BiSb SOT Electrode Crystallization for Low-Current MRAM Switching
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Solution Overview
Problem
Existing magnetoresistive devices face challenges in increasing the spin Hall angle for efficient conversion of current to spin current, leading to high switching currents in spin-orbit torque (SOT) magnetoresistive memory.
Innovation Solution
Incorporating a BiSb SOT electrode with a (012) crystal orientation, utilizing a buffer layer of oxide, nitride, or oxynitride to promote this orientation, and employing a manufacturing process involving sputtering, planarization, and annealing to achieve a smooth and conductive SOT electrode layer with a spin Hall angle of 5 or more.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional SOT electrode material (W or Ta) is used, then the device structure is simple, but the spin Hall angle is low resulting in high switching current
Solution Approach 1:
The patent changes the material composition parameter from conventional W or Ta to BiSb alloy, and controls the crystal orientation parameter to achieve (012) orientation. This parameter change increases the spin Hall angle from typical values of 0.5-0.8 for W/Ta to 0.9 or higher for BiSb with (012) orientation, thereby reducing the switching current while maintaining manufacturing feasibility through established sputtering techniques
Solution Approach 2:
The patent uses a composite structure consisting of BiSb alloy with specific composition ratios (Bi:Sb = 95:5 to 80:20 atomic ratio) combined with a buffer layer having (012) crystal orientation. This composite material system achieves both high spin Hall angle and controlled crystal orientation, resolving the contradiction between performance improvement and manufacturing complexity
2Use of energy by moving object
If BiSb material is used to increase spin Hall angle, then switching current is reduced, but surface roughness increases affecting device performance
Solution Approach 1:
The patent introduces a buffer layer as an intermediary between the substrate and the BiSb SOT electrode layer. This buffer layer has (012) crystal orientation that promotes epitaxial growth of the BiSb layer, enabling the achievement of smooth surface (Ra ≤ 0.5 nm) while maintaining the high spin Hall angle properties of BiSb material
Solution Approach 2:
The patent controls the surface roughness parameter by optimizing the sputtering conditions and using a buffer layer with specific crystal orientation. The arithmetic average roughness is controlled to be 0.5 nm or less, which maintains good interface contact and electrical properties while preserving the high spin Hall angle of the BiSb material
3Use of energy by moving object
If BiSb SOT electrode with (012) orientation is used, then spin Hall angle increases significantly, but manufacturing process complexity increases
Solution Approach 1:
The patent performs preliminary action by forming a buffer layer with (012) crystal orientation before depositing the BiSb SOT electrode layer. This preliminary preparation of the buffer layer with specific crystal orientation enables the subsequent BiSb layer to inherit and maintain the (012) orientation, achieving high spin Hall angle through a systematic multi-step process rather than attempting to directly control BiSb crystallization
Solution Approach 2:
The buffer layer serves as an intermediary that mediates between the substrate and the BiSb layer, providing the necessary crystal orientation template. This intermediary layer simplifies the manufacturing process by decoupling the complex task of controlling BiSb crystal orientation from the deposition process itself, making the overall manufacturing more manageable while achieving the desired high spin Hall angle
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 solution enhances the spin Hall angle and reduces switching currents, resulting in improved power efficiency and performance of magnetoresistive devices.
Implementation Method 1
a value of the spin Hall angle, which is the conversion efficiency from electric current to spin current, may be about 5 or more
Implementation Method 2
forming a sputtered film by sputtering a material containing BiSb on the buffer layer
Implementation Method 3
promoting crystallization of the SOT electrode layer by annealing the SOT electrode layer at a temperature greater than a melting point of BiSb and then cooling the SOT electrode layer
Implementation Method 4
annealing the SOT electrode layer at a temperature greater than a melting point of BiSb
Data Source
AI summary
A method of manufacturing a magnetoresistive device includes: forming a spin-orbit torque (SOT) electrode layer that applies SOT to a first magnetic layer of a magnetic tunnel junction device by flowing current on a buffer layer, wherein the forming of the SOT electrode layer includes forming a sputtered film by sputtering a material containing BiSb on the buffer layer and forming a planarized sputtered film after planarizing the sputtered film by a surface planarization process, forming an intermediate layer on the SOT electrode layer, promoting crystallization of the SOT electrode layer by annealing the SOT electrode layer at a temperature greater than a melting point of BiSb and then cooling the SOT electrode layer, and forming a magnetic tunnel junction device on the intermediate layer, the magnetic tunnel junction device including a first magnetic layer, a non-magnetic layer, and a second magnetic layer formed on the non-magnetic layer.