Impacts of channel film thickness on poly-Si tunnel thin-film transistors

Abstract

Performance improvement of polycrystalline-silicon (poly-Si) tunnel field-effect transistors (TFETs) by the channel thickness reduction is proposed and compared with conventional poly-Si thin-film transistors (TFTs). The thickness reduction of poly-Si film would have smaller grain size and higher trap state density, resulting in the driving current degradation ~33% of conventional poly-Si TFTs due to the degradation of field-effect mobility. However, the poly-Si TFETs with thinner poly-Si channel film exhibit better subthreshold swing from 0.545 V/decade to 0.365 V/decade and ~70% improvement of driving current when the channel film thickness is decreased from 100-nm to 50-nm. It indicates the enhancement of gate-to-junction control ability has stronger impacts than the effect of trap state density generation on the interband tunneling current of the poly-Si TFETs. Consequently, it is an easy way to improve the performance of poly-Si TFETs and can be easily combined with other performance improvement techniques of poly-Si TFETs.