W-X Alloy Magnetic Tunnel Junction for Stable PMA After Annealing
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Solution Overview
Problem
Existing magnetic tunnel junctions face challenges in maintaining perpendicular magnetic anisotropy (PMA) and achieving high spin-orbit torque efficiency at low resistivity, particularly after heat treatment, which is crucial for efficient spin-orbit torque (SOT) switching in magnetic random access memory (MRAM).
Innovation Solution
A spin-orbit torque-based magnetic tunnel junction using a W-X alloy, where X includes group IV semiconductors and group III-V semiconductors, as the spin-orbit torque active layer, which maintains PMA and achieves high spin-orbit torque efficiency at low resistivity, with a tungsten-titanium alloy being preferred, and a method of manufacturing this junction involving specific heat treatment and composition control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional W or Ta spin-orbit torque active layer is used, then the structure is simple, but the spin-orbit torque efficiency is insufficient and PMA cannot be maintained after heat treatment
Solution Approach 1:
The patent employs W-X alloy composite materials where W is tungsten and X is a group IV semiconductor (Si, Ge, Sn) or group III-V semiconductor (GaAs, InAs, InSb). This composite approach combines the beneficial properties of tungsten (high spin Hall angle) with semiconductor elements (lattice matching capability and thermal stability), enabling the structure to maintain perpendicular magnetic anisotropy after heat treatment while achieving high spin-orbit torque efficiency.
Solution Approach 2:
The patent systematically varies the composition parameter X in the W-X alloy to optimize performance. By controlling the atomic percentage of the semiconductor element (e.g., 1-20 at% for group IV semiconductors), the patent achieves optimal balance between spin-orbit torque efficiency, resistivity, and PMA stability after heat treatment, transforming a single-material system into a tunable compositional space.
2Use of energy by moving object
If the spin-orbit torque active layer resistivity is reduced, then the switching current decreases, but the spin Hall angle and spin-orbit torque efficiency deteriorate
Solution Approach 1:
The patent utilizes compositional parameter changes in the W-X alloy to independently control resistivity and spin Hall angle. By adjusting the semiconductor element concentration, the patent achieves low resistivity (improving switching current) while maintaining or enhancing spin-orbit torque efficiency, breaking the traditional inverse relationship between these parameters.
Solution Approach 2:
The W-X composite alloy structure enables decoupling of electrical and spin transport properties. The tungsten component provides high spin Hall angle while the semiconductor component controls resistivity through band structure engineering, allowing simultaneous optimization of both switching current and spin-orbit torque efficiency.
3Reliability
If heat treatment is applied to maintain PMA, then the magnetic anisotropy is improved, but the alloy composition and structure may deteriorate
Solution Approach 1:
The W-X alloy composite structure exhibits enhanced thermal stability compared to pure W or Ta. The semiconductor elements form thermally stable interfacial compounds with the magnetic layers, maintaining the perpendicular magnetic anisotropy even after high-temperature heat treatment (e.g., 300-400°C), while the alloy composition remains stable without excessive interdiffusion or phase separation.
Solution Approach 2:
The patent creates local quality variations at the interfaces between the W-X alloy and adjacent magnetic layers. The semiconductor elements preferentially segregate at interfaces, forming localized regions with enhanced thermal stability and chemical bonding, which anchor the perpendicular magnetic anisotropy during heat treatment without requiring bulk compositional changes.
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 W-X alloy-based magnetic tunnel junction maintains PMA even after heat treatment, reduces switching current, and enhances spin-orbit torque efficiency, making it suitable for high-speed, low-power SOT switching in MRAM.
Implementation Method 1
the spin-orbit torque (SOT) phenomenon that induces switching of a magnetization-free layer using the spin Hall effect or the Rashba effect occurring when current flows in a parallel direction in a plane of a spin-orbit active layer adjacent to the magnetization-free layer
Implementation Method 2
The magnetic tunnel junction reads information using the tunneling magnetoresistance (TMR) phenomenon that an electrical resistance value of a tunneling current passing through an insulating layer changes depending on the relative magnetization directions of the magnetization-free layer and the pinned layer
Implementation Method 3
a W-X alloy thin film (where W is tungsten, and X includes at least one of group IV semiconductors and group III-V semiconductors) having large spin-orbit coupling as a spin-orbit torque active layer
Data Source
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AI summary
Disclosed is a spin-orbit torque (SOT)-based magnetic tunnel junction, including: a spin-orbit torque active layer formed on a substrate; a magnetization-free layer formed on the spin-orbit torque active layer; a tunnel barrier layer formed on the free magnetic layer; and a magnetization-pinned layer formed on the tunnel barrier layer, wherein the spin-orbit torque active layer is a W-X alloy (where W is tungsten, and X includes at least one of Ti, Zr and Hf or a group III-V semiconductor).