Mechanism Analysis of Off-Leakage Current in Poly-Si TFTs with LDD Structure

We have analyzed the mechanism of off-leakage current in a lightly doped drain (LDD) poly-Si thin film transistor (TFT) structure using a two-dimensional device simulation and by evaluating the temperature dependence. The off-leakage current in the self-aligned TFTs is mainly caused by band-to-band tunneling, and the off-leakage current in the LDD TFTs is mainly caused by phonon-assisted tunneling with the Poole–Frenkel effect. The carrier generation mostly occurs near the intersection of the front-insulator interface and the interface between the LDD and drain regions because both the electron and hole densities are simultaneously low and the electric field is strong.