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来说都是至关重要的。在非易失性存储器技术中，基于金属氧化物薄膜作为阻性开关层的阻性随机存取存储器具有高速、低操作电压、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，金属氧化物阻性随机存储器也面临着一些关键的挑战，如不可预测的形成过程。另一个挑战是从一层膜到另一层膜以及从一个点到另一个点的不同电阻状态。美国团队(Univ.在布法罗和普渡)和英国队(大学将开发一种高度创新、可扩展和先进的材料技术，以克服目前新兴电阻存储器的技术限制。材料平台是半导体行业中广泛使用的材料HfO2。与以前有关这种材料的工作不同，目前的项目将以新的方式精确设计HfO2微结构，以创建高度受控的开关性能。更广泛的技术影响建立在既定的行业合作基础上。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训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记忆概念；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/金属结构用于电阻随机存取存储器的导电丝是随机成核的，但本项目的设计结合了垂直排列的纳米复合材料或细粒柱状结构中的工程垂直界面来引导传导通道。这些预定义的接口能够形成高密度的精确且非随机的垂直导电路径，用于高性能的阻性随机存取存储器，而不需要高电压形成工艺。该项目通过将合成、表征、设计和制造具有目标特性和性能的阻性随机存取存储器器件的良好集成能力结合在一起来促进知识的发展。具体地说，它将把这个团队已经在外延纳米复合材料中展示的理想的工程材料系统转化为简单的二元氧化物，如硅上的HfO2。这些薄膜最初将通过脉冲激光沉积来生长。从脉冲激光沉积薄膜中学到的知识将被应用到工业溅射和原子层沉积工具中，以获得纳米工程HfO2基薄膜，其柱状晶尺寸很少。最后，制作了单个忆阻器和纵横制阵列结构，并对器件的关键参数进行了表征。此外，还将使用一套独特的表征工具来揭示器件性能和材料性能之间的相互作用。该项目的最终目标是通过在阻性开关金属氧化物层中形成受控的氧空位浓度和完善的导电通道，开发一种无成型、高度均匀、高密度、低功率、高开关比、卓越耐久的阻性存储器。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.