Nanoscale phase change memory materials

Caldwell, Marissa A.; Jeyasingh, Rakesh; Wong, H.-S. Philip; Milliron, Delia J.

doi:10.1039/c2nr30541k

Cited by 60 publications

(38 citation statements)

References 60 publications

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“…Reduced heat loss from the PCM layer has been demonstrated recently with carbon nanotubes [25,26] and graphene [27], where low set and reset currents were attained, and 10 5 programming cycles were achieved with graphene as an electrode interface material [27]. The interaction between the PCM and the heater (such as TiN) also leads to degradation of PC-RAM [28,29], which could well be reduced by a graphene buffer between them. A graphene buffer could aid other applications, such as ferroelectricity in PCM [30,31].…”

Section: Introductionmentioning

confidence: 99%

Tuning electronic properties of graphene heterostructures by amorphous-to-crystalline phase transitions

2016

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The remarkable ability of phase change materials (PCM) to switch between amorphous and crystalline states on a nanosecond time scale could provide new opportunities for graphene engineering. We have used density functional calculations to investigate the structures and electronic properties of heterostructures of thin amorphous and crystalline films of the PCM GeTe (16Å thick) and Ge2Sb2Te5 (20Å) between graphene layers. The interaction between graphene and PCM is very weak, charge transfer is negligible, and the structures of the chalcogenide films differ little from those of bulk phases. A crystalline GeTe (111) layer induces a band gap opening of 80 meV at the Dirac point. This effect is absent for the amorphous film, but the Fermi energy shifts down along the Dirac cone by −60 meV. Ge2Sb2Te5 shows similar features, although inherent disorder in the crystalline rocksalt structure reduces the contrast in band structure from that in the amorphous structure. These features originate in charge polarization within the crystalline films, which show electromechanical response (piezoelectricity) upon compression, and show that the electronic properties of graphene structures can be tuned by inducing ultra-fast structural transitions within the chalcogenide layers. Graphene can also be used to manipulate the structural state of the PCM layer and its electronic and optical properties.

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Section: Introductionmentioning

confidence: 99%

Tuning electronic properties of graphene heterostructures by amorphous-to-crystalline phase transitions

2016

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“…Phase-Change materials (PCMs) possess a unique property portfolio, which is ideally suited for memory device applications123456. A PCM is identified by its ability of switching rapidly and reversibly between a crystalline and an amorphous state, where the amorphous state is obtained by melting the crystalline state followed by rapid quenching.…”

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confidence: 99%

Revisiting the Local Structure in Ge-Sb-Te based Chalcogenide Superlattices

Casarin

Caretta

Momand

et al. 2016

Sci Rep

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The technological success of phase-change materials in the field of data storage and functional systems stems from their distinctive electronic and structural peculiarities on the nanoscale. Recently, superlattice structures have been demonstrated to dramatically improve the optical and electrical performances of these chalcogenide based phase-change materials. In this perspective, unravelling the atomistic structure that originates the improvements in switching time and switching energy is paramount in order to design nanoscale structures with even enhanced functional properties. This study reveals a high-resolution atomistic insight of the [GeTe/Sb 2 Te 3 ] interfacial structure by means of Extended X-Ray Absorption Fine Structure spectroscopy and Transmission Electron Microscopy. Based on our results we propose a consistent novel structure for this kind of chalcogenide superlattices.The need for fast and efficient management of information stimulates research on materials that can be switched on nanometer length scales and sub-nanosecond time scales. Phase-Change materials (PCMs) possess a unique property portfolio, which is ideally suited for memory device applications [1][2][3][4][5][6] . A PCM is identified by its ability of switching rapidly and reversibly between a crystalline and an amorphous state, where the amorphous state is obtained by melting the crystalline state followed by rapid quenching. These two states significantly differ in their properties, such as the optical reflectivity as well as the electrical conductivity. The phase transformation is in general triggered by thermal heating, or by either electrical and optical pulses of different time duration and amplitude. The large contrast in reflectivity between these two states lays at the base of already working PCM-based optical rewritable media devices-like DVDs or Blu-Ray Disc-where information is encoded as amorphous marks in a crystalline background. The contrast in resistivity could be exploited in the next generation of electronic solid-state memories based on PCMs, which might replace the current leading storage technologies, namely FLASH and magnetic disks. Furthermore, these materials could be employed in displays or data visualization applications by combining both their optical and electronic property modulations 7 . Hence, a lot of interest and effort is currently devoted to uncover the complex physical origin of the high contrast between the two phases [8][9][10]

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“…Compared to top-down processing, bottom-up techniques provide remarkably better control in size and shape of the materials18. Although solution based synthesis can produce extraordinary GeTe NPs, it remains highly challenging to synthesize other PCMs NPs, such as binary GeSb or even more complicated ternary (pseudo-binary) GeSbTe systems18.…”

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confidence: 99%

“…Although solution based synthesis can produce extraordinary GeTe NPs, it remains highly challenging to synthesize other PCMs NPs, such as binary GeSb or even more complicated ternary (pseudo-binary) GeSbTe systems18. Laser ablation is another alternative that has been explored to produce GST NPs, yet inconsistent but exceptional results have been reported on the crystallization of GST NPs.…”

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confidence: 99%

Size-dependent and tunable crystallization of GeSbTe phase-change nanoparticles

Chen

Brink

Palasantzas

et al. 2016

Sci Rep

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Chalcogenide-based nanostructured phase-change materials (PCMs) are considered promising building blocks for non-volatile memory due to their high write and read speeds, high data-storage density, and low power consumption. Top-down fabrication of PCM nanoparticles (NPs), however, often results in damage and deterioration of their useful properties. Gas-phase condensation based on magnetron sputtering offers an attractive and straightforward solution to continuously down-scale the PCMs into sub-lithographic sizes. Here we unprecedentedly present the size dependence of crystallization for Ge2Sb2Te5 (GST) NPs, whose production is currently highly challenging for chemical synthesis or top-down fabrication. Both amorphous and crystalline NPs have been produced with excellent size and composition control with average diameters varying between 8 and 17 nm. The size-dependent crystallization of these NPs was carefully analyzed through in-situ heating in a transmission electron microscope, where the crystallization temperatures (Tc) decrease when the NPs become smaller. Moreover, methane incorporation has been observed as an effective method to enhance the amorphous phase stability of the NPs. This work therefore elucidates that GST NPs synthesized by gas-phase condensation with tailored properties are promising alternatives in designing phase-change memories constrained by optical lithography limitations.

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Nanoscale phase change memory materials

Cited by 60 publications

References 60 publications

Tuning electronic properties of graphene heterostructures by amorphous-to-crystalline phase transitions

Tuning electronic properties of graphene heterostructures by amorphous-to-crystalline phase transitions

Revisiting the Local Structure in Ge-Sb-Te based Chalcogenide Superlattices

Size-dependent and tunable crystallization of GeSbTe phase-change nanoparticles

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