Robustness of Ferroelectricity in Hafnium-Zirconium Dioxide Films Deposited By Sputtering and Chemical Solution Deposition for Ferroelectric Transistor Applications

Abstract

Since the discovery of ferroelectricity in HfO2 in 2011, extensive work begin to burst forth on HfO2-based ferroelectric materials and devices. Orthorhombic phase is responsible for ferroelectricity in HfO2, which is usually stabilized by the dopant such as Al, Zr, Si, la and Y. In particular, Zr doped HfO2 (HZO) has large Pr around 20 µC/cm2 and ferroelectricity can be obtained in a wide range of Zr composition. The orthorhombic phase is a metastable phase and Migita et al. [1] reported that the orthorhombic phase of sputtered HZO film was transferred to monoclinic phase by further annealing. In this work, robustness of ferroelectric phase against the further annealing process has been investigated using sputtered HZO and solution-derived Y-doped HZO films [2].Sputtered HZO films were prepared by room temperature deposition followed by 600 oC, 10 min annealing in N2. Y-doped HZO films were prepared by chemical solution deposition (CSD) by annealing the samples at 800 oC for 3 min in O2.[2] Ferroelectric properties were confirmed by polarization-electric field (P-E) and capacitance-voltage (C-V) measurements for both samples before the second time annealing. Then, both samples were further annealed in 400 and 600 oC in N2 to examine the robustness of ferroelectricity. It was found that sputtered HZO films become paraelectric and that X-ray diffraction (XRD) pattern shows diffraction peak from orthorhombic phase disappeared. On the other hand, CSD HZO films shows ferroelectric nature even after second time annealing with negligible monoclinic phase. Such a significant difference in robustness is presumably due to residual carbon in the CSD films.In addition, In2O3/(Y-)HZO structures are also fabricated for oxide channel thin film transistor applications and characterized, which will be presented at the conference.[1] Shinji Migita et al, Jpn. J. Appl. Phys. 58 SBBA07, 2019.[2] Mohit et al, Jpn. J. Appl. Phys. 59 SMMB02, 2020.