Heusler Film Material Stack for Lower MRAM Switching Current
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Solution Overview
Problem
Current MRAM devices using cobalt, iron, and boron alloys for magnetic layers face challenges in scaling to smaller sizes due to high switching currents and thermal instability, while Heusler compounds with volume anisotropy offer lower switching currents but require complex material stacks.
Innovation Solution
Incorporation of a sub-monolayer nitride layer and a binary alloy templating layer with an alternating lattice structure to facilitate the growth of Heusler compounds with perpendicular magnetic anisotropy, reducing grain boundaries and spin pumping effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cobalt, iron, and boron alloys are used for magnetic layers, then ferromagnetic properties are achieved, but switching current increases and thermal stability deteriorates when scaling to smaller sizes
Solution Approach 1:
The patent changes the magnetic anisotropy parameter from in-plane to perpendicular magnetization by modifying the material composition and interface structure. This is achieved through introducing heavy metal layers (Pt, Ir, Au) that induce perpendicular magnetic anisotropy at the interface, thereby reducing switching current while improving thermal stability in scaled devices
Solution Approach 2:
The patent employs composite material structures combining magnetic layers (CoFeB, CoFe) with non-magnetic spacer layers (Ru, Rh, Ir) and heavy metal layers (Pt, Au). These composite structures leverage spin-orbit coupling at the interfaces to reduce damping and switching current while maintaining thermal stability through controlled layer thicknesses and material properties
2Use of energy by moving object
If Heusler compounds with volume anisotropy are used, then lower switching currents are achieved, but device complexity increases due to required complex material stacks
Solution Approach 1:
The patent applies local quality by introducing perpendicular magnetic anisotropy only at specific interfaces between magnetic layers and heavy metal layers, rather than requiring bulk volume anisotropy throughout the entire magnetic layer. This localized approach at the interface reduces the complexity of the overall material stack while achieving low switching currents
Solution Approach 2:
The patent uses heavy metal layers (Pt, Ir, Au) as intermediary layers between the magnetic layers and the substrate or other magnetic layers. These intermediary layers mediate the magnetic coupling and induce perpendicular anisotropy through spin-orbit coupling, simplifying the overall stack design compared to using complex Heusler compounds with volume anisotropy
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 improved switching performance, lower switching currents, and enhanced thermal stability of MRAM devices by utilizing Heusler compounds with volume anisotropy, achieving higher efficiency and reduced power consumption.
Implementation Method 1
an ultra-thin templating layer, outward of the resistive layer. The ultra-thin templating layer includes a binary alloy having an alternating layer lattice structure
Implementation Method 2
A Heusler layer is located outward of the ultra-thin templating layer, includes a Heusler compound, and exhibits perpendicular magnetic anisotropy (PMA)
Implementation Method 3
Incorporation of a sub-monolayer nitride layer and a binary alloy templating layer with an alternating lattice structure to facilitate the growth of Heusler compounds with perpendicular magnetic anisotropy, reducing grain boundaries and spin pumping effects
Implementation Method 4
The magnetic state of one of the layers is switched using Spin Transfer Torque (STT). Thus, current MRAMs are three-layer devices employing a magnetic tunnel junction (MTJ). 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)
Implementation Method 5
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
Data Source
AI summary
A magnetoresistive random-access memory cell includes a substrate; a seed layer outward of the substrate; a resistive layer outward of the seed layer; and an ultra-thin templating layer. The ultra-thin templating layer is outward of the resistive layer, and includes a binary alloy having an alternating layer lattice structure. The ultra-thin templating layer has a thickness of 7-30 Angstroms. A Heusler layer is located outward of the ultra-thin templating layer, includes a Heusler compound, and exhibits perpendicular magnetic anisotropy (PMA).