Materials World Network-- Ultrafast Switching of Phase Change Materials: Combined Nanosecond and Nanometer Exploration

闪存是目前固态存储器的工业标准，它依赖于越来越难以扩展的电荷感应。非易失性相变存储器（PCM）是一种很有前途的替代方案，因为它基于更容易检测局部可切换晶体与非晶态的电阻变化。这种PCM电池通常被配置为夹在两个电极之间的硫化物膜或棒，其中非晶/晶体转变分别通过淬火或缓慢冷却来实现，在电流感应加热超过玻璃化转变温度之后。PCM目前面临着许多挑战，这些挑战阻碍了它们成为非易失性存储器的主流解决方案，其中的核心是开关工艺本身。纳米尺度上的成核和结晶动力学也是一个值得关注的问题，因为它们将决定最终的开关速度，并涉及比特保留、保真度和疲劳的挑战。因此，这种开关过程的材料科学具有巨大的学术和工业兴趣，包括分别定义最终电阻变化和热扩散长度的局部电子和热特性的表征。为了解决这些问题，美国康涅狄格大学和英国兰开斯特大学之间的合作提议带来了大量和共生的专业知识，特别是在必要的纳米和空间尺度上同时进行的新型定量测量，包括用于绘制电极下相变的地下和深度剖面测量，如在实际的记忆细胞中。这种对PCM材料开发领域至关重要的综合专业知识，目前在全球任何一个实验室都不存在。该项目涉及材料和器件开发的工业合作，以及纳米级器件中材料相变映射的仪器仪表。PCM的局部电子和动态特性的主要重点将集中在美国，局部热学和地下测量将扎根于英国，美国（材料和设备）和英国（表征）的工业合作者将共同努力。互动将通过年度教师访问、为期一个月的学生交流和循环实验来加强。项目涉及重要的培训和外联部分，包括项目学生在整个大学学期访问外国同行，利用当地的专业知识和能力进行联合测量和技术转让，同时也受益于接触不同的教育体系。该提案旨在开发一种非破坏性的原位方法，用于PCM材料的实时开关过程。它基于电开关过程的高速纳米级探测，材料敏感超声力显微镜和纳米级热表征，其中合作机构拥有世界领先的专业知识。这将允许将局部材料特性和热传输与PCM材料和器件中的机械和化学缺陷，材料转化和开关现象联系起来，以及研究改善开关疲劳的方法。本研究将导致新的PCM材料及其加工和器件工程关键参数的改进，具有优越的开关速度，数据保留和开关疲劳，以及抵御现代存储器件尺寸减小和比特密度增加趋势的方法。

Flash memory, the present industry standard for solid state memory, is dependent on charge-sensing that is becoming increasingly difficult to scale. The non-volatile Phase Change Memory (PCM) is a promising alternative, as it is based on easier to detect resistance changes for locally switchable crystalline vs. amorphous states. Such PCM cells are generally configured as a chalcogenide film or rod sandwiched between two electrodes, where the amorphous/crystalline transition is achieved by quenching or slow cooling, respectively, after current induced heating beyond the glass transition temperature.There are multiple challenges for PCM that currently preclude them from becoming a mainstream solution for non-volatile memory, in the core of these lying the switching process itself. The dynamics of nucleation and crystallization on nanoscale are also an outstanding concern, as they will define the ultimate switching speeds and are implicated in challenges with bit retention, fidelity, and fatigue. The material science of this switching process is therefore of tremendous academic and industrial interest, including characterization of local electronic and thermal properties which define the ultimate resistance change and thermal diffusion length, respectively.To address these problems, this collaborative proposal between University of Connecticut, USA and Lancaster University, UK brings substantial and symbiotic expertise, specifically in novel quantitative measurements at the necessary simultaneous nanometer and spatial scales, including sub-surface and depth profile measurements for mapping the phase transition beneath an electrode as in practical memory cells. Such combined expertise, in critical for PCM materials development fields, presently do not exist in any single lab worldwide. The project involves industrial collaboration for both material and device development as well as instrumentation for materials phase change mapping in nanoscale devices. Primary emphasis on the local electronic and dynamic properties of PCM will be centered in the US, the local thermal and subsurface measurements will be rooted in the UK, with industrial collaborators based both in US (materials and devices) and UK (characterization). Interaction will be enhanced by annual faculty visits, month-long student exchanges, and round robin experiments. Project involves significant training and outreach component including project students visiting the foreign counterpart for an entire university term, leveraging the local expertise and capabilities for joint measurements and technology transfer while also benefitting from exposure to a different educational system.The proposal aims to develop a non-destructive in-situ methodology of real-time switching process in PCM materials. It is based on high speed nanoscale probing of electrical switching process, material sensitive ultrasonic force microscopy and nanoscale thermal characterization, where collaborating institutions have world leading expertise. That will allow to relate local material properties and heat transport with mechanical and chemical defects in PCM materials and devices, material transformation and switching phenomena, as well as to investigate approaches for improving switching fatigue. This research will lead to new PCM materials and improvement of key parameters of their processing and device engineering, with superior switching speed, data retention and switching fatigue and approaches for withstanding trends of decreasing dimensions and increasing bit density of modern memory devices.