NSF-BSF: CNS Core: Small: Reliable and Zero-Power Timekeepers for Intermittently Powered Computing Devices via Stochastic Magnetic Tunnel Junctions

该项目旨在推进低功耗、无电池、能量收集嵌入式系统的最先进的计时技术。这些系统必须在多个频繁的电源故障中执行计算和传感任务。这种间歇操作需要强烈的时间意识，以确保不浪费能量和计算结果不陈旧。现有的计时器（即实时时钟）需要大量的能量来打开和操作，相对较大（毫米级），重新启动缓慢，并且使用的能量与电源故障的长度成正比（可能很长）。该项目利用新兴的纳米级非易失性磁随机存取存储器（MRAM）器件的独特特性，特别是可调节的数据保留长度，来创建低功耗、可调节的超小型计时设备。系统可以设置计时器的几个位，稍后检查它们，看看哪些丢失了信息。通过将每个比特或比特数组调整到特定的时间长度，系统可以测量时间，而不管是否发生电源故障。这样的计时器需要同样的能量，如果它的时间中断一秒钟，一天，或一年，任意精度取决于所使用的磁性元件的数量和特性。该项目跨越系统堆栈来实现这个计时器的好处；探索电路设计、架构和系统范例，将这种新的计时设备嵌入间歇性计算的环境中：作为运行时时钟、中断源、数据和输入/输出（I/O）控制器的替代方案，以及作为过期内存分配器。这些模块可供应用程序开发人员使用，以提高其程序的及时性。在这个项目中开发的技术将使一种重要的新兴计算机系统能够更有效和准确地计时。无电池和能量收集计算设备为物联网提供了一个更可持续的未来，并使许多健康、农业和智能基础设施应用成为可能。在远程供电传感器中消除电池将减轻由于电池磨损和更换而导致的日益增长的废物流。该项目设备和系统的制造和最终分销将为未来的无电池系统提供更精确的计时模块，增强无电池系统的可靠性、安全性和及时性。由此产生的工具和实验结果将实现无电池器件的鲁棒交叉堆栈模拟和磁存储器件的制造方法。该项目的成果将整合到几个正在进行的外展活动中，让K-12和本科生了解嵌入式计算的使用和应用。这项工作将培养研究生在计算、材料和物理方面的基本技能，并通过GoBabyGo！学生们用玩具车为行动不便的孩子们制作电动轮椅。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This project seeks to advance the state-of-the-art in timekeeping for low-power, battery-free, energy harvesting embedded systems. These systems must perform computation and sensing tasks across multiple, frequent power failures. This intermittent operation requires a strong sense of time to ensure no energy is wasted and computed results are not stale. Existing timekeepers (i.e. real-time clocks) require significant amounts of energy to turn on and operate, are relatively large (millimeter scale), are slow to restart, and use energy proportional to the length of a power failure (which can be impractically long). This project takes advantage of the unique properties of emerging nano-scale non-volatile magnetic random-access memory (MRAM) devices, particularly adjustable data retention length, to create orders of magnitude lower power, adjustable, ultra-small timekeeping devices. A system can set a few bits of the timekeeper and check them later to see which ones have lost information. By tailoring each bit, or array of bits, to particular lengths of time, the system can measure time regardless of whether a power failure occurred. Such a timekeeper requires the same amount of energy if it times an outage of one second, one day, or one year, with arbitrary accuracy depending on the number and characteristics of the magnetic elements used. The project cuts across the system stack to realize the benefits of this timekeeper; exploring circuit designs, architectural, and system paradigms to embed this new timekeeping device in the context of intermittent computing: as an alternative to a runtime clock, an interrupt source, a data and input/output (I/O) controller, and as an expiring memory allocator. These modules are made available to application developers to enhance the timeliness of their programs.The technologies developed in this project will enable more efficient and accurate timekeeping for an important emerging class of computer systems. Batteryless and energy harvesting computing devices offer a more sustainable future for the Internet of Things and enable numerous health, agriculture, and intelligent infrastructure applications. The elimination of batteries in remotely powered sensors will mitigate the growing waste stream resulting from battery wear out and replacement. The fabrication and eventual distribution of the devices and systems from this project will provide a more accurate timekeeping module for future batteryless systems, enhancing the reliability, security, and timeliness of batteryless systems. The resulting tools and experimental results will enable robust cross-stack simulation for battery-free devices and fabrication methods for magnetic memory devices. Outcomes of this project will be integrated into several ongoing outreach activities that expose K-12 and undergraduate students to the usage and application of embedded computing. This effort will train graduate students in essential skills across computing, materials, and physics and engage them in mentoring, teaching, and outreach activities via GoBabyGo!– where students help build power wheelchairs from ride-on toy cars for children with mobility issues.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.