Threshold voltage reduction and mobility improvement of LTPS-TFTs with NH₃ plasma treatment

In this paper, NH₃ plasma directly applied to the surface of poly-Si channel is studied for the development of high-performance low-temperature polycrystalline-silicon thin-film transistors (LTPS-TFTs) with HfO₂ high-\kappa gate dielectric. The reduction of threshold voltage from 1.52 to 0.62 V, the decrease of subthreshold swing from 227 to 151 mV/decade, and the enhancement of field effect mobility μ FE from 31 to 65 cm ²/Vs are observed after NH₃ plasma surface treatment. It can be attributed to the NH₃ plasma surface treatment enabling defect passivation and plasma-induced interfacial layer (PIL) growth. To decouple the impacts of defect passivation and PIL growth, the device without PIL is also fabricated. This paper demonstrates the important impacts of NH₃ plasma surface treatment on the improvement of electrical characteristics of LTPS-TFTs.