Stepped SOT-MRAM Stack to Prevent Bridge Shorts
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Solution Overview
Problem
Conventional spin-orbit-torque (SOT) magnetic random access memory (MRAM) fabrication methods often result in metal bridges forming across the barrier layer during etching, leading to electrical shorts and rendering the MRAM inoperable, and additional etching attempts to eliminate these bridges can cause excessive thinning of the SOT layer, increasing electrical resistance.
Innovation Solution
A method involving a dielectric pillar and a stepped SOT layer profile is used, where the SOT layer has an upper step directly under the magnetic tunnel junction (MTJ) stack and lower steps adjacent to it, allowing for additional etching without excessive thinning, and the use of a dielectric pillar and bars to prevent bridge formation by planarizing and depositing conductive materials in a specific sequence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SOT MRAM fabrication methods are used, then the manufacturing process is simple, but metal bridges form across the barrier layer causing electrical shorts
Solution Approach 1:
The SOT layer is divided into two distinct layers: a first SOT layer deposited over the entire substrate, and a second SOT layer deposited only in regions where the MTJ stack is absent. This segmentation prevents metal bridges from forming across the barrier layer while maintaining the spin-orbit torque functionality, thereby improving electrical integrity without significantly complicating the fabrication process
Solution Approach 2:
The first SOT layer is deposited in advance over the entire substrate before the MTJ stack fabrication. This preliminary action creates a protective base layer that prevents metal bridge formation during subsequent processing steps, eliminating the need for complex bridge removal or prevention techniques while ensuring electrical integrity
2Speed
If the SOT layer is made thinner to improve switching time, then switching speed increases, but the layer becomes too thin and unreliable
Solution Approach 1:
The SOT functionality is distributed across two separate layers: the first SOT layer provides structural stability and prevents bridging, while the second SOT layer enables fast switching. This segmentation allows each layer to be optimized independently - the first layer can be thicker for reliability, while the second layer can be thinner for speed
Solution Approach 2:
The dual SOT layer structure creates a composite system where the first SOT layer (deposited over the entire substrate) and second SOT layer (deposited in selective regions) work together. The composite structure combines the advantages of both layers: the first layer provides mechanical and electrical stability, while the second layer provides efficient spin-orbit torque for fast switching
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 approach enhances the reliability and switching time of SOT MRAM by eliminating metal bridges and maintaining low electrical resistance, thereby improving device endurance and read/write stability.
Implementation Method 1
The MRAM 100 SOT induces switching of the free layer 116 (for writing) by injecting an in-plane current from the first bottom electrode to the write electrode in the SOT layer 110
Implementation Method 2
spin-orbit-torque (SOT) magnetic random access memory (MRAM)
Data Source
AI summary
A magnetic random access memory (MRAM) apparatus includes a magnetic tunnel junction (MTJ) stack; a spin-orbit-torque (SOT) layer that underlies the MTJ stack; and a dielectric pillar that underlies the SOT layer and the MTJ stack. The SOT layer has a stepped profile.