Origin of low-frequency noise in polycrystalline silicon thin-film transistors

Low-frequency drain current fluctuation noise was measured in a series of polycrystalline silicon thin-film transistors (polysilicon TFTs), characterized by an average grain size L-g and in-grain defect density D-in. In one type of polysilicon TFT, D-in is low (about 5 x 10(8) cm(-2)) and L-g varies from about 67 to 145 nm. In another type of polysilicon TFT, L-g remains constant (about 2.5 mum) and D-in varies from about 5 x 10(12) to 5 x 10(10) cm(-2). It is demonstrated that the noise originates from fluctuations of carriers due to carrier capture/release processes: (a) in traps located near the polysilicon/SiO2 interface and (b) in traps located at the grain boundaries. The polysilicon/SiO2 interface is distinguished from that of the crystalline silicon/SiO2 by comprising the in-grain traps, in addition to the oxide traps. The proposed carrier number fluctuation model, sufficient to explain noise in polysilicon TFTs, is closely related to the structural parameters L-g and D-in of the polysilicon layer. (C) 2002 American Institute of Physics.