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1. Reduced fatigue and leakage of ferroelectric TiN/Hf _0.5 Zr _0.5 O ₂ /TiN capacitors by thin alumina interlayers at the top or bottom interface

   https://doi.org/10.1088/1361-6528/acad0a  

   Hsain, H Alex; Lee, Younghwan; Lancaster, Suzanne; Lomenzo, Patrick D; Xu, Bohan; Mikolajick, Thomas; Schroeder, Uwe; Parsons, Gregory N; Jones, Jacob L (January 2023, Nanotechnology)

   Abstract Hf 0.5 Zr 0.5 O 2 (HZO) thin films are promising candidates for non-volatile memory and other related applications due to their demonstrated ferroelectricity at the nanoscale and compatibility with Si processing. However, one reason that HZO has not been fully scaled into industrial applications is due to its deleterious wake-up and fatigue behavior which leads to an inconsistent remanent polarization during cycling. In this study, we explore an interfacial engineering strategy in which we insert 1 nm Al 2 O 3 interlayers at either the top or bottom HZO/TiN interface of sequentially deposited metal-ferroelectric-metal capacitors. By inserting an interfacial layer while limiting exposure to the ambient environment, we successfully introduce a protective passivating layer of Al 2 O 3 that provides excess oxygen to mitigate vacancy formation at the interface. We report that TiN/HZO/TiN capacitors with a 1 nm Al 2 O 3 at the top interface demonstrate a higher remanent polarization (2P r ∼ 42 μ C cm −2 ) and endurance limit beyond 10 8 cycles at a cycling field amplitude of 3.5 MV cm −1 . We use time-of-flight secondary ion mass spectrometry, energy dispersive spectroscopy, and grazing incidence x-ray diffraction to elucidate the origin of enhanced endurance and leakage properties in capacitors with an inserted 1 nm Al 2 O 3 layer. We demonstrate that the use of Al 2 O 3 as a passivating dielectric, coupled with sequential ALD fabrication, is an effective means of interfacial engineering and enhances the performance of ferroelectric HZO devices. 

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2. Large remnant polarization and great reliability characteristics in W/HZO/W ferroelectric capacitors

   https://doi.org/10.3389/fmats.2022.969188  

   Asapu, Shiva; Pagaduan, James Nicolas; Zhuo, Ye; Moon, Taehwan; Midya, Rivu; Gao, Dawei; Lee, Jungmin; Wu, Qing; Barnell, Mark; Ganguli, Sabyasachi; et al (August 2022, Frontiers in Materials)

   In this work, the effect of rapid thermal annealing (RTA) temperature on the ferroelectric polarization in zirconium-doped hafnium oxide (HZO) was studied. To maximize remnant polarization (2P r ), in-plane tensile stress was induced by tungsten electrodes under optimal RTA temperatures. We observed an increase in 2P r with RTA temperature, likely due to an increased proportion of the polar ferroelectric phase in HZO. The HZO capacitors annealed at 400°C did not exhibit any ferroelectric behavior, whereas the HZO capacitors annealed at 800°C became highly leaky and shorted for voltages above 1 V. On the other hand, annealing at 700 °C produced HZO capacitors with a record-high 2P r of ∼ 64 μ C cm −2  at a relatively high frequency of 111 kHz. These ferroelectric capacitors have also demonstrated impressive endurance and retention characteristics, which will greatly benefit neuromorphic computing applications. 

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3. Impact of Electric Field Pulse Duration on Ferroelectric Hafnium Zirconium Oxide Thin Film Capacitor Endurance

   https://doi.org/10.1002/pssa.202300566  

   Lenox, Megan K.; Jaszewski, Samantha T.; Fields, Shelby S.; Shukla, Nikhil; Ihlefeld, Jon F. (November 2023, physica status solidi (a))

   While ferroelectric HfO₂shows promise for use in memory technologies, limited endurance is one factor that challenges its widespread application. Herein, endurance is investigated through field cycling W/Hf_0.5Zr_0.5O₂/W capacitors above the coercive field while manipulating the time under field using bipolar pulses of varying pulse duration or duty cycle. Both remanent polarization and leakage current increase with increasing pulse duration. Additionally, an order of magnitude decrease in the pulse duration from 20 to 2 μs results in an increase in endurance lifetime of nearly two orders of magnitude from 3 × 10⁶to 2 × 10⁸cycles. These behaviors are attributed to increasing time under field allowing for charged oxygen vacancy migration, initially unpinning domains, or driving phase transformations before segregating to grain boundaries and electrode interfaces. This oxygen vacancy migration causes increasing polarization before creating conducting percolation paths that result in degradation and premature device failure. This process is suppressed for 2 μs pulse duration field cycling where minimal wake‐up and lower leakage before device failure are observed, suggesting that very short pulses can be used to significantly increase device endurance. These results provide insight into the impact of pulse duration on device performance and highlight consideration of use of conditions when endurance testing. 

