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      Two-terminal floating-gate memory with van der Waals heterostructures for ultrahigh on/off ratio

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          Abstract

          Concepts of non-volatile memory to replace conventional flash memory have suffered from low material reliability and high off-state current, and the use of a thick, rigid blocking oxide layer in flash memory further restricts vertical scale-up. Here, we report a two-terminal floating gate memory, tunnelling random access memory fabricated by a monolayer MoS 2/h-BN/monolayer graphene vertical stack. Our device uses a two-terminal electrode for current flow in the MoS 2 channel and simultaneously for charging and discharging the graphene floating gate through the h-BN tunnelling barrier. By effective charge tunnelling through crystalline h-BN layer and storing charges in graphene layer, our memory device demonstrates an ultimately low off-state current of 10 −14 A, leading to ultrahigh on/off ratio over 10 9, about ∼10 3 times higher than other two-terminal memories. Furthermore, the absence of thick, rigid blocking oxides enables high stretchability (>19%) which is useful for soft electronics.

          Abstract

          Traditional non-volatile memories suffer from poor scalability in the vertical direction due to the use of a bulky oxide layer. Here, the authors develop a tunnelling random access memory using a vertical heterostructure composed of atomically thin molybdenum disulfide, boron nitride and graphene.

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          Most cited references20

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          Van der Waals heterostructures

          Research on graphene and other two-dimensional atomic crystals is intense and likely to remain one of the hottest topics in condensed matter physics and materials science for many years. Looking beyond this field, isolated atomic planes can also be reassembled into designer heterostructures made layer by layer in a precisely chosen sequence. The first - already remarkably complex - such heterostructures (referred to as 'van der Waals') have recently been fabricated and investigated revealing unusual properties and new phenomena. Here we review this emerging research area and attempt to identify future directions. With steady improvement in fabrication techniques, van der Waals heterostructures promise a new gold rush, rather than a graphene aftershock.
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            Boron nitride substrates for high-quality graphene electronics

            Graphene devices on standard SiO2 substrates are highly disordered, exhibiting characteristics far inferior to the expected intrinsic properties of graphene[1-12]. While suspending graphene above the substrate yields substantial improvement in device quality[13,14], this geometry imposes severe limitations on device architecture and functionality. Realization of suspended-like sample quality in a substrate supported geometry is essential to the future progress of graphene technology. In this Letter, we report the fabrication and characterization of high quality exfoliated mono- and bilayer graphene (MLG and BLG) devices on single crystal hexagonal boron nitride (h-BN) substrates, by a mechanical transfer process. Variable-temperature magnetotransport measurements demonstrate that graphene devices on h-BN exhibit enhanced mobility, reduced carrier inhomogeneity, and reduced intrinsic doping in comparison with SiO2-supported devices. The ability to assemble crystalline layered materials in a controlled way sets the stage for new advancements in graphene electronics and enables realization of more complex graphene heterostructres.
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              Phase-change materials for rewriteable data storage.

              Phase-change materials are some of the most promising materials for data-storage applications. They are already used in rewriteable optical data storage and offer great potential as an emerging non-volatile electronic memory. This review looks at the unique property combination that characterizes phase-change materials. The crystalline state often shows an octahedral-like atomic arrangement, frequently accompanied by pronounced lattice distortions and huge vacancy concentrations. This can be attributed to the chemical bonding in phase-change alloys, which is promoted by p-orbitals. From this insight, phase-change alloys with desired properties can be designed. This is demonstrated for the optical properties of phase-change alloys, in particular the contrast between the amorphous and crystalline states. The origin of the fast crystallization kinetics is also discussed.
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                Author and article information

                Journal
                Nat Commun
                Nat Commun
                Nature Communications
                Nature Publishing Group
                2041-1723
                02 September 2016
                2016
                : 7
                : 12725
                Affiliations
                [1 ]Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS) , Suwon 16419, Republic of Korea
                [2 ]Department of Energy Science, Sungkyunkwan University , Suwon 16419, Republic of Korea
                [3 ]Department of Electronic and Electrical Engineering, Sungkyunkwan University , Suwon 16419, Republic of Korea
                [4 ]Samsung Advanced Institute of Technology , Suwon 16678, Republic of Korea
                [5 ]Samsung-SKKU Graphene Center (SSGC), Sungkyunkwan University , Suwon 16419, Republic of Korea
                Author notes
                Author information
                http://orcid.org/0000-0001-7403-8157
                Article
                ncomms12725
                10.1038/ncomms12725
                5025799
                27586841
                47b4847b-da6c-4eca-91d4-5481519f6d40
                Copyright © 2016, The Author(s)

                This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

                History
                : 19 February 2016
                : 27 July 2016
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