Tetragonal Heusler MRAM Stack for High TMR and Low Switching Current
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Solution Overview
Problem
Current magnetoresistive random-access memory (MRAM) devices face challenges in achieving high spin polarization and low switching current while maintaining perpendicular magnetic anisotropy, which is crucial for scaling to smaller sizes.
Innovation Solution
The use of tetragonal half metallic Heusler compounds with a templating layer having an alternating layer lattice structure, which induces perpendicular magnetic anisotropy and maintains high spin polarization, thereby reducing the switching current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ferromagnetic alloys of cobalt, iron, and boron are used for magnetic layers, then the device structure is simple and manufacturing is easier, but spin polarization is insufficient leading to low TMR ratio
Solution Approach 1:
The patent employs half-metallic Heusler compounds as composite intermetallic materials with specific stoichiometry (X2YZ or XYZ) to achieve high spin polarization. These compounds combine transition metals (Co, Fe, Mn) with main group elements (Sn, Sb, Bi) in ordered crystal structures, creating a composite material that provides both high TMR ratio and perpendicular magnetic anisotropy, resolving the contradiction between simple structure and high spin polarization
Solution Approach 2:
The patent changes the magnetic anisotropy parameter from in-plane to perpendicular orientation by selecting specific half-metallic Heusler compounds and controlling their crystal structure. This parameter change enables the magnetic moment to orient perpendicular to the film plane, achieving both high spin polarization and the desired magnetic configuration for scaled devices
2Length of moving object
If magnetic layer thickness is reduced for scaling to smaller sizes, then device size decreases, but maintaining perpendicular magnetic anisotropy becomes more difficult
Solution Approach 1:
The patent utilizes half-metallic Heusler compounds that inherently exhibit perpendicular magnetic anisotropy as a bulk property of the material, rather than relying on interface effects that dominate in thin films. This material parameter change allows perpendicular anisotropy to be maintained even as layer thickness is reduced for scaling, decoupling the size reduction from the loss of magnetic anisotropy
Solution Approach 2:
The ordered intermetallic structure of half-metallic Heusler compounds provides intrinsic perpendicular magnetic anisotropy that is robust against thickness reduction. The specific atomic ordering and electronic structure of these composite materials create a bulk property that maintains magnetic anisotropy even in thin film form, enabling reliable scaling
3Reliability
If high spin polarization is achieved through material selection, then TMR ratio increases, but switching current remains high
Solution Approach 1:
The patent changes the magnetization orientation parameter from in-plane to perpendicular orientation by using half-metallic Heusler compounds. This parameter change reduces the switching current requirement because perpendicular magnetization allows for more efficient spin transfer torque switching, while simultaneously maintaining high TMR ratio through the half-metallic electronic structure
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 results in MRAM devices with high spin polarization, leading to high tunnel magnetoresistance and a high ON/OFF ratio, while also achieving low switching currents, enabling scaling to smaller sizes.
Implementation Method 1
induces perpendicular magnetic anisotropy
Implementation Method 2
having a Heusler in-plane lattice constant that is different from an in-plane lattice constant in a cubic form of the half metallic Heusler material
Implementation Method 3
maintains high spin polarization
Implementation Method 4
leading to high tunnel magnetoresistance
Implementation Method 5
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)
Data Source
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AI summary
A magnetoresistive random-access memory cell includes a templating layer (1203). The templating layer includes a binary alloy having an alternating layer lattice structure. The cell further includes a half metallic Heusler layer (1205) including a half metallic Heusler material having a tetragonal lattice structure. The half metallic Heusler layer is located outward of the templating layer, and has a Heusler in-plane lattice constant that is different from an in-plane lattice constant in a cubic form of the half metallic Heusler material. A tunnel barrier (1209) is located outward of the half metallic Heusler layer, and a magnetic layer (1211) is located outward of the tunnel barrier.