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

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 cm² V·s⁻¹ suffer from severe short channel effects at L_g = 1 µm 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 ΔL 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 ΔL and physically increase L_eff, 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.