Collaborative Research: ECCS-EPSRC: Development of uniform, low power, high density resistive memory by vertical interface and defect design

非易失性存储器对于现代计算的各个方面以及物联网和神经形态计算等下一代数字技术都至关重要。在非易失性存储器技术中，基于金属氧化物膜作为阻变层的阻变存储器具有高速、低工作电压、低功耗和良好的耐久性的潜力，从而能够以最低的成本实现最高的性能。然而，金属氧化物电阻式随机存取存储器也面临着一些关键的挑战，如不可预测的形成过程。另一个挑战是从一个膜到另一个膜以及跨每个膜从一个点到另一个点的可变电阻状态。美国团队（布法罗大学和普渡大学）和英国团队（剑桥大学）之间的合作项目将开发一种高度创新、可扩展和先进的材料技术，以克服新兴电阻存储器目前的技术限制。材料平台是HfO 2，这是半导体行业中广泛使用的材料。与以前对这种材料的研究不同，目前的项目将以新的方式精确设计HfO 2微结构，以创造高度可控的开关特性。更广泛的技术影响建立在已建立的行业合作基础上。该研究计划与所有三个校区的教育和推广计划很好地结合在一起，包括：1）在国际研究环境中培养具有多学科研究技能的年轻研究人员; 2）通过教学在材料科学和工程课程中实施电阻存储概念; 3）通过推广计划向更广泛的受众传播研究成果。虽然常用的金属/金属氧化物/电阻式随机存取存储器的金属结构具有随机成核的导电丝，该项目的设计在垂直排列的纳米复合材料或细颗粒柱状结构中纳入了工程垂直界面，以引导导电通道。这些预定义的界面使得能够形成用于高性能电阻式随机存取存储器的具有高密度的精确且非随机的垂直导电路径，而不需要高电压形成工艺。该项目通过结合良好的集成能力来合成，表征，设计和制造具有目标属性和性能的电阻式随机存取存储器器件来提高知识。具体来说，它将把该团队已经在外延纳米复合材料中证明的理想工程材料系统转化为简单的二元氧化物，如Si上的HfO 2。这些薄膜最初将通过脉冲激光沉积生长。从脉冲激光沉积生长的薄膜中学到的知识将被应用到溅射和原子层沉积的工业工具中，以实现具有约几个nm尺寸的柱状晶粒的纳米工程HfO 2基薄膜。最后，个别忆阻器和交叉阵列结构将被制造，和设备的特征的关键参数。此外，将使用一组独特的表征工具来揭示器件性能和材料特性之间的相互作用。该项目的最终目标是开发一种无成型、高度均匀、高密度、低功耗、高开/关比、通过在电阻开关金属氧化物层中形成受控的氧空位浓度和完美的导电通道，实现上级耐久电阻存储器。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的评估，被认为值得支持影响审查标准。

Non-volatile memory is critical for all aspects of modern computing, as well as for next generation of digital technologies like the Internet of Things and neuromorphic computing. Among non-volatile memory technologies, resistive random access memory based on metal oxide films as resistive switching layers has the potential for high-speed, low operation voltage, low power consumption, and good endurance properties that enable the highest performance at the lowest cost. However, metal oxide resistive random access memory also faces some critical challenges such as the unpredictable forming process. Another challenge is the variable resistive states from one film to another and from one point to another across each film. The collaborative project between the US team (Univ. at Buffalo and Purdue) and the UK team (Univ. of Cambridge) will develop a highly innovative, scalable, and advanced materials technology to overcome the current technical limitations of emerging resistive memory. The materials platform is HfO2, a widely used material in the semiconductor industry. Unlike previous work on this material, the current project will precisely engineer HfO2 microstructures in new ways to create highly controlled switching properties. The broader technological impacts are built on established industry collaborations. The research program is well integrated with education and outreach programs at all three campuses, including: 1) training young researchers with multidisciplinary research skills in an international research environment; 2) implementing resistive memory concepts in materials science and engineering curricula through teaching; 3) disseminating research findings to broader audiences through outreach programs.While commonly-used metal/metal oxide/metal structures for resistive random access memory have conduction filaments that are nucleated randomly, the design in this project incorporates engineered vertical interfaces in either vertically aligned nanocomposite or fine-grained columnar structures to guide the conduction channels. These pre-defined interfaces enable the formation of precise and non-random vertical conducting paths with high densities for high performance resistive random access memory, without the need for a high voltage forming process. This project advances knowledge by combining well-integrated capabilities to synthesize, characterize, design, and fabricate resistive random access memory devices with targeted properties and performance. Specifically, it will translate the ideal engineered materials systems which has been already demonstrated by this team in epitaxial nanocomposites to simple binary oxides such as HfO2 on Si. These films will be initially grown by pulsed laser deposition. The knowledge learned from the films grown by pulsed laser deposition will be then implemented to industrial tools of sputtering and atomic layer deposition to achieve nanoengineered HfO2-based films with ~few nm sized columnar-grains. Finally, individual memristors and crossbar array structures will be fabricated, and the key parameters of the devices characterized. Furthermore, a set of unique characterization tools will be used to reveal the interplay between the device performance and the materials properties. The ultimate goal of the project is to develop a forming-free, highly uniform, high density, low power, high on/off ratio, superior endurance resistive memory through the formation of controlled oxygen vacancy concentration and perfect conducting channels in resistive switching metal oxide layers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.