In-Depth Investigation of Seed Layer Engineering in Ferroelectric Hf_0.5Zr_0.5O₂ Film: Wakeup-Free Achievement and Reliability Mechanisms

Seed layer engineering in ferroelectric (FE) Hf0.5Zr0.5O2 (HZO) film has been investigated systematically in this work. Among four kinds of seed layers (ZrO2, HfO2, Al2O3, and TiO2), the HZO capacitor with TiO2 seed layer achieves preferable performance (larger Pr, smaller Ec, and nearly wakeup-free). It is considered that the suppression of interfacial defects by seed layers could be a key for wakeup-free achievement. For further understanding, with reliability characterizations and theoretical calculations, it is found that defects (oxygen vacancy V+O) generation at the TiN/HZO interface and their migration into inner film could be dominant reasons for the leakage and Pr degradation in cycling, while V-O(+) at the TiO2/TiN interface can attribute to the imprint effect. Thereby, a novel asymmetric stress field cycling (ASFC) scheme is proposed to suppress Pr fatigue by keeping defects at one-side interface rather than migrating into the inner film.