Understanding and modelling the PBTI reliability of thin-film IGZO transistors

We study the impact of the gate-dielectric on the Positive Bias Temperature Instability (PBTI) of IGZO thin-film transistors (TFT). We show that PBTI is controlled by the gate-dielectric pre-existent electron traps and its hydrogen content. The degradation process can be composed of up to four different mechanisms with different time kinetics, voltage acceleration factors and activation energies. A simplified physics-based model is used to reproduce stress and relaxation traces recorded in a wide range of test conditions. Gate-dielectric optimization enables scaled EOT (2.5nm) IGZO TFT to achieve a record lifetime of ~ 1 year continuous operation at 95°C and $\mathrm{V}_{\text{ov}}=1\mathrm{V}$ , with a strict failure criterion of $\vert \Delta \mathrm{V}_{\text{th}}\vert < 30\text{mV}$ .