Symmetry Filter Magnetic Junction for STT-RAM Critical Current Reduction
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Solution Overview
Problem
Conventional magnetic junctions in STT-RAMs face challenges in achieving higher density, lower critical current, and simpler fabrication methods while maintaining performance, particularly in optimizing the critical current for thermally stable free layers.
Innovation Solution
The introduction of a symmetry filter layer between the free and pinned layers, which preferentially transmits charge carriers with specific symmetry, enhancing spin polarization and reducing the critical current by configuring the layers to have charge carriers of the desired symmetry at the Fermi level in one spin channel and lacking them in another, with magnetic moments perpendicular to the plane.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional magnetic junctions are used with CoFe and CoFeB layers and MgO tunneling barrier, then the critical current is reduced, but the device density and scalability are limited
Solution Approach 1:
The patent introduces a symmetry filter layer that asymmetrically filters charge carriers based on their symmetry properties. This creates an asymmetric transmission probability for different spin channels, enhancing spin polarization efficiency and reducing critical current while enabling higher device density through improved spin torque effectiveness
Solution Approach 2:
The symmetry filter layer acts as an intermediary between the pinned layer and free layer. It mediates the spin transport by preferentially transmitting charge carriers with specific symmetry, thereby enhancing the spin polarization of current passing through the magnetic junction and reducing the critical current required for switching
2Reliability
If the free layer is made thermally stable with high energy barrier, then data retention is improved, but the critical current for switching increases
Solution Approach 1:
The patent changes the symmetry parameter of charge carriers by introducing the symmetry filter layer. This parameter change enhances spin polarization efficiency, allowing thermally stable free layers to be switched at lower critical currents by improving the effectiveness of spin torque rather than increasing the current magnitude
3Ease of operation
If conventional current-perpendicular-to-plane switching is used, then the magnetic moment switching is achieved, but the spin polarization efficiency is insufficient for high density applications
Solution Approach 1:
The symmetry filter layer serves as an intermediary that enhances spin polarization efficiency by preferentially transmitting charge carriers with specific symmetry. This intermediary layer improves the quality of spin-polarized current without complicating the current-perpendicular-to-plane switching operation
Solution Approach 2:
The symmetry filter layer introduces local quality enhancement at the interface between the pinned and free layers. By creating a region with enhanced spin polarization properties, the overall spin torque effectiveness is improved while maintaining the simplicity of conventional switching operation
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 spin polarization efficiency and reduces the critical current, leading to enhanced performance and scalability of magnetic junctions for higher density STT-RAMs.
Implementation Method 1
enhancing spin polarization by configuring the layers to have charge carriers of the desired symmetry at the Fermi level
Implementation Method 2
The symmetry filter transmits charge carriers having a first symmetry with higher probability than charge carriers having another symmetry
Implementation Method 3
STT-RAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction
Implementation Method 4
Current passing through the conventional pinned layer 30 becomes spin polarized and carries angular momentum. This angular momentum may be transferred to the conventional free layer 50
Implementation Method 5
magnetic tunneling junctions usable in spin transfer torque magnetic memories
Data Source
AI summary
A method and system for providing a magnetic junction are described. The method and system include providing a free layer, a symmetry filter, and a pinned layer. The free layer has a first magnetic moment switchable between stable states when a write current is passed through the magnetic junction. The symmetry filter transmits charge carriers having a first symmetry with higher probability than charge carriers having another symmetry. The pinned layer has a second magnetic moment pinned in a direction. The symmetry filter resides between the free layer and the pinned layer. At least one of the free layer and the pinned layer lies in a plane, has the charge carriers of the first symmetry in a spin channel at a Fermi level, lacks the charge carriers of the first symmetry at the Fermi level in another spin channel, and has a nonzero magnetic moment component perpendicular to the plane.