Spin Hall Effect Assisted STT-MRAM Device Design
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Solution Overview
Problem
Conventional spin transfer torque magnetic random access memory (STT-MRAM) devices face limitations in efficiency due to the spin polarization of magnetic tunnel junctions (MTJs), which restrict the writing current, and combining spin hall effect (SHE) with MTJs is challenging due to different current paths and directions, resulting in lower storage density and complex circuitry.
Innovation Solution
A spin hall effect (SHE) assisted STT-MRAM device is designed by coupling a magnetic tunnel junction (MTJ) with a SHE material and a field effect transistor (FET), where the SHE material is misaligned from the FET, allowing a horizontally flowing current to generate spin current and inject torque into the free layer, reducing the critical switching current and increasing storage density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If spin transfer torque switching is used in conventional STT-MRAM devices, then magnetic switching can be achieved, but the efficiency is limited by the spin polarization of the MTJ which cannot exceed one, establishing a lower bound for writing current
Solution Approach 1:
The patent introduces a spin hall effect material as an intermediary component between the current path and the magnetic tunnel junction. This mediator generates spin current through the spin hall effect when charge current flows through it, and this spin current is then injected into the ferromagnetic electrode to achieve magnetic switching. The intermediary approach decouples the charge current path from the spin current injection path, allowing independent optimization of each function.
Solution Approach 2:
The patent changes the fundamental parameter of spin injection efficiency by utilizing the spin hall effect material's ability to generate spin current with efficiency greater than one. This parameter change is achieved by selecting materials with high spin hall angles and optimizing the geometric configuration, thereby breaking the conventional limit imposed by MTJ spin polarization and enabling lower writing currents.
2Productivity
If three terminal devices are used to combine SHE with MTJ, then spin hall effect torque can be generated, but more than one transistor per unit cell is required, resulting in lower storage density and more complex circuitry
Solution Approach 1:
The patent merges the spin hall effect material directly with the magnetic tunnel junction structure, integrating multiple functions into a unified component. The SHE material is positioned adjacent to the MTJ such that it shares common terminals and current paths, eliminating the need for separate three-terminal device structures. This merging reduces the transistor count per unit cell and simplifies the overall circuit architecture while maintaining the spin hall effect torque generation capability.
3Productivity
If three terminal devices are used to combine SHE with MTJ, then spin hall effect torque can be generated, but more than one transistor per unit cell is required, resulting in lower storage density
Solution Approach 1:
The patent merges the spin hall effect material directly with the magnetic tunnel junction structure, integrating multiple functions into a unified component. The SHE material is positioned adjacent to the MTJ such that it shares common terminals and current paths, eliminating the need for separate three-terminal device structures. This merging reduces the transistor count per unit cell and simplifies the overall circuit architecture while maintaining the spin hall effect torque generation capability.
Solution Approach 2:
The patent utilizes spatial reconfiguration by positioning the spin hall effect material in a lateral dimension adjacent to the MTJ rather than requiring additional vertical stacking or separate terminal structures. This dimensional arrangement allows the SHE material to generate torque while sharing the same current path, effectively reducing the area required per storage bit and improving storage density.
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 SHE assisted STT-MRAM achieves a significant reduction in critical switching current, enhances storage density, and improves switching speed while being energy efficient, with the spin torque from the SHE being more than ten times larger than the tunneling current torque, and the critical current being more than ten times smaller than conventional MTJs.
Implementation Method 1
The spin hall effect (SHE) may be used to generate spin current. SHE may be used as an alternative to using a spin filtering effect inside a MTJ. Using SHE, a spin current is generated in a transverse direction while a charge current flows in a longitudinal direction.
Implementation Method 2
In a typical spin transfer torque magnetic random access memory (STT-MRAM) device that is composed of a magnetic tunnel junction (MTJ) and a field effect transistor (FET), the efficiency of the spin transfer torque switching is limited by the spin polarization of the MTJ
Data Source
AI summary
Embodiments are directed to providing a spin hall effect (SHE) assisted spin transfer torque magnetic random access memory (STT-MRAM) device by coupling a magnetic tunnel junction (MTJ) to a SHE material, and coupling the SHE material to a transistor. Embodiments are directed to a spin transfer torque magnetic random access memory (STT-MRAM) device comprising: a magnetic tunnel junction (MTJ) coupled to a spin hall effect (SHE) material, and a transistor coupled to the SHE material.