Intrinsic Channel Mobility of Amorphous, In–Ga–Zn–O Thin-Film Transistors by a Gated Four-Probe Method
Intrinsic mobility and intrinsic channel resistance $(R_{\rm CH})$ 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 $R_{\rm CH}$ is found to decrease from ${\sim}{500}$ to ${\sim}{\rm 250}~{\rm k}\Omega$ per unit area by increasing $V_{\rm GS}$ from 10 to 20 V. The intrinsic mobility is ${\sim}{\rm 17}~{\rm cm}^{2}/{\rm V}\cdot{\rm s}$ , which is about 20% higher than that derived from the normal two-point probe measurements. Source and drain parasitic resistance $(R_{\rm PAR})$ of the a-IGZO TFTs is found to be of the same order of magnitude as the $R_{\rm CH}$ —which is different from hydrogenated amorphous-silicon (a-Si:H) TFTs, where TFT operation is dominated by $R_{\rm PAR}$ .