Tailoring the ferroelectric properties of ZrO_2 ultrathin films by interfacial engineering

摘要

This study demonstrates that the ferroelectric (FE) and antiferroelectric (AFE) properties of ZrO_2 ultrathin films (~12 nm in thickness), prepared by atomic layer deposition (ALD), could be tailored by introducing sub-nanometer interfacial layers between the ZrO_2 thin film and top and bottom Pt electrodes. In terms of polarization switching ability and the remanent polarization value, the ferroelectricity of ZrO_2 ultrathin films was greatly enhanced by HfO_2 interfacial layers (i.e., a Pt/HfO_2/ZrO_2/HfO_2/Pt layered arrangement). While TiO_2 interfacial layers (i.e., a Pt/TiO_2/ZrO_2/TiO_2/Pt layered arrangement) led to a transition from FE to AFE. Based on the grazing incidence, out-of-plane and in-plane X-ray diffraction analyses, it is found that the HfO_2 interfacial layers promoted the formation of the polar, ferroelectric orthorhombic (o) phase with (111)-texture within the ZrO_2 thin film. While the TiO_2 interfacial layers promoted the nonpolar tetragonal (t) phase with (110)-texture. The electric field-induced phase transition from the nonpolar t-phase to the polar o-phase occurred at large electric fields, giving rise to an apparent AFE double-loop hysteresis. The modulation of the FE/AFE properties of the ZrO_2 thin film by the HfO_2 or TiO_2 interfacial layers can be achieved without post-annealing. This is particularly favorable to CMOS process integration. This study shows that interface engineering is a critical and effective approach to tailor the FE/AFE characteristics of simple binary oxides such as ZrO_2, making them relevant for technological applications in the field of nanoelectronics.