Intrinsic Channel Mobility of Amorphous, In-Ga-Zn-O Thin-Film Transistors by a Gated Four-Probe Method

Intrinsic mobility and intrinsic channel resistance (R CH ) of amorphous, In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) with varying channel length (L) are investigated using a gated four-probe back-channel-etched TFT design. The intrinsic R CH is found to decrease from ~500 to ~250 kΩ per unit area by increasing V GS from 10 to 20 V. The intrinsic mobility is ~17 cm 2 /V·s, which is about 20% higher than that derived from the normal two-point probe measurements. Source and drain parasitic resistance (R PAR ) of the a-IGZO TFTs is found to be of the same order of magnitude as the R CH -which is different from hydrogenated amorphous-silicon (a-Si:H) TFTs, where TFT operation is dominated by R PAR .