Effect of ${rm O}_{2}$ Flow Rate During Channel Layer Deposition on Negative Gate Bias Stress-Induced $V_{rm th}$ Shift of a-IGZO TFTs

摘要

The effect of ${rm O}_{2}$ flow rate during the sputtered deposition of channel layer on the negative gate-bias stress (NGBS)-induced threshold voltage $(V_{rm th})$ instability of a-IGZO TFTs is investigated. It is shown that the negative gate-bias stress results in a negative $V_{rm th}$ shift of the a-IGZO TFTs, and the shift amount decreases with the increase in ${rm O}_{2}$ flow rate. It is proposed that the $V_{rm th}$ shift originates from the electron-detrapping from the oxygen vacancy-related donor-like states at the channel/dielectric interface. As the ${rm O}_{2}$ flow rate increases, the density of donor-like states is decreased and the distribution of neutral donor-like states below $E_{F}$ is also reduced. Therefore, the amount of $V_{rm th}$ shift caused by the positively charged trap states and electrons injecting into the channel from the donor-like states decreases with the ${rm O}_{2}$ flow rate increase. It is also shown experimentally that while the electrical characteristics of the a-IGZO TFTs are generally improved with the ${rm O}_{2}$ flow rate increase, they are degraded if an excess ${rm O}_{2}$ is introduced. An optimal ${rm O}_{2}$/Ar flow rate rat- o of about 5 sccm/45 sccm is suggested to make a trade-off between the electrical performances and the gate-bias stress-induced $V_{rm th}$ instability.