(Invited) Hydrogen-Related Trap States Induced during Fabrication Process and Annealing Effects in Amorphous in-Ga-Zn-O Thin Film Transistors

Abstract

Metal compositions and electronic structures near the back channel surfaces of amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) were investigated by means of x-ray photoelectron spectroscopy (XPS) and photoinduced transient spectroscopy (PITS). The Zn deficient states were observed near the back channel surface due to S/D over-etching in BCE process. In the a-IGZO back channel region with the Zn deficient states, it was indicated that positively charged interface states, which induced a negative-parallel shift in transfer curves were easily formed by desorption of hydrogen adsorbed at the interface, and hydrogen-related trap states causing a negatively hump-shaped Vth shift were formed in the a-IGZO bulk by diffused hydrogen atoms from the interface and/or a passivation layer (PVL). In addition, a post-annealing treatment at higher temperatures was found to be effective to reduce the density of the defects in both the a-IGZO bulk and the PV/a-IGZO interface.