Novel Degradation Model of Igzo TFT on 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. Oxygen vacancy in the presence of 2+ ionized states (VO 2+) 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 (>1x1010 cm-3) in the channel are considered as the main factors of degradation and are modeled using the mapping function provided by Silvaco. Fig.1 show that the flow of development of degradataion model using TCAD. Based on the oxide degradation mechanism, the following mathematical model was proposed to determine the number of electrons captured by the electric field, Ɛ(X,Y) and the electron concentration n(X,Y) at each position in the oxide film according to equation 1. Here, ƐC and nc represent the critical electric field and electron concentration at which the deterioration starts, respectively, and 0.5 M V/cm and 1x1010 /cm3. ƐC represents the minimum energy required for metastable transition to the metastable state, and nc is a threshold value that rapidly increases the probability of occurrence of this event. These parameters can be very important physically, but they are now empirically derived from the measurement results. Figure 1