Interfacial Layer Engineering in Zr-Doped HfO ₂ Ferroelectric Films: Trade-Off Between Polarization Enhancement and Reliability

HfO₂-based ferroelectric materials have attracted significant attention for next-generation nonvolatile memory applications due to their superior ferroelectric properties and CMOS compatibility. In this study, <i>Zr</i>-doped HfO₂ (HZO) films with various engineered interfacial layers [Al₂O₃ (<i>Al</i>-HZO), HfO₂ (<i>Hf</i>-HZO), and ZrO₂ (<i>Zr</i>-HZO)] were systematically investigated. Compared with the control device without an interfacial layer, the incorporation of interfacial layers effectively suppresses the interface trap density (<i>D</i>_it), thereby enhancing the polarization performance. Notably, the <i>Al</i>-HZO exhibits the strongest suppression of interfacial defects due to pronounced interfacial dipole effects, but it also induces a larger depolarization field, resulting in a slight reduction in remanent polarization. In contrast, both <i>Zr</i>-HZO and <i>Hf</i>-HZO interfacial layers enhance polarization, with HfO₂ delivering the most significant improvement, which is attributed to an increased proportion of the orthorhombic (o) phase within the HZO films. Moreover, a detailed analysis of polarization loss (<i>P</i>_loss) under varying electric field amplitudes (<i>E</i>_A) reveals a positive correlation between the depolarization field and polarization strength; i.e., stronger polarization corresponds to a larger depolarization field. Among all samples, <i>Al</i>-HZO shows the highest <i>P</i>_loss due to interfacial discontinuity, which also leads to early dielectric breakdown under forward constant voltage stress (FCVS). Furthermore, the effect of various interfacial layers on the switching dynamics of HZO films was also examined, revealing that interfacial engineering can significantly improve the polarization switching speed. Among them, <i>Al</i>-HZO exhibits superior local field uniformity, the lowest activation field, and the fastest switching response. These findings provide valuable insights into the complex interfacial effects in HfO₂-based ferroelectric transistors.