Oxygen Flow Effects on Electrical Properties, Stability, and Density of States of Amorphous In-Ga-Zn-O Thin-Film Transistors
Yong-Su Lee, Eric K.-H. Yu, Linsen Bie, and Jerzy Kanicki
We varied the oxygen flow rate during the sputtering of a-IGZO thin films and studied its impact on a-IGZO DOS and TFT electrical properties including stability under both PBTS and negative BTS (NBTS).
We found that the excess oxygen content can significantly impact a-IGZO TFT electrical characteristics. High PO2 reduces TFT field-effect mobility and Ion and increases Vth. When undergoing PBTS (Vst = +10 V), higher PO2 corresponds to larger ΔVth, while no clearly discernable trend is observed for NBTS. The sub-gap DOS of a-IGZO are decomposed into exponential bandtail states and Gaussian-like deep-gap states, according to the DOS model we have adopted. The peak density of the Gaussian-like distributions is larger for higher PO2 during deposition. Assuming that high PO2 during deposition is associated with incorporation of excess/weakly-bonded oxygen in the a- IGZO thin film, then we can conclude that these deep- gap states are acceptor-like electron trap states in the form of O0 or O1- ions.
