Vertically Graded Oxygen Deficiency for Improving Electrical Characteristics and Stability of Indium Gallium Zinc Oxide Thin-Film Transistors

We investigated a facile fabrication method, which is an insertion of a carrier-induced interlayer (CII) between the oxygen-rich a-IGZO channel and the gate insulator to improve the electrical characteristics and stability of amorphous indium–gallium–zinc–oxide thin-film transistors (a-IGZO TFTs). The a-IGZO channel is deposited with additional oxygen gas flow during a-IGZO channel deposition to improve the stability of the a-IGZO TFTs. The CII is a less than 10 nm thick deposited thin film that acts to absorb the oxygen from the a-IGZO front channel through oxidation. Through oxidation of the CII, the oxygen concentration of the a-IGZO front channel is decreased compared to that of the oxygen-rich back channel, which forms a vertically graded oxygen deficiency (VGO) in the a-IGZO channel. Therefore, the electrical characteristics of the VGO TFTs are improved by increasing the carrier concentration of the front channel as the oxygen vacancy concentration in the front channel is increased through the oxidation of the CII. At the same time, the stability of the VGO TFTs is improved by maintaining a high oxygen concentration in the back channel even after oxidation of the CII. The field-effect mobility (μFET) of the VGO TFTs improved compared to that of the a-IGZO TFTs from 7.16 ± 0.6 to 12.0 ± 0.7 cm2/V·s. The threshold voltage (Vth) shifts under positive bias temperature stress and negative bias temperature illumination stress decreased from 6.00 to 2.95 V and −15.58 to −8.99 V, respectively.