Nanocrystallite Seeding of Metastable Ferroelectric Phase Formation in Atomic Layer-Deposited Hafnia–Zirconia Alloys

• Published in: ACS applied materials & interfaces Vol. 14; no. 47; pp. 53057 - 53064
• Main Authors: Yu, Zhouchangwan, Saini, Balreen, Liu, Yunzhi, Huang, Fei, Mehta, Apurva, Baniecki, John D., Wong, H.-S. Philip, Tsai, Wilman, McIntyre, Paul C.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 30.11.2022
• Subjects: Functional Inorganic Materials and Devices; ferroelectric; hafnium oxide; phase transition; zirconium oxide; nanocrystallite
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.2c15047

Hafnia-based ferroelectric thin films are promising for semiconductor memory and neuromorphic computing applications. Amorphous, as-deposited, thin-film binary alloys of HfO2 and ZrO2 transform to the metastable, orthorhombic ferroelectric phase during post-deposition annealing and cooling. This transformation is generally thought to involve formation of a tetragonal precursor phase that distorts into the orthorhombic phase during cooling. In this work, we systematically study the effects of atomic layer deposition (ALD) temperature on the ferroelectricity of post-deposition-annealed Hf0.5Zr0.5O2 (HZO) thin films. Seed crystallites having interplanar spacings consistent with the polar orthorhombic phase are observed by a plan-view transmission electron microscope in HZO thin films deposited at an elevated ALD temperature. After ALD under conditions that promote formation of these nanocrystallites, high-polarization (P r > 18 μC/cm2) ferroelectric switching is observed after rapid thermal annealing (RTA) at low temperature (350 °C). These results indicate the presence of minimal non-ferroelectric phases retained in the films after RTA when the ALD process forms nanocrystalline particles that seed subsequent formation of the polar orthorhombic phase.