Analysis of threshold voltage of short channel polycrystalline silicon thin-film transistors fabricated on large grains

Drain bias dependence of threshold voltages of short channel thin-film transistors (TFTs) fabricated on polycrystalline silicon (poly-Si) films with large grains has been investigated. The drain coefficient of the threshold voltage was found to be substantially larger in poly-Si TFTs than that in metal-oxide-semiconductor field-effect transistors on a silicon-on-insulator wafer. In addition, the drain coefficient of poly-Si TFTs shows asymmetric behavior with respect to source-drain swapping. The observed results can be explained in terms of body potential modulation caused by accumulation of excess holes generated by impact ionization and drain junction leakage. The asymmetry in drain coefficient with source-drain swapping can be attributed to the difference in the bipolar gain between the source-body and drain-body junctions.