Perpendicular Spin Transfer Torque Memory with Bilayer Free Layer
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Solution Overview
Problem
The scaling of features in integrated circuits poses challenges for the commercialization of perpendicular spin transfer torque memory (pSTTM) devices, particularly in reducing switching current without compromising tunnel magnetoresistance (TMR) and resistance-area (RA), which are essential for improving thermal stability and patterning at smaller feature sizes.
Innovation Solution
A pSTTM device with a multilayer stack that includes a fixed magnetic layer, a tunnel barrier, and a free layer with a stack of bilayers comprising non-magnetic and magnetic layers, where the non-magnetic layers reduce saturation magnetization and enhance perpendicular anisotropy, allowing for reduced switching current and improved thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the feature size is reduced to increase memory density, then the number of memory devices per chip increases, but the switching current increases and thermal stability deteriorates
Solution Approach 1:
The patent changes the magnetic anisotropy parameter from in-plane to perpendicular orientation by modifying the free layer structure. This is achieved by introducing specific material compositions (e.g., CoFeB, CoFe) and controlling their thicknesses to generate perpendicular magnetic anisotropy (PMA) through interface effects and magnetocrystalline anisotropy. The PMA enables stable magnetization at smaller dimensions
Solution Approach 2:
The patent employs composite multilayer structures combining magnetic layers (CoFeB, CoFe, CoPt) with non-magnetic spacer layers (Ru, Ta, Mo). These composite structures create perpendicular magnetic anisotropy through interface coupling and magnetoelastic effects, enabling reduced switching current while maintaining thermal stability at scaled dimensions
2Use of energy by moving object
If the switching current is reduced to improve energy efficiency, then energy consumption decreases, but the tunnel magnetoresistance and resistance-area product deteriorate
Solution Approach 1:
The patent applies local quality by creating distinct functional regions within the magnetic layers. The free layer contains specific material compositions (CoFeB, CoFe) with controlled thicknesses to generate perpendicular magnetic anisotropy at interfaces, while maintaining overall layer functionality. This localized property enhancement enables reduced switching current without compromising TMR
Solution Approach 2:
The patent modifies the magnetic anisotropy parameter from in-plane to perpendicular orientation by adjusting layer thicknesses and material compositions. This parameter change enables spin transfer torque to efficiently switch magnetization at lower currents while preserving the tunnel magnetoresistance ratio through optimized interface properties
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
The solution enhances perpendicular anisotropy and stability, enabling efficient energy and computational performance while maintaining low switching current, thus addressing the challenges of scaling and integration in pSTTM devices.
Implementation Method 1
The non-magnetic layers in the stack of bilayers have a combined thickness that is less than 15% of a combined thickness of the magnetic layers in the stack of bilayers. The free layer reduces a saturation magnetization of the free layer and increases perpendicular magnetic anisotropy.
Implementation Method 2
perpendicular spin transfer torque memory (pSTTM) devices with enhanced perpendicular anisotropy
Data Source
AI summary
A material layer stack for a pSTTM device includes a fixed magnetic layer, a tunnel barrier disposed above the fixed magnetic layer and a free layer disposed on the tunnel barrier. The free layer further includes a stack of bilayers where an uppermost bilayer is capped by a magnetic layer including iron and where each of the bilayers in the free layer includes a non-magnetic layer such as Tungsten, Molybdenum disposed on the magnetic layer. In an embodiment, the non-magnetic layers have a combined thickness that is less than 15% of a combined thickness of the magnetic layers in the stack of bilayers. A stack of bilayers including non-magnetic layers in the free layer can reduce the saturation magnetization of the material layer stack for the pSTTM device and subsequently increase the perpendicular magnetic anisotropy.