Accurate Field-Effect Mobility and Threshold Voltage Estimation for Thin-Film Transistors with Gate-Voltage-Dependent Mobility in Linear Region

The measurement of mobility and threshold voltage in thin-film transistors (TFTs) in which the mobility is a function of gate voltage or carrier density is usually done inaccurately. Herein, accurate mobility calculations within the framework of the gradual channel approximation are described. Conventionally, the derivative of drain current with respect to gate voltage is often used to calculate mobilities in the linear region. This procedure often leads to errors when the mobility is not constant. Using a first-order finite difference-based calculations, it is shown how the correct field-effect mobility can be extracted. The corrected mobility can be smaller than the conventionally calculated field-effect mobility by up to a factor of 2. It is also shown that the corrected field-effect mobility is identical to the average mobility. A threshold voltage that is independent of gate voltage value and suitable for disordered semiconductors is used for more accurate mobility calculations. The mobility and threshold voltage calculations are illustrated with experimental data from multiple TFTs with indium gallium zinc oxide, zinc tin oxide, and molybdenum disulfide channel layers.