The refractive index of commercial chalcogenide glasses (ChGs) available in the market is generally 2.4 to 2.7, which is relatively low and has huge room for improvement. In this paper, different ratios of Ag/Pb were doped into commercial glasses by the melt-quenching method to substantially increase their refractive index. The refractive index of the commercial Ge28Sb12Se60 glass was increased from 2.6 to 3.05 by external doping with 20 atomic percentage (at%) of Ag. And the refractive index of commercially available Ge33As12Se55 glass was increased from 2.45 to 2.88 by external doping with 9 at% of Pb. These improvements effectively reduce the thickness of commercial lenses at the same radius of curvature and focal length. The physical and optical properties of commercial glasses doped with Ag/Pb in different proportions were systematically characterized.
With the growing need for extensive data storage, enhancing the storage density of nonvolatile memory technologies presents a significant challenge for commercial applications. This study explores the use of monatomic antimony (Sb) in multi-level phase-change storage, leveraging its thickness-dependent crystallization behavior. We optimized nanoscale Sb films capped with a 4-nm SiO2 layer, which exhibit excellent amorphous thermal stability. The crystallization temperature ranges from 165 to 245 °C as the film thickness decreases from 5 to 3 nm. These optimized films were then assembled into a multilayer structure to achieve multi-level phase-change storage. A typical multilayer film consisting of three Sb layers was fabricated as phase-change random access memory (PCRAM), demonstrating four distinct resistance states with a large on/off ratio (∼102) and significant variation in operation voltage (∼0.5 V). This rapid, reversible, and low-energy multi-level storage was achieved using an electrical pulse as short as 20 ns at low voltages of 1.0, 2.1, 3.0, and 3.6 V for the first, second, and third SET operation, and RESET operation, respectively. The multi-level storage capability, enabled by segregation-free Sb with enhanced thermal stability through nano-confinement effects, offers a promising pathway toward high-density PCRAM suitable for large-scale neuromorphic computing.
We have deposited In-doped $\mathrm{S}{\mathrm{b}}_{x}\mathrm{T}{\mathrm{e}}_{y}$ ($x:y=2:3$, 1:1, 3:1, 4:1) phase-change films, and studied their physics properties like crystallization temperature, activation energy, and optical band gap. On the basis of these parameters, a balance between thermal stability and crystallization speed can be found when In content is 20 at. %. We thus further studied their crystallization kinetics using the flash differential scanning calorimetry and the generalized Mauro-Yue-Ellison-Gupta-Allan viscosity model to investigate the potential fragile-to-strong crossover (FSC) in $\mathrm{I}{\mathrm{n}}_{20}{(\mathrm{S}{\mathrm{b}}_{2}\mathrm{T}{\mathrm{e}}_{3})}_{80}, \mathrm{I}{\mathrm{n}}_{20}{(\mathrm{SbTe})}_{80}, \mathrm{I}{\mathrm{n}}_{20}{(\mathrm{S}{\mathrm{b}}_{3}\mathrm{Te})}_{80}$, and $\mathrm{I}{\mathrm{n}}_{20}{(\mathrm{S}{\mathrm{b}}_{4}\mathrm{Te})}_{80}$ supercooled liquids. It was found that, $\mathrm{I}{\mathrm{n}}_{20}{(\mathrm{S}{\mathrm{b}}_{3}\mathrm{Te})}_{80}$ has a large crossover magnitude ($f$) of 2.4 with a distinct FSC behavior, but its maximum crystal growth rate (${U}_{\mathrm{max}}$) of $0.047\phantom{\rule{0.16em}{0ex}}\mathrm{m}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ is too low to satisfy the high-speed phase-change application. The crystal growth rate of $\mathrm{I}{\mathrm{n}}_{3}\mathrm{SbT}{\mathrm{e}}_{2}$ ($\mathrm{I}{\mathrm{n}}_{51}\mathrm{S}{\mathrm{b}}_{17}\mathrm{T}{\mathrm{e}}_{32}$) was found to be $0.08\phantom{\rule{0.16em}{0ex}}\mathrm{m}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ without distinct FSC. In contrast, $\mathrm{I}{\mathrm{n}}_{20}{(\mathrm{S}{\mathrm{b}}_{4}\mathrm{Te})}_{80}$ was demonstrated to have a larger ${U}_{\mathrm{max}}$ of $0.425\phantom{\rule{0.16em}{0ex}}\mathrm{m}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ and a distinct FSC behavior with a $f$ value of 2.6, which is larger than that of typical phase-change supercooled liquid $\mathrm{A}{\mathrm{g}}_{5.5}\mathrm{I}{\mathrm{n}}_{6.5}\mathrm{S}{\mathrm{b}}_{59}\mathrm{T}{\mathrm{e}}_{29}$. The results strongly support that, obvious FSC is unique only in some phase-change supercooled liquids, but not a universal dynamic feature.
