MTJ Switching with Parallel Spin-Momentum Layer for Lower Current
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Solution Overview
Problem
Current STT-MRAM technologies face challenges in achieving lower switching currents and additional sources of spin-transfer-torque without complicating the fabrication process, particularly with dual MTJ structures and spin-orbit coupling torque methods.
Innovation Solution
Incorporating a parallel spin-momentum (PSM) layer with a chiral material adjacent to the free layer of the magnetic tunnel junction (MTJ) to provide an additional source of spin-transfer-torque, which is compatible with perpendicular magnetic anisotropy and reduces fabrication complexities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a dual MTJ structure is used to provide additional spin-transfer-torque, then switching current is reduced, but device complexity and fabrication difficulty increase due to thicker MTJ stacks
Solution Approach 1:
The patent transitions from a vertical dual-MTJ stack architecture to a lateral PSM layer configuration adjacent to the free layer. This dimensional change allows the spin torque source to be positioned horizontally rather than vertically stacked, reducing stack thickness while maintaining the additional spin transfer torque mechanism.
Solution Approach 2:
The patent introduces a parallel spin-momentum (PSM) layer as an intermediary component that generates spin current through spin-orbit coupling. This PSM layer acts as a mediator between the electrical current and the free layer magnetization, providing the additional spin torque without requiring a thicker MTJ stack.
2Use of energy by moving object
If SOT material is added adjacent to the free layer to provide spin-orbit coupling torque, then switching current is reduced, but fabrication complexity increases due to additional lateral SOT lines
Solution Approach 1:
The patent merges the PSM layer with the existing MTJ stack structure, forming an integrated unit where the PSM layer is deposited adjacent to the free layer within the same fabrication sequence. This integration eliminates the need for separate lateral SOT lines and reduces the number of fabrication steps.
Solution Approach 2:
The patent repositions the spin torque generation from a lateral configuration (requiring external SOT lines) to a vertical integration where the PSM layer is positioned adjacent to the free layer in the vertical stack, allowing current to flow through the PSM layer without requiring lateral extensions.
3Speed
If perpendicular magnetic anisotropy is used in the free layer, then switching speed is improved, but switching current increases compared to in-plane magnetization
Solution Approach 1:
The patent employs a composite structure combining the free layer with a PSM layer having specific spin-orbit coupling properties. This composite configuration leverages the spin Hall effect or Rashba effect in the PSM layer to generate additional spin torque that assists in switching the perpendicular magnetization, thereby reducing the required switching current while maintaining fast switching speeds.
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 PSM layer with chiral material allows for lower switching currents and improved stability, enhancing the scalability and power efficiency of STT-MRAM devices while simplifying the fabrication process by providing non-reciprocal spin currents that amplify the total torque, thus reducing the switching current requirements.
Implementation Method 1
a parallel spin-momentum (PSM) layer with a chiral material adjacent to the free layer of the magnetic tunnel junction (MTJ) to provide an additional source of spin-transfer-torque
Implementation Method 2
STT-MRAM changes the magnetic direction of the free layer by directly passing a spin-polarized current through the MTJ
Implementation Method 3
MTJs with positive tunnel magnetoresistance (TMR), when a sufficient current is driven in one direction perpendicular-to-plane
Implementation Method 4
smaller switching currents are needed if the magnetic layers have magnetization perpendicular to a film surface, i.e., have perpendicular magnetic anisotropy (PMA)
Data Source
AI summary
Methods and apparatuses are provided for MRAM devices utilizing spin transfer torque. A device includes a substrate; an MTJ formed over the substrate, the MTJ including a reference layer, a tunnel barrier layer, and a free layer; and a PSM layer formed over the free layer of the MTJ. The PSM layer, i.e., a chiral material layer, may be formed adject to a free layer (or adjacent to a TBL, which is adjacent to the free layer) of the MTJ, providing an additional source of spin-transfer-torque, and providing MTJ devices that are operable with lower switching current.