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4. Enhanced Ionic/Electronic Transport in Nano‐TiO ₂ /Sheared CNT Composite Electrode for Na ⁺ Insertion‐based Hybrid Ion‐Capacitors

   https://doi.org/10.1002/adfm.201908309  

   Luo, Sainan; Yuan, Tao; Soule, Luke; Ruan, Jiafeng; Zhao, Yahui; Sun, Dalin; Yang, Junhe; Liu, Meilin; Zheng, Shiyou (November 2019, Advanced Functional Materials)

   Abstract Ion‐insertion capacitors show promise to bridge the gap between supercapacitors of high power densities and batteries of high energy densities. While research efforts have primarily focused on Li⁺‐based capacitors (LICs), Na⁺‐based capacitors (SICs) are theoretically cheaper and more sustainable. Owing to the larger size of Na⁺compared to Li⁺, finding high‐rate anode materials for SICs has been challenging. Herein, an SIC anode architecture is reported consisting of TiO₂nanoparticles anchored on a sheared‐carbon nanotubes backbone (TiO₂/SCNT). The SCNT architecture provides advantages over other carbon architectures commonly used, such as reduced graphene oxide and CNT. In a half‐cell, the TiO₂/SCNT electrode shows a capacity of 267 mAh g⁻¹at a 1 C charge/discharge rate and a capacity of 136 mAh g⁻¹at 10 C while maintaining 87% of initial capacity over 1000 cycles. When combined with activated carbon (AC) in a full cell, an energy density and power density of 54.9 Wh kg⁻¹and 1410 W kg⁻¹, respectively, are achieved while retaining a 90% capacity retention over 5000 cycles. The favorable rate capability, energy and power density, and durability of the electrode is attributed to the enhanced electronic and Na⁺conductivity of the TiO₂/SCNT architecture. 

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5. Invasive Cuban Treefrogs (Osteopilus septentrionalis) Have More Robust Locomotor Performance Than Two Native Treefrogs (Hyla spp.) in Florida, USA, in Response to Temperature and Parasitic Infections

   https://doi.org/10.3390/d13030109  

   Roznik, Elizabeth A.; Cano, Natalia; Surbaugh, Kerri L.; Ramsay, Chloe T.; Rohr, Jason R. (March 2021, Diversity)

   null (Ed.)

   Introduced species pose a threat to biodiversity, and ecological and physiological factors are important in determining whether an introduced species becomes successfully established in a new region. Locomotor performance is one such factor that can influence the abundance and distribution of an introduced species. We investigated the effects of temperature and parasitism by the intestinal nematode Aplectana hamatospicula on the maximum jump distance and endurance in one invasive and two native treefrogs in Florida, USA. We collected frogs from the wild, estimated their parasite loads, and tested their locomotor performance at three temperatures. Contrary to expectations, invasive Cuban treefrogs (Osteopilus septentrionalis), which are adapted to a warmer climate in the Caribbean, outperformed pinewoods treefrogs (Hyla femoralis) and squirrel treefrogs (H. squirella) at each temperature, even when controlling for body size differences. In all three species, maximum jump distance was positively related to temperature, and this relationship was stronger for larger frogs. Parasites influenced both the maximum jump distance and endurance of frogs. In all three species, larger frogs jumped farther maximum distances than smaller frogs, but this relationship was stronger when frogs had lower, rather than higher, parasite loads. Parasitism had little effect on endurance in invasive frogs, but it tended to decrease the endurance of native frogs at high temperatures. Furthermore, at low temperatures, the lengths of consecutive jumps of infected native frogs tended to increase, suggesting that parasites limited the distances of initial jumps. Effects of temperature and parasites on the locomotor performance of frogs could influence their abilities to forage, escape predators, and disperse. The tremendous locomotor performance of O. septentrionalis, which is maintained across temperatures and parasite loads, likely contributes to the invasion success of this species. 

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