Liu Kai, Jin Feng, Zhou Luyao, Liu Kuan, Fang Jie, Lu Jingdi, Ma Chao, Wang Lingfei, Wu Wenbin
Hefei National Research Center for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, China.
College of Materials Science and Engineering, Hunan University, Changsha 410082, China.
ACS Appl Mater Interfaces. 2024 Nov 6;16(44):61239-61248. doi: 10.1021/acsami.4c10853. Epub 2024 Oct 23.
Hafnium-based binary oxides are essential for fabricating nanoscale high-density ferroelectric memory devices. However, effective strategies to control and improve their thin-film single crystallinity and metastable ferroelectricity remain elusive, hindering potential applications. Here, using NdGaO (NGO) substrates with four crystalline orientations, we report a systematic study of the structural characterizations and ferroelectric properties of epitaxial HfZrO (HZO) films, demonstrating orientation-controlled high crystallinity and enhanced ferroelectric properties. HZO films grown on NGO(001) and NGO(110) substrates exhibit relatively low crystallinity and a significant presence of the monoclinic phase. In contrast, HZO films grown on NGO(100) and NGO(010) possess high single crystallinity and a dominant ferroelectric phase. These differences are attributed to the surface symmetry of the NGO substrate, which favors the formation of 4- or 2-fold domain configurations. Moreover, the optimized HZO films exhibit a large polarization (2) of ∼50 μC/cm, enhanced fatigue behavior up to 10 cycles, improved retention of 2 ∼ 40 μC/cm after 10 years, and characteristic polarization switching speeds in the submicrosecond range. Our results highlight the importance of modulating the single crystallinity and ferroelectric phase fraction of HfO-based films to enhance ferroelectric properties, further revealing the potential of epitaxial symmetry engineering.
基于铪的二元氧化物对于制造纳米级高密度铁电存储器件至关重要。然而，控制和改善其薄膜单晶性和亚稳铁电性的有效策略仍然难以捉摸，这阻碍了其潜在应用。在此，我们使用具有四种晶体取向的钕镓酸盐（NdGaO，NGO）衬底，对外延生长的铪锆氧化物（HfZrO，HZO）薄膜的结构特征和铁电性能进行了系统研究，证明了通过取向控制可实现高结晶度和增强的铁电性能。在NGO(001)和NGO(110)衬底上生长的HZO薄膜结晶度相对较低，且存在大量单斜相。相比之下，在NGO(100)和NGO(010)上生长的HZO薄膜具有高单晶性和主导的铁电相。这些差异归因于NGO衬底的表面对称性，其有利于形成四重或二重畴结构。此外，优化后的HZO薄膜表现出约50 μC/cm²的大极化强度、高达10⁹次循环的增强抗疲劳性能、10年后约2-40 μC/cm²的改善的极化保持率以及亚微秒范围内的特征极化切换速度。我们的结果突出了调节基于HfO薄膜的单晶性和铁电相分数以增强铁电性能的重要性，进一步揭示了外延对称性工程的潜力。
