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 (ΔV_T) caused by different oxygen flow rates (OFR) and various V_GS and V_DS combinations was measured and analyzed. In addition, the CS-induced ΔV_T 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 (E_A) 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 ΔV_T model of IGZO TFT under CS should be helpful in the design of instability-aware circuits.