Spin Accumulation Torque MRAM Cell Design
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Solution Overview
Problem
Existing MRAM memory cells face challenges in scaling due to bit disturbs, magnetic stability issues, and high current requirements, with previous techniques like field-induced switching and spin-transfer-torque switching having limitations such as adjacent bit disturbs and tunnel barrier degradation.
Innovation Solution
A new MRAM memory cell design utilizing spin accumulation torque, which includes a magnetic tunnel junction, a spin accumulation layer, and a ferromagnetic polarization layer, allowing for deterministic switching without external fields and minimizing write current through the tunnel barrier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If field-induced switching is used to write data to MRAM memory cells, then data can be written by generating magnetic fields, but adjacent bit disturbs occur affecting neighboring cells
Solution Approach 1:
The patent applies local quality by making the magnetization switching localized to the target memory cell through spin accumulation. The spin-polarized current is confined to flow through the selected MTJ, creating a localized spin accumulation effect that switches only the intended free layer magnetization without generating broad magnetic fields that would disturb adjacent bits.
Solution Approach 2:
The patent introduces a spin accumulation layer as an intermediary between the current path and the free layer. This intermediary layer accumulates spin-polarized electrons and transfers them to the free layer, enabling deterministic magnetization switching without requiring external magnetic fields that cause adjacent bit disturbs.
2Adaptability or versatility
If spin-transfer-torque switching is used to switch magnetization, then switching can be achieved without external fields, but high current degrades the tunnel barrier
Solution Approach 1:
The spin accumulation layer serves as an intermediary that reduces the direct impact of high current on the tunnel barrier. By accumulating spins in this intermediate layer before transferring to the free layer, the patent achieves magnetization switching with lower current density through the MTJ, preventing tunnel barrier degradation while maintaining field-free operation.
Solution Approach 2:
The patent segments the magnetization switching process into two stages: first, spin-polarized electrons are injected and accumulated in the spin accumulation layer; second, the accumulated spins transfer to the free layer to induce magnetization switching. This segmentation allows the current to be distributed over a longer duration at lower density, reducing stress on the tunnel barrier.
3Ease of manufacture
If conventional MRAM memory cell designs are used, then manufacturing can proceed with existing processes, but the cells are overly complicated to manufacture
Solution Approach 1:
The patent merges the spin injection layer and the free layer into a unified magnetic tunnel junction structure with a spin accumulation layer. This integration reduces the number of separate components and simplifies the manufacturing process while achieving deterministic magnetization switching, making the design more manufacturable compared to conventional complex MRAM cell 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
This design enhances switching efficiency and stability, reduces disturb problems, and allows for scalable MRAM cell sizes without high write current stress on the tunnel barrier.
Implementation Method 1
A spin accumulation layer (SAL) electrically connected to the magnetic tunnel junction and a first polarization layer electrically connected to the SAL. The SAL accumulates spins injected from the polarization layer, and the accumulated spins diffuse into the free layer to change its magnetization direction.
Implementation Method 2
applying a write current at the second terminal into the polarization layer; spin polarizing electrons of the write current as they pass through the polarization layer; injecting the spin polarized electrons into the spin accumulation layer
Implementation Method 3
diffusing at least some of the spin polarized electrons from the spin accumulation layer to a free layer of the magnetic tunnel junction; the spin polarized electrons imparting a torque on the free layer
Implementation Method 4
magnetoresistive random access memory (MRAM), which uses magnetization to represent stored data, in contrast to other memory technologies that use electronic charges to store data. A bit is read by measuring the resistance of the memory cell
Data Source
AI summary
An MRAM memory cell is proposed that is based on spin accumulation torque. One embodiment includes a magnetic tunnel junction, a spin accumulation layer connected to the magnetic tunnel junction and a polarization layer connected to the spin accumulation layer. The polarization layer and the spin accumulation layer use spin accumulation to provide a spin accumulation torque on the free magnetic layer of the magnetic tunnel junction to change direction of magnetization of the free magnetic layer.