我们已经测量了临界相变条件的电脉冲在Ge 2Sb 2 Te 5纳米柱相变存储器件通过构建一个全面的电阻图作为脉冲参数（宽度，幅度和后沿）的函数。我们的测量结果表明，加热方案和接触几何形状的细节在确定器件的最终相组成中起着主导作用，使得非均匀加热方案促进部分非晶化/结晶化，用于宽范围的脉冲参数，从而实现数据存储应用的多个电阻水平。此外，我们发现，在重复的开关实验中的骤回电压和设置/复位电阻的波动有关的电流分布的细节，使一个均匀的电流注入几何形状（即圆形接触）有利于更可再现的开关参数。这表明，纳米级相变存储器器件中可能的几何缺陷可以通过修改有源硫属化物层中的精确电流分布而在最小可能器件的性能中发挥重要作用。我们提出了一个三维有限元模型的电热物理提供深入了解的基本物理机制的开关动力学，以及定量占的缩放行为的开关电流在圆形和矩形接触几何形状。在脉冲持续时间内的热分布的计算的时间演变示出了在矩形接触的不同功能，提供证据的局部热点在电流注入部位的尖角处，由于电流拥挤效应导致所观察到的行为。
英文摘要：
We have measured the critical phase change conditions induced by electrical pulses in Ge2Sb2Te5 nanopillar phase change memory devices by constructing a comprehensive resistance map as a function of pulse parameters (width, amplitude and trailing edge). Our measurements reveal that the heating scheme and the details of the contact geometry play the dominant role in determining the final phase composition of the device such that a non-uniform heating scheme promotes partial amorphization/crystallization for a wide range of pulse parameters enabling multiple resistance levels for data storage applications. Furthermore we find that fluctuations in the snap-back voltage and set/reset resistances in repeated switching experiments are related to the details of the current distribution such that a uniform current injection geometry (i.e. circular contact) favors more reproducible switching parameters. This shows that possible geometrical defects in nanoscale phase change memory devices may play an essential role in the performance of the smallest possible devices through modification of the exact current distribution in the active chalcogenide layer. We present a three-dimensional finite element model of the electro-thermal physics to provide insights into the underlying physical mechanisms of the switching dynamics as well as to quantitatively account for the scaling behaviour of the switching currents in both circular and rectangular contact geometries. The calculated temporal evolution of the heat distribution within the pulse duration shows distinct features in rectangular contacts providing evidence for locally hot spots at the sharp corners of the current injection site due to current crowding effects leading to the observed behaviour.
The Effect of Twisting Angle on the Electronic Properties and Electron Transport and Hall Effect in the Twisted Circular and Rectangular Graphene and Graphene/Boron-Nitride Channels
