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
.