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This paper presents modeling and parameter extraction of the above-threshold characteristics of hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) in both linear and saturation regions of operation. A bias- and geometry-independent definition for field effect mobility considering the ratio of free-to-trapped carriers is introduced, which conveys the properties of the active semiconducting layer. A method for extraction of model parameters such as threshold voltage, effective mobility, band-tail slope, and contact resistance from the measurement results is presented. This not only provides insight to the device properties, which are highly fabrication-dependent, but also enables accurate and reliable TFT circuit simulation. The techniques presented here form the basis for extraction of physical parameters for other TFTs with similar gap properties, such as organic and polymer TFTs.
Date of Publication: Nov. 2003