Universal PBTI Relaxation on the Negative VTH Shift in Oxide Semiconductor Transistors and New Insights

In this work, the positive bias temperature instability (PBTI) degradation of ZnO transistors by atomic layer deposition (ALD) is systematically investigated by using an extended measure-stress-measure (eMSM) technique. We observe for the first time the anomalous negative threshold voltage ( ${V} _{\textit {TH}}$ ) shift under PBTI stress, which is frequently observed in oxide semiconductor transistors, can be well described by a universal relaxation model. The permanent component ( ${P}$ ) and recoverable component ( ${R}$ ) are simultaneously extracted, clearly showing that the ${R}$ component is dominated by negative ${V} _{\textit {TH}}$ shift while ${P}$ component is positive. The universality of PBTI relaxation on the negative ${V} _{\textit {TH}}$ shift in oxide semiconductors suggests hydrogen (H) transport may play a key role on understanding PBTI degradation phenomenon in oxide semiconductor devices, and relaxation must be considered for accurate evaluation of lifetime.