Abstract
Phase-change memory utilizing amorphous-to-crystalline phase-change processes for reset-to-set operation as a nonvolatile memory has been recently commercialized as a storage class memory. Unfortunately, designing new phase-change materials (PCMs) with low phase-change energy and sufficient thermal stability is difficult because phase-change energy and thermal stability decrease simultaneously as the amorphous phase destabilizes. This issue arising from the trade-off relationship between stability and energy consumption can be solved by reducing the entropic loss of phase-change energy as apparent in crystalline-to-crystalline phase-change process of a GeTe/Sb2Te3 superlattice structure. A paradigm shift in atomic crystallography has been recently produced using a quasi-crystal, which is a new type of atomic ordering symmetry without any linear translational symmetry. This paper introduces a novel class of PCMs based on a quasicrystalline-to-approximant crystalline phase-change process, whose phase-change energy and thermal stability are simultaneously enhanced compared to those of the GeTe/Sb2Te3 superlattice structure. This report includes a new concept that reduces entropic loss using a quasicrystalline state and takes the first step in the development of new PCMs with significantly low phase-change energy and considerably high thermal stability.
Highlights
Phase-change memory utilizing amorphous-to-crystalline phase-change processes for reset-to-set operation as a nonvolatile memory has been recently commercialized as a storage class memory
It should be noted that activation energies which correspond to the phase-changes from amorphous to QC and from QC to approximant crystal (AC) state of Al–Mn–Si alloys such as Al55Mn20Si25, Al60Mn15Si25, Al65Mn15Si20 are comparable with that from amorphous to crystalline state of Ge–Sb–Te (2.34 eV) which supports that amorphous and QC phase is stable enough to sustain each phase at room temperature even though they are not the most stable state[26]
The phase change characteristics of Al–Mn–Si alloys were investigated using electrical cells of phase-change materials (PCMs) based on phase-change temperature and energy of melt-quenched ribbons at speeds of 106 K/s
Summary
Phase-change memory utilizing amorphous-to-crystalline phase-change processes for reset-to-set operation as a nonvolatile memory has been recently commercialized as a storage class memory. These structures have discrete point-group symmetry that is not allowed for periodic systems of conventional crystals[16,17,18]. We introduce a novel class of PCMs based on a quasicrystalline-to-approximant crystalline phase-change process, whose phase-change energy and thermal stability are enhanced to a higher extent than those of the GeTe/Sb2Te3 superlattice structure This is accomplished by suppressing entropic loss, where fast phase-change speed (< 10 ns) and symmetricity and linearity for neuromorphic computing are secured, simultaneously. Our report reduces entropic loss by utilizing QCs and opens a door to the development of new PCMs with super-low phase-change energy and super-high thermal stability
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