Mechanism of amorphous phase stabilization in ultrathin films of monoatomic phase change material

Dragoni, Daniele; Behler, Jörg; Bernasconi, Marco

doi:10.1039/d1nr03432d

Cited by 24 publications

(25 citation statements)

References 56 publications

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“…The lower density layer, instead, could be attributed to a residual amorphous onset layer (a-Sb). This was previously reported for the stabilization of thin (<10 nm) Sb and PC-materials stacked between different electrode materials [ 21 , 22 , 23 , 24 ].…”

Section: Resultssupporting

confidence: 67%

“…In a first approach, the deposition of all layers was performed at an elevated temperature (T = 200 °C), as it has been shown that temperature is a critical parameter to tune the growth of thin PC-materials [ 22 , 23 , 24 , 25 ]. The results of the structural investigation are shown in Figure 2 a and Table 4 .…”

Section: Resultsmentioning

confidence: 99%

“…When designing a PCM cell, downscaling the thickness of the PC-material is known to be an important parameter to tune device metrics, including the resistance window, programming currents and amorphous phase retention [ 16 , 24 , 28 ]. Hence, we investigated the limit case of an ultrathin 3 nm Sb ( Stack D ).…”

Section: Resultsmentioning

confidence: 99%

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Structural Assessment of Interfaces in Projected Phase-Change Memory

et al. 2022

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Non-volatile memories based on phase-change materials have gained ground for applications in analog in-memory computing. Nonetheless, non-idealities inherent to the material result in device resistance variations that impair the achievable numerical precision. Projected-type phase-change memory devices reduce these non-idealities. In a projected phase-change memory, the phase-change storage mechanism is decoupled from the information retrieval process by using projection of the phase-change material’s phase configuration onto a projection liner. It has been suggested that the interface resistance between the phase-change material and the projection liner is an important parameter that dictates the efficacy of the projection. In this work, we establish a metrology framework to assess and understand the relevant the structural properties of the interfaces in thin films contained in projected memory devices. Using X-ray reflectivity, X-ray diffraction and transmission electron microscopy, we investigate the quality of the interfaces and the layers’ properties. Using demonstrator examples of Sb and Sb2Te3 phase-change materials, new deposition routes as well as stack designs are proposed to enhance the phase-change material to a projection-liner interface and the robustness of material stacks in the devices.

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Section: Resultssupporting

confidence: 67%

Section: Resultsmentioning

confidence: 99%

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Structural Assessment of Interfaces in Projected Phase-Change Memory

et al. 2022

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“…However, there is also the effect of increased confinement for thinner films that retards the crystal growth. 11 Note that Sb films show an extremely growth-dominated crystallization behavior. Earlier results on 200 nm thick Sb films (containing 7 atom % Ge) show crystal sizes in the order of millimeters.…”

Section: Results and Discussionmentioning

confidence: 99%

Thickness-Dependent Crystallization of Ultrathin Antimony Thin Films for Monatomic Multilevel Reflectance and Phase Change Memory Designs

Yimam

Kooi

2022

ACS Appl. Mater. Interfaces

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Phase change materials, with more than one reflectance and resistance states, have been a subject of interest in the fields of phase change memories and nanophotonics. Although most current research focuses on rather complex phase change alloys, e.g. , Ge2Sb2Te5, recently, monatomic antimony thin films have aroused a lot of interest. One prominent attractive feature is its simplicity, giving fewer reliability issues like segregation and phase separation. However, phase transformation and crystallization properties of ultrathin Sb thin films must be understood to fully incorporate them into future memory and nanophotonics devices. Here, we studied the thickness-dependent crystallization behavior of pulsed laser-deposited ultrathin Sb thin films by employing dynamic ellipsometry. We show that the crystallization temperature and phase transformation speed of as-deposited amorphous Sb thin films are thickness-dependent and can be precisely tuned by controlling the film thickness. Thus, crystallization temperature tuning by thickness can be applied to future memory and nanophotonic devices. As a proof of principle, we designed a heterostructure device with three Sb layers of varying thicknesses with distinct crystallization temperatures. Measurements and simulation results show that it is possible to address these layers individually and produce distinct and multiple reflectance profiles in a single device. In addition, we show that the immiscible nature of Sb and GaSb could open up possible heterostructure device designs with high stability after melt-quench and increased crystallization temperature. Our results demonstrate that the thickness-dependent phase transformation and crystallization dynamics of ultrathin Sb thin films have attractive features for future memory and nanophotonic devices.

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“…The endothermic peak (277–292 °C) is attributed to the T m of crystalline amylopectin and co-crystallised amylose [ 62 ]. T m is the temperature at which the crystalline region of the polymer turns amorphous; it is the characteristic peak for the crystalline materials [ 63 ]. The T m peaks become smaller as the composition of PANI increases in the matrix.…”

Section: Resultsmentioning

confidence: 99%

Starch/Polyaniline Biopolymer Film as Potential Intelligent Food Packaging with Colourimetric Ammonia Sensor

2022

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The use of petroleum-based plastics in food packaging leads to various environmental impacts, while spoilage of food and misinterpretation of food-date labelling account for food insecurity; therefore, a biopolymer capable of indicating food edibility is prepared to resolve these issues. In this research, starch/polyaniline (starch/PANI) biopolymer film was synthesised and investigated as an ammonia sensor for potential application as intelligent food packaging. FT-IR and XRD were used to confirm the composition of the biopolymer films, while UV-Vis spectrometry was applied to identify the oxidation state of PANI in emeraldine form. PANI was successfully incorporated into the starch matrix, leading to better thermal stability (TGA) but decreasing the crystallinity of the matrix (DSC). The performance of the polymer-film sensor was determined through ammonia-vapour sensitivity analysis. An obvious colour change from green to blue of starch/PANI films was observed upon exposure to the ammonia vapour. Starch/PANI 0.4% is the optimum composition, having the best sensor performance with good linearity (R2 = 0.9459) and precision (RSD = 8.72%), and exhibiting excellent LOD (245 ppm). Furthermore, the starch/PANI films are only selective to ammonia. Therefore, the starch/PANI films can be potentially applied as colourimetric ammonia sensors for intelligent food packaging.

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Mechanism of amorphous phase stabilization in ultrathin films of monoatomic phase change material

Abstract: Large scale atomistic simulations with an interatomic potential generated by a machine learning method have been exploited to study the crystallization of Sb in ultrathin films.

Cited by 24 publications

References 56 publications

Structural Assessment of Interfaces in Projected Phase-Change Memory

Structural Assessment of Interfaces in Projected Phase-Change Memory

Thickness-Dependent Crystallization of Ultrathin Antimony Thin Films for Monatomic Multilevel Reflectance and Phase Change Memory Designs

Starch/Polyaniline Biopolymer Film as Potential Intelligent Food Packaging with Colourimetric Ammonia Sensor

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