Magnetoresistive Element with Opposing Fixed Layers for MRAM Write Stability
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Solution Overview
Problem
Magnetic memory (MRAM) using tunneling magnetoresistive effect elements faces issues with low signal ratio between write and read currents, leading to write errors due to variations in read and write currents, which necessitates controlling the magnetization direction variations in the fixed layer.
Innovation Solution
A magnetoresistive effect element structure is designed with multiple ferromagnetic and nonmagnetic layers, including a free layer with variable magnetization direction and fixed layers with invariable magnetization direction, along with spacer layers to adjust and stabilize the magnetization direction, allowing for both upward and downward spin transfer to reduce variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional tunneling magnetoresistive effect element structure is used, then the device complexity is low, but the reliability is poor due to write errors caused by current variations
Solution Approach 1:
The patent divides the magnetoresistive effect element into multiple functional layers: a first fixed layer, a free layer, and a second fixed layer, each with specific magnetization directions. This segmentation allows independent control of spin transfer directions, enabling reliable writing operations by canceling out current variations through opposite spin transfer effects on the first and second fixed layers.
Solution Approach 2:
The patent assigns different magnetization directions to different layers: the first fixed layer has in-plane magnetization, the free layer has perpendicular magnetization, and the second fixed layer has in-plane magnetization opposite to the first. This local quality differentiation enables selective spin transfer directions from the free layer to each fixed layer, resolving the reliability issue by making the system insensitive to current variations.
2Stability of the object's composition
If the magnetization direction in the fixed layer is made variable to increase operation margin, then the operation margin increases, but the manufacturing precision requirement increases due to need for precise magnetization control
Solution Approach 1:
The patent establishes the magnetization directions of the first and second fixed layers during the manufacturing process before device operation. The first fixed layer is given in-plane magnetization and the second fixed layer is given opposite in-plane magnetization. This preliminary action ensures that during operation, spin transfer from the free layer will naturally act in opposite directions on the two fixed layers, canceling out variations and maintaining stability without requiring additional precision control during operation.
3Reliability
If multiple fixed layers with opposite magnetization directions are introduced, then the reliability improves by canceling current variations, but the device complexity increases
Solution Approach 1:
The patent combines the functions of reading and writing operations into a single current path through the stack. The same current that passes through the free layer for reading also provides spin transfer for writing to the first and second fixed layers. This merging eliminates the need for separate write and read current paths, reducing overall system complexity despite adding layers, while improving reliability through the opposite spin transfer mechanism.
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 structure reduces variations in read and write currents, enhancing the operation margin and preventing data disturb errors by directly adjusting the magnetization direction in the fixed layer, thereby improving the reliability of MRAM operations.
Implementation Method 1
spins in one ferromagnetic material layer are fixed (or made invariable) (a fixed layer or pinned layer), and those in the other ferromagnetic material layer are controlled (or made variable) (a free layer or recording layer)
Implementation Method 2
An application to a magnetic memory (MRAM: Magnetoresistive Random Access Memory) using a tunneling magnetoresistance (TMR) effect element (or a magnetic tunnel junction (MTJ) element)
Data Source
AI summary
A magnetoresistive element includes first, second, and third fixed layers, first, second, and third spacer layers, and a free layer. The first fixed layer is made of a ferromagnetic material and having an invariable magnetization direction. The first spacer layer is formed on the first fixed layer and made of an insulator. The free layer is formed on the first spacer layer, made of a ferromagnetic material, and having a variable magnetization direction. The second spacer layer is formed on the free layer and made of a nonmagnetic material. The second fixed layer is formed on the second spacer layer, made of a ferromagnetic material, and having an invariable magnetization direction. The third spacer layer is formed below the first fixed layer and made of a nonmagnetic material. The third fixed layer is formed below the third spacer layer, made of a ferromagnetic material, and having an invariable magnetization direction.