SHF: Small: Collaborative Research: Energy Efficient Strain Assisted Spin Transfer Torque Memory

非易失性随机存取存储器（NV-RAM）通常使用称为自旋转移矩随机存取存储器（STT-RAM）的设备构建，其主要成分是圆形纳米磁体。通过传递自旋极化电流将位“写入”到纳米磁体中，所述自旋极化电流的极性确定位“1”还是位“0”被写入。这些状态之间的能量势垒防止磁化由于热噪声而自发地切换，使器件非易失性。不幸的是，写入电流中消耗的能量是当今CMOS器件中消耗的能量的100-1000倍，这是为非易失性付出的巨大代价。该项目旨在证明，用表面声波（SAW）暂时降低“向上”和“向下”磁化状态之间的能量势垒可以显著降低写入位所需的电流，并将能量耗散降低几个数量级。这将使SAW辅助STT-RAM成为嵌入式处理器、物联网、大型数据中心和需要低能耗存储器的网络物理系统的理想选择。至少3名博士生将接受互补纳米制造、纳米表征和计算机建模技术的培训。研究人员将为高中生举办一个纳米磁性研讨会，并将在他们的实验室里接待代表性不足的K-12学生一个夏季，以及利用“纳米日”计划接触高中生。本研究项目的关键技术方法将涉及以下互补的实验和建模研究方向：（i）模拟在存在热噪声的情况下应变和自旋转移力矩（STT）对磁化切换的组合效应（iii）声波引起的STT写入电流减小的概念验证演示。通过这项研究所产生的知识将导致更好地理解应变和自旋扭矩对开关纳米磁存储器元件的综合影响，以及在存在热噪声的情况下的开关概率。如果成功，它将展示一个低能量的范例写入信息的非易失性纳米磁性存储设备。这一奖项反映了NSF的法定使命，并已被认为是值得支持的评估使用基金会的智力价值和更广泛的影响审查标准。

Non-volatile random access memory (NV-RAM) is often built with a device called spin transfer torque random access memory (STT-RAM), the main constituent of which is a circular nano-magnet. A bit is "written" into the nano-magnet by passing a spin-polarized current whose polarity determines whether bit "1" or bit "0" is written. The energy barrier between these states prevents the magnetization from switching spontaneously due to thermal noise, making the device non-volatile. Unfortunately, the energy dissipated in the writing current is 100-1000 times more than the energy dissipated in today's CMOS devices, which is a large cost to pay for non-volatility. This project seeks to demonstrate that temporarily reducing the energy barrier between the "up" and "down" magnetization states with surface acoustic waves (SAW) can significantly lower the current needed to write a bit and reduce the energy dissipation by orders of magnitude. This would make the SAW-assisted STT-RAM ideal for embedded processors, internet of things, large data centers and cyber-physical systems requiring low energy memory. At least 3 PhD students would be trained on the techniques of complementary nano-fabrication, nano-characterization and computer modeling. The investigators will hold a nano-magnetism workshop for high school students and will host under-represented K-12 students in their labs for a summer month, as well as leverage the "Nano-Days" program to reach out to high school students. The key technical approach in this research project will involve the following complementary experimental and modeling research directions: (i) Modeling the combined effect of strain and spin transfer torque (STT) on the magnetization switching in the presence of thermal noise (ii) Experimental demonstration of strain induced reduction in STT write current in optimized devices (guided by the modeling effort) (iii) Proof-of-concept demonstration of acoustic wave induced reduction in STT write current. The knowledge generated by this research would lead to better understanding of the combined effect of strain and spin torque on switching nano-magnetic memory elements and the switching probability in the presence of thermal noise. If successful, it would demonstrate a low energy paradigm for writing information in non-volatile nano-magnetic memory devices.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.