polysilicon thin film transistors. The experimental reverse current generally shows an exponential increase versus the reverse bias. With the introduction of a generation model with carriers band to band tunnelling, the exponential behaviour of the backward channel current with respect to the reverse bias voltage can be accounted for.