Heusler Alloy Buffer Layers for BiSb SOT Devices
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Solution Overview
Problem
Bismuth antimony (BiSb) materials face challenges in commercial spin-orbit torque (SOT) applications due to low melting points, large grain sizes, significant Sb migration issues, film roughness, and difficulty in maintaining desired crystal orientations, which affect the spin Hall effect and durability of SOT devices.
Innovation Solution
The use of a spin-orbit torque device comprising a BiSb layer with a nonmagnetic buffer layer, interlayer, and barrier layer, where one or more of these layers comprise a polycrystalline non-Heusler alloy material or Heusler alloy, selected from specific elements like Cu, Ag, Ge, Mn, Ni, Co, Mo, W, Sn, and In, to enhance crystal orientation and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If BiSb materials are used in SOT devices, then giant spin Hall effect and high electrical conductivity are achieved, but low melting points and large grain sizes cause significant Sb migration and film roughness
Solution Approach 1:
A buffer layer comprising a Heusler alloy is introduced between the substrate and the BiSb layer. This intermediary layer serves as a migration barrier that prevents Sb atoms from diffusing into the substrate while maintaining the desired (012) crystal orientation of the BiSb layer, thus resolving the contradiction between achieving giant spin Hall effect and preventing Sb migration
Solution Approach 2:
The patent employs a composite structure combining Heusler alloy buffer layer with BiSb layer. The Heusler alloy (comprising elements like Co, Mn, Fe, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, Au combined with Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Hf, W, B, Al, Si, Ga, Ge, As, In, Sn, Sb, Bi) provides both structural support for orientation maintenance and chemical barrier properties to prevent Sb migration, simultaneously enabling the BiSb layer to exhibit its giant spin Hall effect
2Reliability
If BiSb materials are used to achieve desired crystal orientation, then maximum spin Hall effect is obtained, but difficulty maintaining (012) or (001) orientation occurs
Solution Approach 1:
The Heusler alloy buffer layer is deposited beforehand to establish a crystalline template with the desired (012) or (001) orientation. This preliminary structural preparation provides a oriented seed crystal structure that guides the subsequent BiSb layer to grow with the desired crystal orientation, making the orientation maintenance achievable and reproducible
Solution Approach 2:
The patent utilizes the specific crystallographic parameters and lattice structure of the Heusler alloy to control the orientation of the BiSb layer. By selecting appropriate Heusler alloy compositions and thicknesses, the crystal orientation of the BiSb layer is precisely controlled to achieve maximum spin Hall effect while maintaining manufacturing feasibility
3Reliability
If BiSb materials are used for SOT applications, then high electrical conductivity is achieved, but softness and ease of damage by ion milling occur
Solution Approach 1:
The Heusler alloy buffer layer acts as a protective intermediary that shields the soft BiSb layer from direct damage during ion milling processes. The buffer layer absorbs the mechanical stress and ion bombardment, preventing damage to the underlying BiSb layer while maintaining its high electrical conductivity properties
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
This configuration improves the signal-to-noise ratio and maintains a strong (012) or (001) crystal orientation for the BiSb layer, leading to enhanced spin Hall effect and electrical conductivity, thus improving the performance and reliability of SOT devices in applications like magnetic recording heads and MRAM devices.
Implementation Method 1
BiSb layers are narrow band gap topological insulators with both giant spin Hall effect and high electrical conductivity
Implementation Method 2
maintaining a desired (012) or (001) orientation for maximum spin Hall effect
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 nonmagnetic buffer layer, a nonmagnetic interlayer, a ferromagnetic layer, and a nonmagnetic barrier layer. One or more of the barrier layer, interlayer, and buffer layer comprise a polycrystalline non-Heusler alloy material, or a Heusler alloy and a material selected from the group consisting of: Cu, Ag, Ge, Mn, Ni, Co, Mo, W, Sn, B, and In. The Heusler alloy is a full Heusler alloy comprising X2YZ or a half Heusler alloy comprising XYZ, where X is one of: Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au, Y is one of: Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Y, Zr, Nb, Mo, Hf, and W, and Z is one of: B, Al, Si, Ga, Ge, As, In, Sn, Sb, and Bi.