Development of Tera-bit class high speed nonvolatile magentic memories

为了实现太比特密度和高存取速度的磁性非易失性存储器，对一种新的共享功能器件概念进行了实验和数值研究。在该单元结构中，用于位信息载体的数据存储层和用于数据写入的交换层通过磁耦合垂直集成。1)通过数值模拟比较了偶极耦合和层间交换耦合两种不同的功能积分机制，发现交换耦合在细槽内从开关层到存储层的转矩传递更优。2)采用自对准工艺制备了最小图案尺寸为200 nm的交叉点（CP）存储电池，其中磁性多层条带结构具有覆盖的导体图案，用作干蚀刻的掩膜。通过对所制备的CP电池的磁阻测量，证实了偶极子耦合的良好定义，这导致了磁化反转场的急剧减小。3)对由软磁CoFe层和硬磁TbFe层组成的交换耦合双层电池进行了热辅助磁化反转。电流诱导的局部焦耳加热降低了tfe层的磁各向异性，导致双层的磁化反转场明显减小。脉冲激光加热也证实了高速运行。4)利用新开发的程序引入宏观尺度模型，对高温磁化过程进行了数值分析。详细阐明了交换耦合双层中热辅助磁化反转的机理。对磁性能、层间结构和层间交换耦合刚度进行了优化，实现了优异的功能共享性能。优化后的垂直磁化电池的横向尺寸为10 nm，具有实际的数据稳定性和低功耗的存储操作。少

Experimental and numerical studies on a novel device concept of sharing function have been performed to realize a magnetic nonvolatile memory with terabit density and high access speed. In the proposed cell structure, data storage layer for bit information carrier and switching layer for data writing are vertically integrated through magnetic coupling.1)Two different functional integrating mechanism of dipole coupling and inter-layer exchange coupling have been compared by numerical simulation, and it was found that the exchange coupling exhibits superior torque transmitting from switching to storage layer in the fine cell.2)A cross-point (CP) memory cell with the minimum pattern size of 200 nm was fabricated by a self-aligned process, where a magnetic mulilayer strip was structured with an over-laid conductor pattern used as a mask for dry-etching. Well defined dipole coupling was confirmed from magnetoresistive measurements for the fabricated CP cell, which leads to the drastic reduc … More tion of the magnetization reversal field.3)Thermally assisted magnetization reversal was performed for an exchange coupled bi-layer cell, consisted of soft magnetic CoFe and hard magnetic TbFe layer. The current induced local Joule heating decreases the magnetic anisotropy in the TbFe layer, which results in the marked decrease of the magnetization reversal field of the bi-layer. A high speed operation was also confirmed with the pulsed laser heating.4)Numerical analysis for the magnetization process at high temperature was carried out with the newly developed program introducing a macro scale model. Detailed mechanism of thermally assisted magnetization reversal in the exchange coupled bi-layer has been clarified. Magnetic properties, the layer structure and the inter-layer exchange coupling stiffness have been optimized to realize the superior functional sharing performance. Practical data stability and low power memory operation have been confirmed for the optimized perpendicularly magnetized cell with an order of 10 nm lateral dimension. Less