Threshold voltage dependence on channel length in amorphous-indium-gallium-zinc-oxide thin-film transistors

A threshold voltage (V-th) dependence on channel length (L) is reported for amorphous-indium-gallium-zinc-oxide thin-film transistors (TFTs). V-th is found to shift negatively with decreasing L and the negative shift is drastic in TFTs with L < 4 mu m. Combined analysis of current-voltage (I-V) and capacitance-voltage (C-V) curves shows that the Fermi energy (E-F) at flat band shifts towards the conduction band (E-C) with decreasing L, hence the negative V-th shift. Using the same analysis, the flat band carrier density (n(FB)) is also found to increase with decreasing L, revealing unintentional doping of the channel by carrier diffusion from the n(+) doped source and drain regions as the cause of the negative V-th shift. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4793996]