Optimizing Length Scalability of InGaZnO Thin-Film Transistors through Lateral Carrier Profile Engineering and Negative Δ<i>L</i> 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 (L-eff) and length scalability even when the physical gate length (L-g) is the same. Especially, devices with high carrier concentration that have a high mobility of 14.54 cm(2) V<middle dot>s(-1) suffer from severe short channel effects at L-g = 1 mu m due to the reduced L-eff. The current work proposes a systematic methodology for optimizing length scalability for a given L-g that involves engineering of the lateral carrier profile. Unique lateral carrier profiles are extracted using contour maps of Delta L and R-SD as a function of carrier profile parameters, and they are validated by comparing the measured L-eff, 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 V-T roll-off that occurs with increasing carrier concentration, an IGZO TFT with gate-insulator shoulders is fabricated to structurally form negative Delta L and physically increase L-eff, while also obtaining a high carrier concentration, ultimately achieving both optimal electrical performance, with mobility of 17.50 cm(2) V<middle dot>s(-1), and complete control of the electrostatic integrity of the gate.