Physical model of a local threshold voltage shift in InGaZnO thin-film transistors under current stress for instability-aware circuit design

In this study, the degradation mechanism of bottom-gate InGaZnO thin-film transistors (IGZO TFTs) under current stress (CS) was analyzed. The threshold voltage shift (ΔVT) caused by different oxygen flow rates (OFR) and various VGS and VDS combinations was measured and analyzed. In addition, the CS-induced ΔVT was modeled and quantified using the parameters of the multiple stretched exponential functions (MSEF). The quantitative parameters for the lateral field-induced degradation mechanisms were analyzed for each source and drain region. Also, the activation energy (EA) for each mechanism was extracted, and it was confirmed that the donor creation near the drain was caused by oxygen vacancy ionization. Finally, the parameters of subgap density-of-states were extracted using the monochromatic photonic capacitance-voltage (MPCV) method. The proposed physical ΔVT model of IGZO TFT under CS should be helpful in the design of instability-aware circuits.