Perpendicular Magnetic Tunneling Junctions for Low Critical Current STT-RAM
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Solution Overview
Problem
Conventional magnetic tunneling junctions in spin transfer torque random access memories (STT-RAMs) face challenges in achieving higher density, lower critical current, and simpler fabrication methods while maintaining performance.
Innovation Solution
A magnetic junction system comprising a free layer, a symmetry filter, and a pinned layer, where the symmetry filter transmits charge carriers with specific symmetry with higher probability, and at least one of the layers has a nonzero magnetic moment component perpendicular to the plane, with lattice mismatch less than seven percent, using materials like Ge, GaAs, and ZnSe.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional magnetic tunneling junctions are used in STT-RAM, then the basic memory function is achieved, but the critical current is too high and density is limited
Solution Approach 1:
The patent changes the magnetic moment orientation parameter from in-plane to perpendicular-to-plane configuration. This parameter change fundamentally alters the spin transport mechanism, enabling spin polarization without requiring high current densities, thus reducing critical current while allowing higher memory density
Solution Approach 2:
The patent employs composite material structures including CoFeB (cobalt ferrite boride) for the magnetic layers and MgO (magnetite oxide) for the tunnel barrier. These composite materials provide enhanced spin polarization efficiency and perpendicular magnetic anisotropy, enabling lower critical current operation
2Use of energy by moving object
If CoFe and CoFeB materials are used with MgO tunnel barrier, then critical current is reduced, but manufacturing complexity increases
Solution Approach 1:
The patent optimizes the thickness parameters of CoFeB layers and MgO barrier to specific ranges that simultaneously achieve low critical current and compatibility with standard fabrication processes. The perpendicular magnetic anisotropy is engineered through controlled layer thicknesses rather than complex material compositions
Solution Approach 2:
The patent uses CoFeB material which provides homogeneous magnetic properties and perpendicular magnetic anisotropy throughout the layer, simplifying fabrication compared to multi-layer composite structures. The uniform material composition reduces manufacturing variability while maintaining low critical current
3Reliability
If in-plane magnetic moments are used in conventional junctions, then fabrication is simpler, but spin polarization efficiency is insufficient
Solution Approach 1:
The patent introduces perpendicular magnetic anisotropy which creates asymmetric spin transport properties. The perpendicular magnetic moment configuration breaks the symmetry of conventional in-plane structures, enabling enhanced spin polarization efficiency through spin-orbit coupling mechanisms
Solution Approach 2:
The patent changes the magnetic moment orientation parameter from in-plane to perpendicular-to-plane configuration. This parameter change fundamentally alters the spin transport mechanism, enabling spin polarization without requiring high current densities, thus reducing critical current while allowing higher memory 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
This configuration enhances spin polarization efficiency, reduces the critical current, and improves the performance of magnetic memories by allowing for higher density and simpler fabrication.
Implementation Method 1
The symmetry filter transmits charge carriers having a first symmetry with higher probability than charge carriers having another symmetry. At least one of the free layer and the pinned layer has the charge carriers of the first symmetry in a spin channel at the Fermi level
Implementation Method 2
STT-RAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction. 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 3
The magnetic moment 32 of the conventional pinned layer 30 is fixed by an interaction with the conventional AFM layer 20
Implementation Method 4
If a sufficient amount of angular momentum is so transferred, the magnetic moment 52 of the free layer 50 may be switched to be parallel or antiparallel to the magnetic moment 32 of the pinned layer 30
Data Source
AI summary
A method and system provide a magnetic junction. A free layer, a symmetry filter, and a pinned layer are provided. The free layer has a 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 symmetry filter resides between the free layer and the pinned layer. The free layer and/or 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. The free layer and/or the pinned layer and the symmetry filter has at least one lattice mismatch of less than seven percent.