Asymmetric Free Layer Boron Gradient for STT-MRAM Stability
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Solution Overview
Problem
Current spin transfer torque based magnetic memories face challenges in improving performance, particularly in achieving stable magnetic states and enhanced magnetoresistance for efficient switching and storage.
Innovation Solution
A magnetic junction configuration is introduced, comprising a pinned layer, a nonmagnetic spacer layer, an asymmetric free layer with varying boron content, and a perpendicular magnetic anisotropy inducing layer, allowing the free layer to be switchable between stable magnetic states using spin transfer torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional symmetric free layers are used in spin transfer torque memories, then the device structure is simple and manufacturing is easier, but the magnetoresistance is insufficient and switching stability is poor
Solution Approach 1:
The patent applies asymmetry by creating a free layer with different boron concentrations at its top and bottom interfaces. Specifically, the free layer includes a first boron concentration at its top interface with the tunnel barrier and a second boron concentration at its bottom interface with the nonmagnetic layer, where these concentrations differ. This asymmetric composition creates unequal interface properties that enhance spin transfer torque efficiency and improve switching stability, directly resolving the technical contradiction between reliability and structural simplicity.
Solution Approach 2:
The patent implements local quality by varying the boron concentration locally within the free layer rather than using a uniform composition. The free layer has a gradient or stepped boron concentration profile, with higher boron content at one interface and lower boron content at the other interface. This localized compositional variation optimizes the magnetic and transport properties at specific interfaces, enhancing overall device performance while maintaining a relatively simple overall structure.
2Reliability
If conventional magnetic junctions are used, then the device configuration is straightforward, but the magnetoresistance ratio is insufficient for efficient memory operation
Solution Approach 1:
The patent enhances magnetoresistance by introducing asymmetry into the free layer's boron concentration profile. The asymmetric boron distribution creates different interface states at the top and bottom of the free layer, which modifies the spin-dependent transport properties. This results in a significantly enhanced tunnel magnetoresistance ratio, improving the reliability of memory operation while adding only moderate structural complexity through controlled compositional variation.
Solution Approach 2:
The patent utilizes parameter changes by systematically varying the boron concentration parameter within the free layer. By adjusting the boron content at different interfaces (first boron concentration at top interface, second boron concentration at bottom interface), the patent optimizes the magnetic anisotropy, saturation magnetization, and spin scattering properties. These parameter variations directly control the magnetoresistance ratio and switching characteristics, resolving the contradiction between performance and complexity.
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 magnetoresistance and improves spin transfer based switching, leading to better performance and stability of magnetic memories.
Implementation Method 1
STT-MRAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction. A spin polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction.
Implementation Method 2
The differences in magnetic configurations correspond to different magnetoresistances and thus different logical states
Implementation Method 3
a perpendicular magnetic anisotropy (PMA) inducing layer. The free layer is between the nonmagnetic spacer layer and the PMA inducing layer
Data Source
AI summary
A magnetic junction usable in a magnetic device is described. The magnetic junction includes a pinned layer, a nonmagnetic spacer layer, an asymmetric free layer and a perpendicular magnetic anisotropy (PMA) inducing layer. The nonmagnetic spacer layer is between the pinned layer and the free layer. The free layer is between the nonmagnetic spacer layer and the PMA inducing layer. The asymmetric free layer includes a first ferromagnetic layer having a first boron content and a second ferromagnetic layer having a second boron content. The second boron content is less than the first boron content. The first boron content and the second boron content are each greater than zero atomic percent. The first and second ferromagnetic layers each contain at least one of Co and CoFe. The magnetic junction is configured such that the asymmetric free layer is switchable between stable magnetic states when a write current is passed through the magnetic junction.