Analysis of Effective Channel Length in Amorphous Silicon Thin-Film Transistors

This paper analyzes the effective channel length in amorphous silicon thin-film transistors ( a -Si TFTs) by examining the parasitic channel length, Δ L , which causes the apparent dependence of the field-effect mobility of TFTs on the nominal channel length. The parasitic channel length is found to depend on the a -Si thickness, L a , at the source path and the drain path of TFTs if there is no etching stopper insulator on the a -Si layer. An analytical formula for the parasitic channel length is derived by assuming that the space-charge-limited current is the dominant conduction mechanism through these paths. The validity of the analysis is confirmed by applying the formula to the experimental results on the Δ L - L a relationship for a range of L a between 0.18 and 0.98 µm.