Degradation Model of a-IGZO TFT due to High Drain Bias Stress

Abstract

In this paper, the TCAD degradation model of IGZO using spatial distribution (X, Y) of physical parameters is proposed for the first time and is confirmed according to various channel length, active thickness, and bias stress conditions that agree with actual measurements. The asymmetric degradation phenomenon according to the source/drain sweep direction occurs when high VDS stress (> 40 V) is applied to a-IGZO TFT due to the local strong electric field in the drain edge region in the active channel. In the double side gate (DSG) structure, the degree of degradation varies according to VTG, which is influenced by the concentration of electrons induced in the channel. Oxygen vacancy in the presence of 2+ ionized states (VO2+) in IGZO is stable. However, when band bending is severe, the electrons are captured, and the structural transition occurs as a neutral VO in the meta-stable state. This process is assumed to be a mechanism of IGZO degradation at high drain bias stress, and the electric field (>0.5M V/cm) and electron concentration (>1 × 1010 cm−3) in the channel are considered as the main factors of degradation and are modeled using the mapping function provided by Silvaco.