Recessed BiSb SOT Reader for Sensing and Fabrication Protection
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Solution Overview
Problem
BiSb materials face challenges such as low melting points, large grain sizes, significant Sb migration issues, difficulty maintaining desired crystal orientation, and softness, which hinder their use in spin-orbit torque (SOT) devices.
Innovation Solution
A SOT device design featuring a BiSb layer recessed from the media facing surface (MFS) with a specific distance, combined with a free layer extending beyond the recessed BiSb layer, and optionally including notches and insulation layers to enhance current flow and orientation, thereby improving signal-to-noise ratio and down-track resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BiSb material is used as spin Hall layer, then giant spin Hall effect and high electrical conductivity are achieved, but low melting point and softness cause difficulty in fabrication and damage during ion milling
Solution Approach 1:
A buffer layer is introduced between the BiSb spin Hall layer and the underlying substrate/shield structure. This buffer layer serves as a protective intermediary that prevents direct damage to the soft BiSb material during ion milling and fabrication processes, while still allowing the BiSb layer to function effectively for generating spin Hall effect.
Solution Approach 2:
The buffer layer is deposited beforehand to provide mechanical protection and structural support to the BiSb layer before subsequent fabrication steps including ion milling. This pre-positioned protective layer cushions the BiSb material from harsh processing conditions that would otherwise damage or destroy it.
2Measurement precision
If BiSb layer is placed at media facing surface for optimal sensing, then field sensing capability is improved, but Sb migration and film roughness issues worsen upon thermal annealing
Solution Approach 1:
The buffer layer acts as a protective intermediary between the BiSb layer and the media facing surface environment. It prevents direct exposure of the BiSb layer to conditions that cause Sb migration during thermal annealing, while still allowing the BiSb layer to be positioned for optimal field sensing performance.
Solution Approach 2:
The buffer layer serves as a sacrificial or protective layer that can be optimized for thermal stability rather than spin Hall effect performance. It absorbs the thermal stress and prevents degradation of the BiSb layer during annealing processes, sacrificing its own structural integrity to protect the functional BiSb layer.
3Strength
If BiSb layer is recessed from media facing surface to protect from damage, then material protection is improved, but shield-to-shield spacing increases reducing field sensing
Solution Approach 1:
The buffer layer extends to the media facing surface to maintain optimal shield-to-shield spacing for field sensing, while the recessed BiSb layer is protected from direct exposure to harsh environments. The buffer layer mediates between the need for protection and the need for sensing performance.
Solution Approach 2:
The structure transitions from a planar configuration to a recessed configuration in the vertical dimension. The BiSb layer is recessed into the substrate while the buffer layer maintains the surface profile, creating a three-dimensional structure that simultaneously achieves protection and sensing performance.
4Manufacturing precision
If thermal annealing is applied to improve crystal orientation, then desired (012) or (001) orientation is achieved, but Sb migration increases due to film roughness
Solution Approach 1:
The buffer layer serves as a protective intermediary that prevents Sb migration during thermal annealing processes. It stabilizes the BiSb layer and prevents roughness-induced Sb diffusion, allowing thermal annealing to be applied successfully to achieve desired crystal orientation without the harmful side effect of Sb migration.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design improves field sensing and signal-to-noise ratio by reducing shield-to-shield spacing and enhancing current flow, leading to improved performance in magnetic recording heads.
Implementation Method 1
BiSb layers are narrow band gap topological insulators with both giant spin Hall effect and high electrical conductivity
Data Source
AI summary
The present disclosure generally relates to spin-orbit torque (SOT) devices comprising a bismuth antimony (BiSb) layer. The SOT devices further comprises a first shield, a BiSb layer disposed over the first shield (S1), a free layer (FL) disposed over the BiSb layer, and a second shield (S2) disposed over the FL. The S1, the FL, and the S2 are disposed at a media facing surface (MFS). The BiSb layer is recessed from the MFS a first distance of about 5 nm to about 20 nm. The FL has a length greater than the first distance. A notch and/or an insulation layer is disposed adjacent to the BiSb layer at the MFS. Current may be configured to flow vertically through the S2 to the FL, and horizontally from the FL to the BiSb layer. Current may be configured to flow vertically through the S2 to the S1.