In order to model dc characteristics of $n$ -channel amorphous InGaZnO thin-film transistors from experimentally obtained density of states (DOS), the acceptorlike DOS is extracted from the optical response of capacitance-voltage characteristics and confirmed by the technology computer-aided design (TCAD) simulation comparing with the measured data. Extracted DOS is a linear superposition of two exponential functions (tail and deep states), and its incorporation into TCAD model reproduces well the experimental current-voltage characteristics over the wide range of the gate and drain voltages. The discrepancy at higher gate voltage is expected to be improved by incorporating a gate voltage-dependent mobility in the model.

The effect of oxygen content on current-stress-induced instability was investigated in bottom-gate amorphous InGaZnO (a-IGZO) thin-film transistors. The observed positive threshold voltage shift (ΔV_T) was dominated by electron trapping in the gate insulator (GI), whereas it was compensated by donor creation in a-IGZO active regions when both current flows and a high lateral electric field were present. Stress-induced ΔV_T increased with increasing oxygen content irrespective of the type of stress because oxygen content influenced GI quality, i.e., higher density of GI electron traps, as well as typical direct current (DC) performance like threshold voltage, mobility, and subthreshold swing. It was also found that self-heating became another important mechanism, especially when the vertical electric field and channel current were the same, independent of the oxygen content. The increased ΔV_T with oxygen content under positive gate bias stress, positive gate and drain bias stress, and target current stress was consistently explained by considering a combination of the density of GI electron traps, electric field relaxation, and self-heating-assisted electron trapping.

In this study, the oxygen flow rate (OFR) dependence of negative bias illumination stress (NBIS) and positive bias stress (PBS) in amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) devices was investigated. Unlike in previous studies, our study simultaneously considered and analyzed the bias stress-induced degradation mechanisms by charge trapping and defect creation. NBIS and PBS instability were measured according to the OFR splits of bottom-gate (BG) IGZO TFTs and the behavior of full subgap range density of states (DOS) was experimentally tracked with especial emphasis on deep-level oxygen vacancy ( ${V}_{\text {O}}$ ) peak. It was found that the observed DOS variation was consistent with the ${V}_{\text {O}}$ ionization model during NBIS. In addition, the threshold voltage shift by charge trapping ( ${\Delta } {V}_{\text {T,CT}}$ ) and the threshold voltage shift by defect creation, i.e., change of DOS, ( ${\Delta } {V}_{\text {T,DOS}}$ ) were separated and extracted through the subthreshold slope decomposition method. After NBIS, the threshold voltage shift ( ${\Delta } {V}_{\text {T}}$ ) was composed of a component by charge trapping and a component with the ionization of ${V}_{\text {O}}$ . After PBS, ${\Delta } {V}_{\text {T}}$ was dominated by a component arising due to charge trapping. Fitting through the stretched exponential function (SEF) was performed for each separately extracted ${\Delta } {V}_{\text {T}}$ , and the activation energy for each ${\Delta } {V}_{\text {T}}$ was extracted using the inverse Laplace transform method through the extracted ${\Delta } {V}_{\text {T0}}$ , $\tau $ , and $\beta $ . Activation energy by charge trapping and DOS was extracted from NBIS and PBS, respectively. As a result of simultaneously considering the two degradation mechanisms, the extracted activation energy was located between the previous values. Experimentally extracted sets of DOS-specific parameters before and after bias stress were applied to technology computer-aided design (TCAD) simulations. Accurate reproduction of TFT current–voltage ( ${I}$ – ${V}$ ) curves before and after bias stress and recovery suggests that the methodology and parameter set used in this study are reasonable and potentially useful for a more robust and systematic analysis of the bias stress-induced instability in a-IGZO BG TFTs.