A threshold voltage definition for modeling asymmetric dual-gate amorphous InGaZnO thin-film transistors with parameter extraction technique

A physical definition of threshold voltage has been proposed for asymmetric dual-gate amorphous InGaZnO (a-IGZO) thin-film transistors. Based on the definition, a compact model for drain current has been derived with complete parameter extraction methods. According to the distribution characteristics of density of states (DOS) in the a-IGZO bandgap, the threshold voltage of bottom-gate (BG)-driven devices is defined by the ratio of the trapped-carrier density to the free-carrier density at the bottom surface of the channel layer. This definition has proven to give appropriate values of threshold voltage for devices with DOS parameters varying in a wide range. The trapped-charge density in the above-threshold region can be expressed based on the defined threshold voltage, with the form related to the BG voltage, the top-gate voltage, and the potential along the channel. The free-charge density and analytical drain current can thus be obtained in the above-threshold region. Finally, the continuous drain current expression is developed covering all operation regions. In the modeling process, the determination and extraction strategies for parameters are also presented. Published under license by AIP Publishing.