Heterojunction channel engineering to enhance performance and reliability of amorphous In–Ga–Zn–O thin-film transistors

Abstract

Heterojunction channel engineering is discussed as a means of enhancing the performance and bias stress stability of In–Ga–Zn–O thin-film transistors (IGZO TFTs). A heterojunction channel was formed by depositing In-rich IGZO on IGZO111 with an atomic ratio of In:Ga:Zn=1:1:1, whose energy band lineup was type-II with a potential well of 0.4 eV for electrons. The thickness of the bottom IGZO111 layer strongly affected the field-effect mobility (μFE) of the TFT owing to electron confinement effect at the heterojunction interface. μFE was enhanced from 12.4 cm2 V−1 s−1 for homogeneous IGZO111 TFT to 24.7 cm2 V−1 s−1 for the heterojunction TFT. Device simulation results revealed that electron confinement in the heterojunction channel played an important role in determining μFE in the TFT. A channel engineering approach will provide a method of overcoming the trade-off between μFE and the positive-bias stress stability of oxide TFTs.