Low-frequency noise in low temperature unhydrogenated polysilicon thin film transistors

Low-frequency noise measurements are performed in two types of low temperat ure polysilicon thin film transistors (TFTs), For the first TFT process, th e polysilicon two layer structure induces large values of the channel acces s resistances, whose contribution to noise is dominant for large gate bias. For the second TFT process, the polysilicon single layer structure induces small access resistances and the measured noise is mainly due to channel s ources, For small voltages, the channel noise spectral density evolution wi th gate bias agrees with the mobility fluctuation model and is identical fo r both processes. For large voltages (>2 V), the channel noise spectral den sity evolution, observed only in the case of the single layer structure, se ems to agree with the fluctuations of carrier density. However, this interp retation is discussed. The results of static characterization show that the quality of the channel active layer is quite different from the two layer structure to the single layer structure. In agreement with these observatio ns, the observed evolution of the relative noise with increasing gate bias in TFTs can be interpreted from intergrain potential lowering. (C) 2000 Els evier Science Ltd. All rights reserved.