STTMRAM Free Layer Boron Gradient for Magnetic Stiffness
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Solution Overview
Problem
Magnetic random access memory (MRAM) with magnetic tunnel junctions (MTJs) faces a challenge due to low internal magnetic stiffness, resulting in high threshold voltage/current requirements for switching the free layer magnetization, which hinders practical applications.
Innovation Solution
A spin transfer torque magnetic random access memory (STTMRAM) element with a free layer structure is developed, comprising sub-layers formed through a specific annealing process, where a first free sub-layer is deposited, annealed to reduce boron content at the interface, and then cooled to form a second sub-layer with higher boron content, followed by deposition of a third sub-layer with lower or no boron content, enhancing internal stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional free layer structure with uniform boron content is used, then the manufacturing process is simple, but the internal magnetic stiffness is low resulting in high threshold voltage requirements
Solution Approach 1:
The free layer is divided into multiple sub-layers with different boron concentrations. The first sub-layer has lower boron content (0-5 at%) and the second sub-layer has higher boron content (5-20 at%), creating a gradient structure that enhances overall magnetic stiffness while maintaining manufacturing feasibility through sequential deposition
Solution Approach 2:
Different regions of the free layer are given different boron concentrations to optimize local magnetic properties. The interface region with the barrier layer has lower boron for better coupling, while the upper region has higher boron for enhanced stiffness, creating locally optimized magnetic characteristics throughout the layer
2Strength
If the free layer is made with high boron content to enhance stiffness, then internal magnetic stiffness improves, but the threshold voltage for switching increases
Solution Approach 1:
The free layer employs a boron concentration gradient where the lower sub-layer near the barrier has 0-5 at% B for easy switching, while the upper sub-layer has 5-20 at% B for high stiffness. This local differentiation allows the system to achieve both low switching voltage and high stability simultaneously
Solution Approach 2:
The free layer is constructed as a composite structure with two distinct boron-containing sub-layers. This composite approach combines the advantages of low-boron regions (easy magnetization switching) with high-boron regions (high magnetic stiffness), achieving optimal overall performance
3Strength
If annealing is performed to reduce boron content at the interface, then magnetic stiffness is enhanced, but the manufacturing process complexity increases
Solution Approach 1:
The free layer is deposited with a predetermined boron concentration gradient before annealing, with the lower sub-layer already having lower boron content. This preliminary structuring reduces the extent of boron redistribution needed during annealing, simplifying the thermal processing requirements while achieving the desired interface composition
Solution Approach 2:
The manufacturing process utilizes controlled annealing at specific temperature ranges to induce selective boron diffusion. By adjusting annealing temperature and duration parameters, the process achieves optimal boron redistribution to enhance stiffness without requiring excessively complex multi-step thermal processing
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/current requirements, improving the efficiency and coherence of magnetization switching, leading to easier and more efficient data storage in MRAM.
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. The annealing causes a second free sub-layer to be formed on top of the first free sub-layer
Implementation Method 2
An exemplary MTJ uses spin torque transfer to effectuate a change in the direction of magnetization of one or more free layers in the MTJ. That is, writing bits of information is achieved by using a spin polarized current flowing through the MTJ
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.