Anomalous drain-induced barrier lowering effect of thin-film transistors due to capacitive coupling voltage of light-shield metal

The anomalous drain-induced barrier lowering (DIBL) effect of long-channel thin-film transistors (TFTs) with a light shield (LS) is investigated by two-dimensional (2D) device simulation. In long-channel TFTs with a LS, which is long enough to neglect the DIBL effect and the floating body effect, a decrease of threshold voltage (V_th) was observed at high drain voltages. The V_th lowering is due to the large potential of the LS induced by the high drain voltage, which lowers the height of the source potential barrier. It is found that the LS-induced DIBL effect can be larger as the length of the LS increases or the thickness of the buried oxide decreases.