Appropriate choice of channel ratio in thin-film transistors for the exact determination of field-effect mobility

Field-effect mobilities are the most important figures of merit to evaluate the feasibility of semiconductors for thin-film transistors (TFTs). They are, however, sometimes extracted from TFTs with the active semiconductor area undefined and in small channel ratios without the effect of the fringing electric field at the ends of source/drain electrodes taken into account. In this letter, it is demonstrated that the field-effect mobilities extracted from undefined nanoparticulate zinc oxide (ZnO) TFTs at the channel ratio of 2.5 are overestimated by 418%, and the choice of large channel ratios gives the real value of field-effect mobilities.