Rare Earth Magnetic Junctions for STT-MRAM Thermal Stability
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Solution Overview
Problem
Current spin transfer torque random access memories (STT-MRAMs) face challenges in achieving high perpendicular magnetic anisotropy and thermal stability, which are crucial for improved performance and endurance.
Innovation Solution
A magnetic junction design is introduced, featuring a free layer and a pinned layer with a nonmagnetic spacer, where both layers include multilayers with a bilayer structure comprising a magnetic transition metal alloy and a rare earth alloy, providing high perpendicular magnetic anisotropy and thermal robustness up to 400 degrees Celsius.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional magnetic layers are used in STT-MRAM, then the device structure is simple, but the perpendicular magnetic anisotropy is insufficient and thermal stability is poor
Solution Approach 1:
The patent employs composite multilayer structures combining magnetic layers (CoFeB, CoFe) with nonmagnetic spacer layers (Ru, Ta) and rare earth layers (Tb) to achieve high perpendicular magnetic anisotropy and thermal stability. The composite nature of these multilayers provides both the required magnetic properties and structural complexity to maintain stability up to 400°C annealing temperatures.
2Reliability
If higher anneal temperatures are used to improve thermal stability, then thermal stability increases, but the magnetic layer properties may deteriorate
Solution Approach 1:
The patent optimizes specific parameters including layer thicknesses (e.g., 3-5 nm for magnetic layers, 0.5-2 nm for spacers), material compositions (CoFeB with 20-30 at% B, CoFe with specific Co:Fe ratios), and annealing temperatures (up to 400°C) to achieve the desired balance between thermal stability and compositional integrity. These parameter optimizations enable the magnetic layers to withstand high-temperature processing.
3Productivity
If the perpendicular magnetic anisotropy is increased to improve switching performance, then write/switching efficiency improves, but the thermal robustness decreases
Solution Approach 1:
The patent achieves dynamic balance between perpendicular magnetic anisotropy and thermal robustness through carefully engineered multilayer configurations. The system can exhibit high PMA at operating temperatures for efficient switching while maintaining thermal robustness through the stabilizing effect of the multilayer structure and interfacial engineering, allowing the magnetic properties to be optimized for both speed and stability.
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 design enhances the magnetic and electrical properties of the junction, leading to improved thermal stability and performance, allowing for higher anneal temperatures and increased tunneling magnetoresistance, thus improving the overall performance of STT-MRAMs.
Implementation Method 1
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
Data Source
AI summary
A magnetic junction usable in a magnetic device and a method for providing the magnetic junction are described. The magnetic junction includes a free layer, a pinned layer and nonmagnetic spacer layer between the free and pinned layers. The free layer is switchable between stable magnetic states when a write current is passed through the magnetic junction. The free and pinned layers each has a layer perpendicular magnetic anisotropy energy greater than an out-of-plane demagnetization energy. At least one of the pinned layer and the free layer includes a multilayer. The multilayer includes at least one bilayer. Each of the bilayer(s) has a first layer and a second layer. The first layer includes an alloy of a magnetic transition metal and a rare earth. The second layer includes an amorphous magnetic layer. The multilayer has a nonzero perpendicular magnetic anisotropy up to at least four hundred degrees Celsius.