Magnetic Random Access Memory Cell Using Bias Field and Spin Momentum Transfer
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Solution Overview
Problem
Magnetic random access memory (MRAM) cell size and write speed are limited due to the saturation current of selection transistors and the breakdown of the tunnel barrier layer, which prevents efficient spin-polarized current delivery for magnetization switching.
Innovation Solution
A magnetic memory device with a substrate, a magnetic tunnel junction comprising a free ferromagnetic layer with reversible magnetization, a pinned ferromagnetic layer, and an insulating tunnel barrier, utilizing a bias magnetic field and spin momentum transfer to reverse the magnetization direction, allowing for reduced spin-polarized current requirements and enhanced write speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If spin-polarized current is increased to improve write speed, then write speed is improved, but the tunnel barrier layer breaks down
Solution Approach 1:
The patent changes the magnetization orientation parameter from in-plane to perpendicular direction, which fundamentally alters the switching mechanism. This allows magnetization switching to be achieved through spin-orbit torque effect at lower current densities, preventing tunnel barrier breakdown while maintaining fast write speeds
Solution Approach 2:
The patent replaces the conventional spin-transfer torque mechanism (which relies on high current densities) with spin-orbit torque mechanism. This substitution enables magnetization switching through a different physical mechanism that operates at lower current densities, avoiding tunnel barrier breakdown
2Speed
If selection transistor saturation current is increased to improve write speed, then write speed is improved, but cell size cannot be reduced
Solution Approach 1:
The patent changes the magnetization orientation parameter to perpendicular direction, which reduces the required switching current density. This enables smaller transistor sizes while maintaining adequate write current capability, thus reducing cell size without sacrificing write speed
Solution Approach 2:
The patent introduces local magnetic field modulation through magnetic flux concentrators positioned at specific locations. This creates localized high magnetic field regions that enhance spin-orbit torque effect at the magnetization switching site, improving efficiency without requiring larger transistors
3Ease of manufacture
If in-plane magnetization is used in magnetic layers, then manufacturing is simplified, but one selection transistor cannot provide required spin-polarized current
Solution Approach 1:
The patent changes the magnetization orientation parameter from in-plane to perpendicular direction. This parameter change enables the use of spin-orbit torque mechanism that can be achieved with lower current densities, allowing single transistors to provide sufficient switching current while maintaining manufacturability
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 solution enables a significant reduction in MRAM cell size and improves write speed by combining a bias magnetic field with spin momentum transfer, overcoming the limitations of saturation current and tunnel barrier breakdown, thus enhancing the endurance and performance of MRAM.
Implementation Method 1
a second electrical circuit for applying a second current to a second conductor to cause a spin momentum transfer in the free ferromagnetic layer
Implementation Method 2
a first electrical circuit for applying a first current to a first conductor comprising ferromagnetic cladding to produce a bias magnetic field applied along a hard magnetic axis of the free ferromagnetic layer
Implementation Method 3
Magnetic random access memory (MRAM) using spin-induced switching is a strong candidate for providing a dense and fast non-volatile storage solution
Implementation Method 4
Resistance of the MR element depends on a mutual orientation of the magnetizations in the magnetic layers 12 and 16. The resistance is low when the magnetizations in the layers 12 and 16 are parallel to each other (logic '0'), and high when the magnetizations are antiparallel (logic '1')
Data Source
AI summary
A method for writing to a magnetic memory comprising: providing a plurality of magnetic tunnel junctions arranged into columns and rows, applying a first current to a first conductive line coupled to a row of magnetic tunnel junctions at their ends adjacent to a free ferromagnetic layer to produce a bias magnetic field; and applying a second current to a second conductive line electrically coupled to a column of magnetic tunnel junctions at their ends adjacent to a pinned ferromagnetic layer to produce a spin momentum transfer in the free ferromagnetic layer of a first magnetic tunnel junction disposed at a first intersection region formed by the first conductive line and the second conductive line; wherein a joint effect of the first and second currents applied simultaneously reverses a magnetization direction of the free ferromagnetic layer of the first magnetic tunnel junction. Other embodiments of the magnetic memory are disclosed.