Geometric Effect Elimination and Reliable Trap State Density Extraction in Charge Pumping of Polysilicon Thin-Film Transistors

The charge pumping (CP) technique in polysilicon thin-film transistors (TFTs) is optimized by adjusting the gate pulse transition times to eliminate the geometric component of the CP current. Improved CP curves similar to those in MOSFETs are obtained for polysilicon TFTs. Typical trap state density (D macrt) energy distribution within the upper part of the band gap and the mean Dt value ([(D macr)]t) are reliably extracted in different approaches. Furthermore, based on the traditional CP model, a modified Dt extraction approach, where the influence of the CP geometric component is inherently avoided, is first proposed. Such an extracted [(D macr)]t agrees well with those extracted by two optimized conventional approaches where geometric effect is eliminated.