Stepped Bottom SOT Electrode for MRAM Back-Sputtering Prevention
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Solution Overview
Problem
Spin-orbit-torque (SOT) MRAM devices face challenges in yield due to back-sputtering of heavy metal particles during magnetic tunnel junction (MTJ) ion beam etch and require a bottom heavy metal SOT plate with high spin-orbit torque efficiency to induce spin current effectively.
Innovation Solution
A method is developed to form a stepped-shaped bottom SOT electrode by creating a sacrificial layer above the SOT electrode, forming a SOT via within this layer, and constructing a magnetic tunnel junction pillar with sidewall spacers, which prevents back-sputtering and enhances spin-inducing capabilities by ensuring the SOT electrode matches the size of the MTJ pillar.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a standard planar SOT electrode is used, then the device structure is simple, but back-sputtering of heavy metal particles occurs during MTJ ion beam etch
Solution Approach 1:
The SOT electrode is segmented into two distinct levels: a first SOT electrode at a lower level and a second SOT electrode at a higher level. This segmentation creates a stepped configuration that prevents back-sputtering during MTJ etching while maintaining manufacturing feasibility through standard deposition and etching processes.
Solution Approach 2:
The invention transitions from a two-dimensional planar electrode to a three-dimensional stepped electrode structure. The second SOT electrode is positioned at a higher elevation than the first, creating vertical dimensionality that blocks the back-sputtering pathway during ion beam etching of the MTJ layer.
2Reliability
If the SOT electrode is made larger to improve spin-inducing capabilities, then spin current induction is enhanced, but the electrode becomes misaligned with the MTJ pillar
Solution Approach 1:
The stepped SOT electrode structure provides different functional zones: the wider first SOT electrode at the lower level provides enhanced spin current induction area, while the smaller second SOT electrode at the higher level provides precise alignment with the MTJ pillar. Each level has optimized dimensions for its specific function.
Solution Approach 2:
The second SOT electrode is nested above and aligned with the first SOT electrode, creating a hierarchical structure where the smaller upper electrode is positioned within the footprint of the larger lower electrode. This nesting arrangement ensures both alignment and enhanced spin-inducing capability.
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 prevents back-sputtering of heavy metals during etching, improves spin-inducing capabilities, and enhances the yield of SOT-MRAM devices by ensuring the SOT electrode effectively matches the size and structure of the MTJ pillar.
Implementation Method 1
spin-orbit-torque (SOT) magneto-resistive random access memory
Data Source
AI summary
A memory structure, and a method for forming the same, includes a spin-orbit-torque electrode within a dielectric layer located above a substrate. The spin-orbit-torque electrode including a first conductive material, and a spin-orbit torque via is directly above the spin-orbit-torque electrode that includes a second conductive material. A magnetic tunnel junction pillar is directly above the spin-orbit torque via, and the spin-orbit-torque via contacting a center of a bottom surface of the magnetic-tunnel-junction pillar. A third conductive material is positioned directly below the bottom surface of the magnetic tunnel junction pillar on opposite sides of the spin-orbit torque via and directly above the spin-orbit-torque electrode. The third conductive material, the spin-orbit torque electrode and the spin-orbit torque via form a bottom spin-orbit torque electrode of the magnetic tunnel junction pillar.