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

Intrinsic mobility and intrinsic channel resistance (RCH) 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 RCH is found to decrease from similar to 500 to similar to 250 k Omega per unit area by increasing VGS from 10 to 20 V. The intrinsic mobility is similar to 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.