npj Computational Materials

Theoretical potential for low energy consumption phase change memory utilizing electrostatically-induced structural phase transitions in 2D materials (利用静电诱导的2D材料结构相变构建低能耗相变存储器)
Daniel A. Rehn, Yao Li, Eric Pop & Evan J. Reed
npj Computational Materials 3:44 (2017)
doi:10.1038/s41524-017-0059-2
Published online:22 January 2018
Abstract| Full Text | PDF OPEN

摘要:结构相变材料在信息存储设备应用方面极为重要。采用热驱动结构相变的相变存储器，可比主流非易失性存储技术实现更低的编程电压和更低的能量消耗。然而，由这种热驱动机制产生的废热通常不是最优化的，并可能成为其广泛应用的限制因素。新近理论预测显示，静电驱动的结构相变具有应用潜力，随后有报道提出，一些二维材料中存在一种无热机制，以非易失性方式动态调控这些材料的性质，实现潜在的更低能耗。本研究采用DFT计算对静电驱动相变和热诱导驱动相变所需能量差异进行理论比较。通过确定MoTe2单层和Ge2Sb2Te5薄膜的理论极限，我们发现，室温下单位体积的单层MoTe2中静电驱动相变所导致的能耗，仅为Ge2Sb2Te5中热驱动相变时绝热下限值的9％。此外，由于这些材料放出废热，实验报道的Ge2Sb2Te5中相变能耗比绝热下限大100~10000倍，使单层MoTe2基器件的能耗比Ge2Sb2Te5基器件降低了几个数量级。　　

Abstract:Structural phase-change materials are of great importance for applications in information storage devices. Thermally driven structural phase transitions are employed in phase-change memory to achieve lower programming voltages and potentially lower energy consumption than mainstream nonvolatile memory technologies. However, the waste heat generated by such thermal mechanisms is often not optimized, and could present a limiting factor to widespread use. The potential for electrostatically driven structural phase transitions has recently been predicted and subsequently reported in some two-dimensional materials, providing an athermal mechanism to dynamically control properties of these materials in a nonvolatile fashion while achieving potentially lower energy consumption. In this work, we employ DFT-based calculations to make theoretical comparisons of the energy required to drive electrostatically-induced and thermally-induced phase transitions. Determining theoretical limits in monolayer MoTe2 and thin films of Ge2Sb2Te5, we find that the energy consumption per unit volume of the electrostatically driven phase transition in monolayer MoTe2 at room temperature is 9% of the adiabatic lower limit of the thermally driven phase transition in Ge2Sb2Te5. Furthermore, experimentally reported phase change energy consumption of Ge2Sb2Te5 is 100–10,000 times larger than the adiabatic lower limit due to waste heat flow out of the material, leaving the possibility for energy consumption in monolayer MoTe2-based devices to be orders of magnitude smaller than Ge2Sb2Te5-based devices.

Editorial Summary

Phase change materials: less is more (MoTe₂相变材料：能耗少、用处广)

理论计算表明，单层MoTe2的静电驱动相变几乎没有废热放出。相变材料在热和信息存储方面拥有巨大的应用潜力，因为它们可在外部刺激下于不同物相（和性质）之间相互切换。然而，在这些转换过程中所散发的热量将限制器件的工作效率和进一步的小型化。现在，斯坦福大学的一个研究小组模拟了静电驱动的MoTe2相变过程和热驱动的Ge2Sb2Te5相变过程，发现MoTe2 单位体积的热耗散，比Ge2Sb2Te5的少100-10000倍，这是因为在后一种情况下，大部分能量变成了废热。MoTe2材料只会在系统中产生少量的废热，这使得其在低能耗、小体积器件方面具有广阔的应用前景。

Theoretical calculations reveal that the electrostatically driven phase transition of monolayer MoTe2 is accompanied by little heat waste. Phase change materials have enormous potential for thermal and information storage applications, as they can switch between different phases (and properties) with external stimuli. The amount of heat dissipated during these transitions can however limit the operation and further miniaturization of devices. A team from Stanford University has now modeled heat dissipation during the phase transition in electrostatically driven MoTe2 and thermally driven Ge2Sb2Te5: MoTe2 could consume 100‐10,000 times less energy per unit volume than Ge2Sb2Te5, as in the latter case most of the energy becomes heat waste. The small amount of heat that enters and leaves the system in the case of MoTe2 makes it very promising for low‐energy and low‐dimension devices.