Computer simulation study of rare events in magnetic nanosystems: error rates and energy barriers in STT-MRAM cells

该项目的主要目标是利用计算机模拟(在实验支持下)对具有许多亚稳态的物理系统中的罕见事件进行理论研究，并以新兴的一代新型计算机存储器为例：自旋-转移-扭矩磁随机存取存储器(STT-MRAM)。根据这个总任务，这项建议的部分目标是：(1)彻底了解STT-MRAM单元中的开关过程(使用数值研究和支持实验测量)，目的是识别典型的开关场景，并预测开关电流与MRAM单元参数和环境条件的依赖关系。(2)使用有限温度下MRAM单元的全尺寸大规模并行微磁模拟来计算STT-MRAM单元的读写错误率(并通过对MRAM单元阵列的大规模实验来验证这些计算)。(3)预测在广泛的温度和时间范围内STT-MRAM单元的读写错误率。STT-MRAM单元中的信息寿命使用可靠的数值方法(将在本项目的框架中开发)来评估能量势垒。为了实现这些部分目标，通用数值研究实验室的理论小组打算开发：(I)基于GPU的新的数值方法来大规模并行地模拟多层纳米元件中的开关过程，以及(Ii)直接确定具有多个亚稳态的系统中的能垒的先进方法，这也将解释通过几个中间局部能量最小值在给定的两个状态之间转变的可能性。预期的项目结果将极大地提高我们对具有许多亚稳态的磁系统中的长时间磁化动力学的理解，特别是对新一代磁存储器(STT-MRAM)中的开关过程有深刻的物理见解。

The main goal of the project is the theoretical study using computer simulations (with experimental support) of rare events in physical systems with many metastable states, taking as an example an emerging generation of novel computer memory: spin-transfer-torque magnetic random access memory (STT-MRAM). According to this general task, partial goals of this proposal are: (1) To achieve thorough physical understanding of switching processes in STT-MRAM cells (using numerical studies and supporting experimental measurements) with the purpose to identify typical switching scenarios and to predict the dependence of the switching current on the MRAM cell parameters and on the environmental conditions.(2) To calculate Write and Read Error Rates of STT-MRAM cells using full-scale massively parallel micromagnetic simulations of MRAM cells at finite temperatures (and to verify these calculations by large-scale experiments on MRAM cell arrays) in a broad range of temperatures and times.(3) To predict the information life time in STT-MRAM cells using reliable numerical methods (to be developed in frames of this project) for the evaluation of energy barriers.In order to achieve these partial goals, the theory group of General Numerics Research Lab intends to develop:(i) new GPU-based numerical methods for massively parallel Langevin-dynamics modeling of switching processes in multilayer nanoelements, and (ii) advanced methods for the direct determination of energy barriers in systems with multiply metastable states, which would also account for the possibility of a transition between two given states via several intermediate local energy minimaExpected project results should greatly improve our understanding of the long-time magnetization dynamics in magnetic systems with many metastable states in general, and obtain deep physical insights into the switching processes in the new generation of magnetic memory (STT-MRAM) in particular.