Low-frequency noise in offset-gated polysilicon TFTs

The low-frequency noise in offset-gated polysilicon thin-film transistors (TFTs) is investigated. It is shown that the spectral density of the drain current fluctuations can be interpreted in terms of the carrier number fluctuations, considering the extrinsic transconductance of the device. The relation between the extrinsic transconductance of the offset-gated polysilicon TFT and the intrinsic transconductance of the self-aligned device was found to depend mainly on the polysilicon layer quality. An effective density of traps N_teff^* was extracted which reflects the contribution to the noise of the active and passive channel. The extracted noise index N_teff^* is lower when the polysilicon layer quality is improved (lower in-grain defect density).