STT-MRAM Free Layer Boron Gradient for Stiffness
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Solution Overview
Problem
Magnetic tunnel junctions (MTJs) face a high threshold voltage or current requirement to switch the free layer magnetization due to low internal stiffness, hindering practical applications in spin torque transfer-based magnetic memory elements.
Innovation Solution
A spin transfer torque magnetic random access memory (STTMRAM) element with a free layer structure is developed, where a first free sub-layer is deposited and annealed to reduce boron content at the interface, followed by cooling and depositing additional free sub-layers with varying boron content to enhance internal stiffness through a multi-step annealing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a CoFeB free layer is annealed to form distinct CoFe and CoFeB layers, then the layer structure is optimized, but the internal stiffness decreases and threshold voltage increases
Solution Approach 1:
The patent applies local quality by creating a gradient boron composition within the free layer, where the boron concentration varies continuously from the interface with the pinned layer to the top surface. This gradient structure allows different regions of the same layer to have different chemical compositions and magnetic properties, optimizing both the layer structure and maintaining high internal stiffness throughout the free layer.
Solution Approach 2:
The patent changes the chemical composition parameter of the free layer by controlling boron concentration distribution. Instead of forming distinct separated layers, the invention maintains a continuous composition gradient with boron concentration decreasing from approximately 20-30% at the pinned layer interface to 0-10% at the top surface, which preserves magnetic stiffness while achieving structural optimization.
2Ease of manufacture
If the free layer is made with uniform boron content, then the deposition process is simple, but the internal stiffness is insufficient and switching current is high
Solution Approach 1:
The patent changes the boron concentration parameter from uniform to gradient distribution. The free layer is deposited with boron concentration varying from approximately 20-30% at the pinned layer interface to 0-10% at the top surface, creating a composition gradient that enhances internal stiffness while maintaining manufacturing feasibility through controlled deposition processes.
3Strength
If multiple deposition and annealing steps are performed to create gradient structure, then internal stiffness is enhanced, but the manufacturing process becomes complex
Solution Approach 1:
The patent applies preliminary action by establishing the gradient boron composition during the initial deposition process itself, rather than requiring subsequent annealing steps to create the gradient. The free layer is deposited with controlled boron concentration variation from the start, and a single annealing step is then used to stabilize the structure, significantly reducing process complexity compared to multiple deposition and annealing cycles.
4Ease of operation
If the threshold voltage is reduced for practical applications, then the device becomes usable, but the internal stiffness must be increased which requires complex layer structures
Solution Approach 1:
The patent changes the boron concentration parameter to create a gradient distribution that reduces threshold voltage for practical applicability. The free layer composition transitions from approximately 20-30% boron at the pinned layer interface to 0-10% at the top surface, achieving lower switching currents without requiring complex multi-layer structures.
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 enhanced internal stiffness reduces the switching voltage and current requirements, improving the efficiency and coherence of magnetization switching in STTMRAM elements, leading to easier and more efficient data storage.
Implementation Method 1
annealing the STTMRAM element at a first temperature after depositing the first free sub-layer to reduce the B content at an interface between the first free sub-layer and the barrier layer
Implementation Method 2
depositing a first free sub-layer on top of a barrier layer... depositing a third free sub-layer directly on top of the second free sub-layer
Data Source
AI summary
A spin transfer torque magnetic random access memory (STTMRAM) element and a method of manufacturing the same is disclosed having a free sub-layer structure with enhanced internal stiffness. A first free sub-layer is deposited, the first free sub-layer being made partially of boron (B), annealing is performed of the STTMRAM element at a first temperature after depositing the first free sub-layer to reduce the B content at an interface between the first free sub-layer and the barrier layer, the annealing causing a second free sub-layer to be formed on top of the first free sub-layer and being made partially of B, the amount of B of the second free sub-layer being greater than the amount of B in the first free sub-layer. Cooling down the STTMRAM element to a second temperature that is lower than the first temperature and depositing a third free sub-layer directly on top of the second free layer, with the third free sub-layer being made partially of boron (B), wherein the amount of B in the third sub-free layer is less than the amount of B in the second free sub-layer.