Magnetoresistive Stack with Dual Tunnel Barriers for MR Ratio
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Solution Overview
Problem
Existing spin-torque magnetoresistive memory elements face challenges in achieving a high magnetoresistance ratio (MR) while maintaining a low critical current density, which is essential for improving read signals and reducing write current requirements.
Innovation Solution
The proposed solution involves a spin-torque magnetoresistive memory element structure with a free layer positioned between first and second electrodes, where the first and second tunnel barriers form tunnel junctions with distinct magnetoresistance ratios and resistance-area products. This structure includes a ferromagnetic alloy with low Fe content and high B content for the first electrode, and a non-ferromagnetic material for the second electrode, along with a high-Fe interface region and non-ferromagnetic transition metal layers to enhance magnetoresistance and reduce spin-torque critical current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional MTJ structure with single tunnel barrier is used, then the manufacturing process is simple, but the magnetoresistance ratio is insufficient
Solution Approach 1:
The patent divides the single tunnel barrier into two separate tunnel barriers (first tunnel barrier and second tunnel barrier) positioned on opposite sides of the free magnetic layer. This segmentation allows each barrier to be independently optimized for magnetoresistance properties, achieving a higher overall magnetoresistance ratio while maintaining manufacturability through established thin-film deposition processes.
Solution Approach 2:
The patent employs composite material structures including ferromagnetic layers (CoFeB), non-magnetic spacer layers (Ru, Ta), and tunnel barrier layers (MgO) arranged in a specific sequence. The combination of these materials with different magnetic and resistive properties creates the desired high magnetoresistance ratio while controlling the critical current density through material selection and thickness optimization.
2Power
If the critical current density is reduced to lower write current, then the write current requirement decreases, but the magnetoresistance ratio may be compromised
Solution Approach 1:
The patent applies local quality by creating asymmetric tunnel barrier structures where the first and second tunnel barriers have different thicknesses and material compositions. This allows the region with the lower critical current density to be localized in specific areas while maintaining high magnetoresistance ratio in the overall structure through the combined effect of both barriers.
Solution Approach 2:
The patent optimizes parameters including tunnel barrier thickness (5-20 nm), ferromagnetic layer thickness (3-10 nm), and material composition ratios to achieve the desired balance between critical current density and magnetoresistance ratio. By carefully adjusting these parameters, the patent reduces write current requirements while preserving high read signal capability.
3Reliability
If dual-spin-filter structure with two tunnel barriers is implemented, then the magnetoresistance ratio improves, but the manufacturing complexity increases
Solution Approach 1:
The patent segments the tunnel barrier function into two independent layers that can be deposited using separate process steps. Each tunnel barrier is formed using standard atomic layer deposition or chemical vapor deposition techniques, allowing the dual-barrier structure to be manufactured with existing fabrication infrastructure without requiring entirely new manufacturing processes.
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 achieves a high magnetoresistance ratio and low critical current density, enabling improved read signals and reduced write current requirements, thereby enhancing the performance and efficiency of spin-torque magnetoresistive memory elements.
Implementation Method 1
The spin angular momentum carried by the spin-polarized tunneling current causes reversal of the free layer, with the final state (parallel or antiparallel) determined by the polarity of the current pulse.
Implementation Method 2
exhibits an electrical resistance that depends on the magnetic state of the device. Corresponding to the parallel and antiparallel magnetic states, the magnetic memory element has low and high electrical resistance states, respectively.
Data Source
AI summary
A magnetoresistive element (e.g., a spin-torque magnetoresistive memory element) includes a fixed magnetic layer, a free magnetic layer, having a high-iron alloy interface region located along a surface of the free magnetic layer, wherein the high-iron alloy interface region has at least 50% iron by atomic composition, and a first dielectric, disposed between the fixed magnetic layer and the free magnetic layer. The magnetoresistive element further includes a second dielectric, having a first surface that is in contact with the surface of the free magnetic layer, and an electrode, disposed between the second dielectric and a conductor. The electrode includes: (i) a non-ferromagnetic portion having a surface that is in contact with a second surface of the second dielectric, and (ii) a second portion having at least one ferromagnetic material disposed between the non-ferromagnetic portion of the electrode and the conductor.