Fundamental Investigation of Charge Transport and Memory Switching in Amorphized Phase-Change Nanowires

摘要：技术：PI将研究从Ge-Sb-Te合金自组装的相变纳米线（NW）的电学特性，Ge-Sb-Te合金是用于非易失性随机存取存储器器件的重要材料。硫属化物材料（例如，Ge-Sb-Te合金）在非易失性光学和电存储应用领域中占主导地位，因为它们的可逆的结晶-非晶相变，其由光学反射率和电阻率的大的变化表示。然而，在存储器装置应用中实现这些优点仍然受限于对高可扩展性、低功率消耗以及对电输运、阈值切换和来自非晶相的再结晶机制的基本理解的要求。这些挑战激发了基于自下而上方法的具有亚光刻特征的纳米结构材料的设计和理解。在该项目期间，他们将开发基于NW的实验，以系统地了解尺寸相关的纳米级电气开关和相变的基本特性，这些特性对于指导未来存储器件的设计至关重要。相变性质的演变，特别是对于非晶相纳米结构玻璃，作为尺寸的函数，还没有得到充分的探索，主要是由于缺乏材料系统，可以以可控的方式制备，具有足够的尺寸控制，而不会损坏表面，发生在自上而下的光刻技术。NW相变材料的研究将提供有价值的信息的尺寸缩放的相变机制下到子20纳米的长度尺度，不能很容易地从自上而下的图案化系统。拟议的研究将建立在PI实验室最近在相变纳米线领域取得的突破基础上，展示了记忆切换和显着的尺寸依赖特性。他们将寻求获得答案的重要问题是：什么是在非晶相的导电机制及其尺寸和成分的依赖性;阈值切换和成核从非晶到结晶状态的机制是什么;应力或电子弛豫在非晶相的时间漂移行为中起什么作用。PI将结合联合收割机新颖的合成，结构表征和详细的电学测量来回答这些有趣的问题。为了实现这些目标，将采取以下方法：1）合成复杂的硫族化物纳米线，精确控制其化学组成和尺寸。用介电材料覆盖纳米线以防止表面氧化。2）研究相变纳米线器件在非晶状态下的导电机制。3）非晶状态下相变纳米线的时间漂移行为4）非晶相纳米线中的成核和阈值开关及其统计。非技术性：自下而上的自组装纳米结构方法提供了一种创建高效纳米系统的独特方式，该纳米系统将具有任何传统技术都不可能实现的功能。这种存储器系统的发展将对各种应用产生巨大的影响，例如更便宜和高效的计算机随机存取存储器系统，以及无处不在的便携式设备，例如ipod和数码相机。研究和教育活动将通过本科生参与研究计划来整合，将新的研究成果纳入教学模块，并培训来自费城地区的高中和大学教师，学生来自少数民族和代表性不足的部分。

Abstract:Technical: The PI will study the electrical properties of phase-change nanowires (NW) self-assembled from Ge-Sb-Te alloys, which are important materials for their use in non-volatile random access memory devices. Chalcogenide materials (e.g., Ge-Sb-Te alloys) have been dominant in the field of nonvolatile optical and electrical storage applications because of their reversible crystalline-amorphous phase transition that is signified by large changes in the optical reflectivity and electrical resistivity. The realization of these advantages in memory device applications is, however, still limited with requirements for high scalability, low-power consumption and fundamental understanding of electrical transport, threshold switching and recrystallization mechanism from the amorphous phase. These challenges motivate the design and understanding of nanostructured materials with sub-lithographic features based on bottom-up approach. During the project they will develop NW-based experiments to systematically understand fundamental properties of size-dependent nanoscale electrical switching and phase transitions that are important in order to instruct the design of future memory devices. The evolution of the phase-change properties especially for amorphous phase nanostructured glass as a function of size has not been fully explored, mostly due to the lack of material systems that can be prepared in a controllable fashion with sufficient size control and without damaging the surfaces that occurs in top-down lithographic techniques. The study of NW phase-change materials will provide valuable information on the size-scaling of the phase-change mechanism down to sub-20 nm lengthscales that cannot be easily obtained from top-down patterned systems. The proposed research will be built upon the recent breakthroughs in the PI's laboratory in the area of phase change NWs, with demonstration of memory switching and remarkable size-dependent properties. The important questions that they will seek to obtain answers are: what is the conduction mechanism in the amorphous phase and its size and composition dependence; what is the mechanism of threshold switching and nucleation from amorphous to crystalline state; what role does stress or electronic relaxations play in temporal drift behavior of the amorphous phase. The PI will combine novel synthesis, structural characterization with detailed electrical measurements to answer these intriguing questions.To accomplish the objectives, the following approach will be undertaken:1) Synthesis of complex chalcogenide nanowires with precise control over their chemical composition and size. Capping of NWs with dielectric materials to prevent surface oxidation.2) Study the conduction mechanisms in amorphous state of phase change nanowire devices.3) Temporal drift behavior of phase change nanowires in the amorphous state4) Nucleation and threshold switching and their statistics in amorphous phase nanowires.Non-technical: Bottom up approach to self assembled nanostructures presents a unique way of creating highly efficient nanosystems that will have functionalities that are not possible with any conventional technology. The development of such a memory system will have tremendous impact on a variety of applications such as cheaper and highly efficient computer random access memory systems, and ubiquitous portable devices such as ipods and digital cameras. Research and educational activities will be integrated by the involvement of undergraduates in the research program, incorporating new research results in the teaching module, and training high school and college teachers from the Philadelphia district with student population from minority and underrepresented sections.