Capping Ti-Doped GaZnO on InGaZnO Layer As the Composite-Channel Structure for Enhancing the Device Performances and Stability of Thin-Film Transistors

The device performances of an amorphous indium gallium zinc oxide transparent thin-film transistor (a-IGZO TFT) were improved by using a Ti-doped GaZnO (GTZO) as the channel capping layer in this study. The GTZO thin film exhibited a high carrier concentration of 1.5 × 10
²¹
cm
^-3
and served as both a carrier supplement and passivation layer for reducing the absorption of oxygen and moisture as well as the back-channel charge trapping in the composite-channel TFT. An enhanced carrier mobility with high electron concentration in the composite GTZO/IGZO heterostructure was verified in the Hall measurement. The GTZO/IGZO composite-channel TFT was demonstrated to show an improved carrier mobility of 15.5 cm
²
/V-s, subthreshold swing of 0.35 V/decade, off current of 1.4 × 10
^-11
A, threshold voltage of 1.4 V, and ON/OFF current ratio of 1.2 × 10
⁷
. Stable operation with unchanged device characteristics was observed following a bias-stress test. Thus, the fabricated GTZO/IGZO TFTs exhibited advantageous device performance and improved device operation stability.