Understanding the Origin of Low-Energy Operation Characteristics for Cr₂Ge₂Te₆ Phase-Change Material: Enhancement of Thermal Efficiency in the High-Scaled Memory Device

Abstract

Data recording based on the phase transition between amorphous and crystalline phases in a phase-change material (PCM) generally consumes a large amount of operation energy. Heat confinement and scaling down of the contact area between the PCM and electrode are effective strategies for reducing the operation energy in the memory device. Contrary to conventional PCM, such as Ge–Sb–Te compounds (GST), Cr2Ge2Te6 (CrGT) exhibits low thermal conductivity and low-energy memory operation characteristics even in a relatively large contact area. Herein, we show that the operation energy of the CrGT-based memory device is greatly reduced by scaling down. Based on the present results, an operation energy at subpico J order, which was achieved using carbon nanotubes or graphene nanoribbon in the GST-based device, can be realized in the contact area comparable to the product level in the CrGT-based device. The numerical simulation suggests that small thermal and electrical conductivities enhance the thermal efficiency, resulting in a small operation energy for amorphization. It was also found that the residual metastable phase after the amorphization process increased the operation energy for crystallization by the simulation. In other words, these results indicate that further small operation energy can be realized in the CrGT-based device by reducing the metastable phase volume.

Spin Glass Behavior in Amorphous Cr2Ge2Te6 Phase‐Change Alloy

“…[24] These features make CrGT a promising candidate for future spintronic and nanoelectronic applications in low dimensions. [25] However, CrGT can readily lose its long-range structural order in nanoscale electronic devices: a moderate voltage pulse of 3 V over 100 ns is already sufficient to trigger amorphization of CrGT, [26] which would significantly alter its magnetic properties. By applying a weaker pulse of 1.6 V over 30 ns, amorphous CrGT can be crystallized again.…”

Nonvolatile Isomorphic Valence Transition in SmTe Films

“…This causes compressive stress due to the difference in thermal expansion coefficients between SmTe and the surrounding material, followed by rapid cooling, or quenching, to restore the non-equilibrium mixed valence state. In the present device structure, the material placed on the heater electrode can be heated to temperatures ranging from 1400–1600 K, as predicted by numerical calculations . The introduced compressive stress, σ c , can be roughly estimated to be around 1.6 GPa using the formula σ c = Eα Δ T , where E represents the Young’s modulus (89.09 GPa for SmTe bulk material), α denotes the thermal expansion coefficient (16 ppm°C –1 for SmTe bulk material), and Δ T is the temperature difference from room temperature (1100 K). , The computed value of σ c is slightly smaller than the value required to achieve the mixed valence states with ρ of the as-deposited film, but it is comparable with σ for the as-deposited film.…”

Tailoring the oxygen concentration in Ge-Sb-O alloys to enable femtojoule-level phase-change memory operations

“…The melting of only the Sb 2 Te 3 nanolayers and the high thermal barrier brought by the TiTe 2 walls also result in about one order of magnitude reduction in RESET energy [66]. Sub-picojoule amorphization energy was also reported by using a Cr 2 Ge 2 Te 6 layered material [72].…”