Enhancing FeFET Memory Reliability via Switching Mechanism Control by Compositionally Gradient-Stacked Hf1-xZrxO2 Films

Hf1-xZrxO2 (HZO)-based n-channel FeFETs utilizing a compositionally gradient-stacked ferroelectric (FE) layer were employed as a platform to explore the switching mechanism and the reliability of device performance. Compared to FeFETs with uniform-composition HZO, although those with compositionally gradient-stacked HZO demonstrate a similar memory window (MW), the dipole switching mechanism transitions from the nucleation-limited switching (NLS) model to the Kolmogorov-Avrami-Ishibashi (KAI) model. This transformation enhances switching speed due to the reduced number of domain walls. For FeFETs with gradient-stacked HZO, those with Zr-rich bottom layers show superior endurance compared to Hf-rich counterparts due to the reduced amount of oxygen vacancies, and exhibit promising performance with a 2.2 V MW under ±5 V/ $2~\mu $ s operation while maintaining 91 % of the MW after 107 cycles.