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1. Vibrational fingerprints of ferroelectric HfO2

   https://doi.org/10.1038/s41535-022-00436-8  

   Fan, Shiyu; Singh, Sobhit; Xu, Xianghan; Park, Kiman; Qi, Yubo; Cheong, S. W.; Vanderbilt, David; Rabe, Karin M.; Musfeldt, J. L. (December 2022, npj Quantum Materials)

   Abstract Hafnia (HfO 2 ) is a promising material for emerging chip applications due to its high- κ dielectric behavior, suitability for negative capacitance heterostructures, scalable ferroelectricity, and silicon compatibility. The lattice dynamics along with phononic properties such as thermal conductivity, contraction, and heat capacity are under-explored, primarily due to the absence of high quality single crystals. Herein, we report the vibrational properties of a series of HfO 2 crystals stabilized with yttrium (chemical formula HfO 2 :  x Y, where x  = 20, 12, 11, 8, and 0%) and compare our findings with a symmetry analysis and lattice dynamics calculations. We untangle the effects of Y by testing our calculations against the measured Raman and infrared spectra of the cubic, antipolar orthorhombic, and monoclinic phases and then proceed to reveal the signature modes of polar orthorhombic hafnia. This work provides a spectroscopic fingerprint for several different phases of HfO 2 and paves the way for an analysis of mode contributions to high- κ dielectric and ferroelectric properties for chip technologies. 

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2. Intrinsic ferroelectricity in Y-doped HfO2 thin films

   https://doi.org/10.1038/s41563-022-01282-6  

   Yun, Yu; Buragohain, Pratyush; Li, Ming; Ahmadi, Zahra; Zhang, Yizhi; Li, Xin; Wang, Haohan; Li, Jing; Lu, Ping; Tao, Lingling; et al (August 2022, Nature Materials)
3. A Reliability Study of Thickness Dependence of HfO2-based 3D-FeRAM Cell

   Maher, Olivier; Jiang, Hao; Liu, Zhan; and Ma, T.P. (December 2020, IEEE Semiconductor Interface Specialist Conference)

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   Thickness-dependent reliability in 3D-Cap HfO2-based FeRAM capacitors has been studied. Results show endurance larger than 1011 cycles and >10 years of extrapolated retention time. A significant polarization gain was made possible due to trenched capacitors that enhanced the effective areas. A major cause of the endurance failure is the dielectric breakdown after numerous cycles, which is linked to the gate leakage currents. Our temperature-dependent study of I-V characteristics has revealed Fowler-Nordheim tunneling at low temperatures and Frenkel-Poole conduction at room-to-high temperatures as the culprits. Such findings will be helpful for future commercialization of this technology. 

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4. Combined computational and experimental investigation of high temperature thermodynamics and structure of cubic ZrO2 and HfO2

   https://doi.org/10.1038/s41598-018-32848-7  

   Hong, Qi-Jun; Ushakov, Sergey V.; Kapush, Denys; Benmore, Chris J.; Weber, Richard J. K.; van de Walle, Axel; Navrotsky, Alexandra (October 2018, Scientific Reports)

   Abstract Structure and thermodynamics of pure cubic ZrO₂and HfO₂were studied computationally and experimentally from their tetragonal to cubic transition temperatures (2311 and 2530 °C) to their melting points (2710 and 2800 °C). Computations were performed using automatedab initiomolecular dynamics techniques. High temperature synchrotron X-ray diffraction on laser heated aerodynamically levitated samples provided experimental data on volume change during tetragonal-to-cubic phase transformation (0.55 ± 0.09% for ZrO₂and 0.87 ± 0.08% for HfO₂), density and thermal expansion. Fusion enthalpies were measured using drop and catch calorimetry on laser heated levitated samples as 55 ± 7 kJ/mol for ZrO₂and 61 ± 10 kJ/mol for HfO₂, compared with 54 ± 2 and 52 ± 2 kJ/mol from computation. Volumetric thermal expansion for cubic ZrO₂and HfO₂are similar and reach (4 ± 1)·10⁻⁵/K from experiment and (5 ± 1)·10⁻⁵/K from computation. An agreement with experiment renders confidence in values obtained exclusively from computation: namely heat capacity of cubic HfO₂and ZrO₂, volume change on melting, and thermal expansion of the liquid to 3127 °C. Computed oxygen diffusion coefficients indicate that above 2400 °C pure ZrO₂is an excellent oxygen conductor, perhaps even better than YSZ. 

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5. Tuning the electrical performance of solution-processed In2O3TFTs by low-temperature with HfO2-PVP hybrid dielectric

   https://doi.org/10.1016/j.mtcomm.2021.102120  

   Rao, M.G. Syamala; Meza-Arroyo, J.; Reddy, K. Chandra; Murthy, Lakshmi N.S.; de Urquijo-Ventura, M.S.; Garibay-Martínez, F.; Hsu, Julia W.P; Ramirez-Bon, R. (March 2021, Materials Today Communications)

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