Effects of heat treatment and in situ high-temperature X-ray diffraction study on the formation of ferroelectric epitaxial Y-doped HfO₂ film

Abstract

The process of forming the ferroelectric orthorhombic phase was investigated for epitaxial 7% Y-doped (YHO7) films using in situ high-temperature X-ray diffraction. Epitaxial YHO7 films were grown on (111) ITO-coated (111)YSZ substrates by pulsed laser deposition at room temperature and a subsequent heat treatment process. Films deposited at room temperature were crystallized as paraelectric monoclinic phase. The monoclinic phase partially changes to tetragonal phase above 600 °C and perfectly transformed around 950 °C during heating. The change from tetragonal phase to orthorhombic phase was detected at 300 °C, corresponding to the Curie temperature under the cooling process. These results clearly suggest that the tetragonal phase was more stable at 1000 °C for YHO7 films on heating than the other phases, and the formation of this tetragonal phase—the high-temperature paraelectric phase of the ferroelectric orthorhombic phase—is key to the formation of the ferroelectric orthorhombic phase.

Electric‐Field‐Induced Ferroelectricity in 5%Y‐doped Hf0.5Zr0.5O2: Transformation from the Paraelectric Tetragonal Phase to the Ferroelectric Orthorhombic Phase

“…[28,29] The details of the phase assignments can also be found in previous studies. [30,31] No spots are shown in Figure 1b, indicating that the 1100 C-treated film consists of the tetragonal phase because the existence of the other phase should lead to the appearance of the peak. On the other hand, two spots are shown in Figure 1a, which suggests the existence of monoclinic films.…”

“…Previous results on the heat‐treatment temperature dependence of the constituent phases and electric properties in the Y‐doped HfO 2 films show that the orthorhombic phase can be obtained via a higher‐temperature annealing. [ 30 ] In situ XRD measurements indicate the importance of the phase transition from the as‐deposited monoclinic phase to the tetragonal phase during the heat treatment and the transformation of the tetragonal phase to the orthorhombic phase upon cooling. Generally, the phase transition from the monoclinic phase to the tetragonal phase is a first‐order phase transition with large thermal hysteresis in fluorite oxides, such as ZrO 2 and HfO 2 .…”

“…These values are comparable with the previous results for epitaxial Y‐HfO 2 films. [ 30–32 ] The values of saturated polarization are 15 and 21 μC cm −2 for the 1000 and 1100 °C heat‐treated films, respectively. According to the recent DFT calculation, the spontaneous polarization is reported to be about 50–60 μC cm −2 .…”

Effects of growth orientations and epitaxial strains on phase stability of HfO2 thin films

“…This kinetic argument is supported by recent experimental work on the effect of heat treatment on the formation of ferroelectric epitaxial (111)-oriented 7% Y-doped HfO 2 (YHO7) thin films. 57 In this work, the as-deposited YHO7 films were heat-treated by a rapid thermal furnace at various temperatures. It was found that the as-deposited and lower temperature treatment resulted in M phase whereas a higher temperature treatment leads to more O/T phases.…”

Critical effect of the bottom electrode on the ferroelectricity of epitaxial Hf0.5Zr0.5O2thin films

“…5 Epitaxial films are being investigated now very actively. Several conducting or semiconducting substrates or templates, including Si wafers, 6 TiN, 7 GaN, 8 and indium tin oxide, 9 have been used to deposit epitaxial films of ferroelectric doped HfO 2 . In contrast, epitaxy of hafnia on perovskite-type oxide electrodes has only been reported on Nb-doped SrTiO 3 (Nb:STO) 10 and La 0.67 Sr 0.33 MnO 3 (LSMO).…”