Optimizing Length Scalability of InGaZnO Thin-Film Transistors through Lateral Carrier Profile Engineering and Negative ΔL Extension Structure

Abstract

The lateral carrier profile of amorphous indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) plays a significant role in determining the effective channel length (Leff) and length scalability even when the physical gate length (Lg) is the same. Especially, devices with high carrier concentration that have a high mobility of 14.54 cm2 V·s−1 suffer from severe short channel effects at Lg = 1 µm due to the reduced Leff. The current work proposes a systematic methodology for optimizing length scalability for a given Lg that involves engineering of the lateral carrier profile. Unique lateral carrier profiles are extracted using contour maps of ΔL and RSD as a function of carrier profile parameters, and they are validated by comparing the measured Leff, drain-to-source resistance, and current-voltage characteristics with the results of simulations using the extracted carrier profiles. Further, to overcome the trade-off between enhanced mobility and degraded VT roll-off that occurs with increasing carrier concentration, an IGZO TFT with gate-insulator shoulders is fabricated to structurally form negative ΔL and physically increase Leff, while also obtaining a high carrier concentration, ultimately achieving both optimal electrical performance, with mobility of 17.50 cm2 V·s−1, and complete control of the electrostatic integrity of the gate.