Heusler STT-MTJ Structure for High TMR and Low Switching Current
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Solution Overview
Problem
Current magnetic random access memory (MRAM) devices using magnetic tunnel junctions (MTJs) face challenges in achieving high tunnel magnetoresistance (TMR) and low switching current, which are essential for efficient neuromorphic computing.
Innovation Solution
The development of neuromorphic computing arrays utilizing Heusler alloy-based spin-transfer-torque magnetic tunnel junctions (STT-MTJs) with a specific layered structure, including a substrate, seed layer, nitride layer, templating layer, magnetic layer with Heusler compound exhibiting perpendicular magnetic anisotropy (PMA), tunnel barrier, and additional magnetic layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional magnetic tunnel junctions with ferromagnetic layers are used, then the device structure is simple, but the tunnel magnetoresistance is insufficient and switching current is high
Solution Approach 1:
The patent employs Heusler alloy compounds (such as Co2MnSi, Co2FeAl) as magnetic layers in the magnetic tunnel junction, replacing conventional ferromagnetic materials. These composite intermetallic materials provide enhanced spin polarization and perpendicular magnetic anisotropy, achieving high TMR ratios while maintaining a manageable layered structure with substrate, seed layer, templating layer, magnetic layer, tunnel barrier, and capping layer.
Solution Approach 2:
The patent utilizes perpendicular magnetic anisotropy (PMA) instead of in-plane magnetization by changing the magnetic orientation parameter. This parameter change in the Heusler alloy magnetic layer enables smaller switching currents while maintaining high TMR, resolving the contradiction between reliability and device complexity.
2Use of energy by moving object
If perpendicular magnetic anisotropy is implemented to reduce switching current, then switching current decreases, but the device requires precise layer thickness control and specific material composition
Solution Approach 1:
The patent changes the magnetic anisotropy parameter from in-plane to perpendicular orientation by selecting Heusler alloy materials with specific crystal structures. This parameter change inherently provides PMA, reducing switching current while the standardized layered structure with controlled thickness ranges (e.g., tunnel barrier 2-10 nm, magnetic layer 3-20 nm) establishes manufacturable precision requirements.
Solution Approach 2:
The patent introduces templating layers (such as oxide layers or metallic underlayers) as intermediary structures between the substrate and Heusler alloy magnetic layer. These intermediary layers facilitate the formation of perpendicular magnetic anisotropy and enable precise control of magnetic properties without requiring extreme manufacturing precision in the magnetic layer itself.
3Productivity
If Heusler alloy-based magnetic tunnel junctions are used to achieve high TMR and low switching current, then neuromorphic computing performance improves, but the fabrication process becomes more complex
Solution Approach 1:
The patent segments the magnetic tunnel junction into distinct functional layers: substrate, seed layer, templating layer, Heusler alloy magnetic layer, tunnel barrier, and capping layer. This segmentation allows each layer to be optimized independently for its specific function while using established thin-film deposition techniques, making the fabrication process more manageable despite the increased overall complexity.
Solution Approach 2:
The Heusler alloy magnetic layer serves multiple functions simultaneously: it provides perpendicular magnetic anisotropy for low switching current, exhibits high spin polarization for high TMR, and enables multi-state operations for neuromorphic computing. This multi-functionality reduces the need for additional specialized layers, simplifying the overall fabrication process while maintaining high neuromorphic computing efficiency.
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 approach enables the creation of MRAM devices with improved TMR and reduced switching current, facilitating efficient neuromorphic computing by allowing for multi-state operations and compatible switching times with neuromorphic time scales.
Implementation Method 1
a magnetic layer overlying the templating layer, the magnetic layer including a Heusler compound and exhibiting perpendicular magnetic anisotropy (PMA)
Implementation Method 2
The magnetic state of one of the layers is switched using Spin Transfer Torque (STT). Current is passed through the device and the resistance is measured. The current delivers spin angular momentum, so that once a threshold current is exceeded, the direction of the memory layer moment is switched.
Implementation Method 3
The resistance changes based on the magnetic orientation of the two magnetic layers, and the relative change in resistance is referred to as the tunnel magnetoresistance (TMR), which is related to the spin polarization (i.e., high spin polarization implies high TMR).
Data Source
AI summary
A neuromorphic computing array includes horizontal lines and vertical lines that intersect the horizontal lines at cell locations. Magnetic tunnel junction cells are located at the cell locations. Each cell is electrically connected to a corresponding one of the horizontal lines and to a corresponding one of the vertical lines. Each cell includes a substrate, a seed layer overlying the substrate, and a nitride layer, overlying the seed layer, and optionally having a thickness greater than 5 Angstroms. Each cell further includes a templating layer, outward of the nitride layer, including a binary alloy having an alternating layer lattice structure, and having a thickness greater than 50 Angstroms. Each cell still further includes a magnetic layer overlying the templating layer, a tunnel barrier outward of the magnetic layer; and a magnetic layer outward of the tunnel barrier. The magnetic layer includes a Heusler compound and exhibits perpendicular magnetic anisotropy (PMA).