The refractive index of commercial chalcogenide glasses (ChGs) available in the market is generally 2.4 to 2.7, which is relatively low and has huge room for improvement. In this paper, different ratios of Ag/Pb were doped into commercial glasses by the melt-quenching method to substantially increase their refractive index. The refractive index of the commercial Ge28Sb12Se60 glass was increased from 2.6 to 3.05 by external doping with 20 atomic percentage (at%) of Ag. And the refractive index of commercially available Ge33As12Se55 glass was increased from 2.45 to 2.88 by external doping with 9 at% of Pb. These improvements effectively reduce the thickness of commercial lenses at the same radius of curvature and focal length. The physical and optical properties of commercial glasses doped with Ag/Pb in different proportions were systematically characterized.
Understanding crystallization kinetics is essential to select the high-performance materials for phase-change memory. By ultrafast differential scanning calorimetry, we found the distinct fragile-to-strong crossover crystallization kinetics in ZnSb and Zn28Sb54Te18 supercooled liquids. Zn28Sb54Te18 inherits the excellent thermal stability around glass transition from ZnSb and exhibits faster crystal growth rate close to melting temperature (Umax is 9.1 m s−1) and larger crossover magnitude f (2.3), compared to the typical fragile-to-strong crossover material Ag-In-Sb2Te. Such a material with a distinct fragile-to-strong crossover is helpful to improve their thermal stability nearby glass transition temperature and accelerate the phase transition speed close to melting temperature.
We performed mechanical milling and Spark Plasma Sintering technology to fabricate a high Ge content chalcogenide glass, the Ge40As40Se20 glass, which locates outside the Ge-As-Se glass-forming domain. By using the optimal ball milling time of 50 h and sintering stress of 37.5 MPa, the large size Ge40As40Se20 bulk glasses were obtained, which possesses both large Vickers hardness of 369 Hv and relative high optical transmission of 43% (@5 and 9 μm). Moreover, it was found there are pores in the sintered glasses more or less, and the pore size and number significantly affect transmission, i.e., the optimal Ge40As40Se20 bulk glasses were demonstrated has the smallest and least pores. The combination of mechanical milling and low-temperature sintering methods has been confirmed to improve the glass formability and then obtain the high Ge content component with a potential high hardness glass to break through the limited mechanical property of chalcogenides.
In order to overcome the narrow glass-forming compositional range with traditional melt-quenching method, we here performed the mechanical milling and Spark Plasma Sintering technology to fabricate a high Ge content chalcogenide glass, the Ge40As40Se20 glass, which locates outside the Ge-As-Se glass-forming domain. By using the optimal ball milling time of 50 h and sintering stress of 37.5 MPa, the large size Ge40As40Se20 bulk glasses were obtained, which possesses both a large Vickers hardness of 369 Hv and a relative high infrared optical transmission of 43% (@5 and 9 μm). Moreover, it was found there are pores in the sintered glasses more or less, and the pore size and number significantly affect the transmission, i.e., the optimal Ge40As40Se20 bulk glasses were demonstrated has the smallest and least pores via scanning electron microscope. The combination of mechanical milling and low-temperature sintering methods has been confirmed can be used to improve the glass formability and then obtain the high Ge content component with a potential high hardness glass to break through the limited mechanical property of chalcogenides.
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