Migration Barrier Layers for Epitaxial Topological SOT Materials
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Solution Overview
Problem
BiSb and YPtBi materials face challenges such as low melting points, large grain sizes, significant Sb migration issues, difficulty maintaining desired crystal orientations, and softness, which hinder their use in spin-orbit torque (SOT) devices.
Innovation Solution
A spin-orbit torque (SOT) device comprising a buffer layer, first and second migration barrier layers, a topological insulator (TI) or topological semi-metal (TSM) layer, an interlayer, a ferromagnetic layer, and a capping layer, with specific materials and orientations to enhance crystal orientation and prevent elemental migration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BiSb or YPtBi materials are used in SOT devices, then giant spin Hall effect and high electrical conductivity are achieved, but significant Sb migration and difficulty maintaining desired crystal orientation occur upon thermal annealing
Solution Approach 1:
A migration barrier layer is introduced as an intermediary between the BiSb/YPtBi topological insulator layer and the buffer layer. This barrier layer prevents Sb migration from the TI/TSM layer to the buffer layer during thermal annealing, while still allowing the TI/TSM layer to maintain its giant spin Hall effect and high electrical conductivity properties.
Solution Approach 2:
The migration barrier layer is deposited on the buffer layer before depositing the BiSb/YPtBi topological insulator layer. This preliminary action ensures that the barrier layer is already in place to prevent Sb migration during subsequent thermal annealing processes, addressing the migration issue before it occurs.
2Reliability
If BiSb materials are used, then high electrical conductivity is achieved, but low melting point and softness cause damage during ion milling
Solution Approach 1:
The migration barrier layer serves as a protective cushion deposited beforehand on the buffer layer. This layer protects the soft BiSb topological insulator layer from damage during ion milling by absorbing or distributing the mechanical stress, while still allowing the BiSb layer to maintain its high electrical conductivity for SOT device operation.
3Manufacturing precision
If thermal annealing is performed to improve crystal orientation, then desired (012) or (001) orientation is achieved, but Sb migration increases due to film roughness
Solution Approach 1:
The migration barrier layer acts as an intermediary that allows thermal annealing to be performed for improving crystal orientation to the desired (012) or (001) orientation while simultaneously preventing Sb migration. The barrier layer blocks the diffusion path of Sb atoms during the thermal annealing process, decoupling the benefits of thermal treatment from the harmful migration effects.
Data Source
AI summary
The present disclosure generally relates to topological insulator (TI) based or topological semi-metal (TSM) based spin-orbit torque (SOT) devices. The SOT device comprises a buffer layer, a first migration barrier layer, a TI or TSM layer, a second migration barrier layer, an interlayer, a ferromagnetic layer, and a capping layer. The TI or TSM layer is disposed in contact with the first and second migration barrier layers. The SOT device can also comprise a buffer layer, a ferromagnetic layer, an interlayer, a first migration barrier layer, a TI or TSM layer, a second migration barrier layer, and a capping layer. The TI or TSM layer is disposed in contact with the first and second migration barrier layers.