Perpendicular Magnetoresistive Element for Low-Current MRAM
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Solution Overview
Problem
Miniaturization of magnetoresistive elements for high-capacity magnetic random access memory (MRAM) faces challenges due to increased coercive force and thermal disturbance issues, making it difficult to maintain magnetization direction and reduce writing current simultaneously.
Innovation Solution
A magnetoresistive element with a perpendicular magnetization configuration using a multilayered structure of ferromagnetic materials with varying magnetic anisotropy constants and film thicknesses, where the storage layer has a smaller perpendicular magnetic anisotropy and a thinner first ferromagnetic material, allowing for reduced saturated magnetization and magnetic relaxation, enabling low-current magnetization reversal while maintaining thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the element size is reduced to achieve high-capacity memory, then the storage capacity increases, but the coercive force increases and writing current increases
Solution Approach 1:
The patent changes the magnetization configuration from in-plane to perpendicular, fundamentally altering the magnetic anisotropy parameters. This enables the storage layer to maintain stable magnetization at smaller sizes with lower coercive force, resolving the contradiction between miniaturization and writing current requirements
Solution Approach 2:
The patent employs a composite multilayer structure including CoFeB storage layer, CoFeB pinned layer, Ru spacer layer, and MgO tunnel barrier. This composite structure provides both perpendicular magnetic anisotropy for thermal stability and spin-polarized current for efficient spin transfer torque writing, enabling simultaneous achievement of miniaturization and low writing current
2Quantity of substance
If the element size is reduced to achieve high-capacity memory, then the storage capacity increases, but thermal disturbance increases and magnetization direction stability decreases
Solution Approach 1:
The patent introduces perpendicular magnetic anisotropy by changing the magnetization configuration, which fundamentally alters the energy barrier characteristics. The perpendicular magnetization provides a higher energy barrier against thermal disturbance compared to in-plane magnetization, enabling stable data retention even as element size decreases for high capacity
Solution Approach 2:
The patent applies different material compositions and thicknesses to different layers: the CoFeB storage layer with specific thickness provides perpendicular anisotropy and thermal stability, while the Ru spacer layer provides exchange coupling, and the MgO layer provides tunnel barrier function. This local optimization of each layer's properties achieves overall thermal stability in miniaturized elements
3Reliability
If countermeasures such as increasing aspect ratio or film thickness are taken to increase magnetic anisotropic energy, then thermal stability improves, but inversion current increases
Solution Approach 1:
The patent inverts the conventional approach by using perpendicular magnetization instead of in-plane magnetization. This inversion fundamentally changes the relationship between magnetic anisotropy and inversion current, enabling thermal stability to be achieved through perpendicular anisotropy while maintaining low inversion current via spin transfer torque mechanism
Solution Approach 2:
The patent replaces the conventional magnetic field-based writing mechanism with spin transfer torque writing. By injecting spin-polarized current through the tunnel junction, the magnetization is reversed through spin angular momentum transfer rather than external magnetic field, significantly reducing the current required for inversion while maintaining thermal stability
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 configuration enables both miniaturization and low-current magnetization reversal with improved thermal stability, addressing the limitations of in-plane magnetization configurations and achieving high thermal disturbance resistance.
Implementation Method 1
a write (spin injection write) system using spin momentum transfer (SMT) is suggested. According to this system, a spin polarized current is flowed through a magnetoresistive element to reverse a magnetization direction of a storage layer
Implementation Method 2
When a current is flowed through this ferromagnetic tunnel junction, the current tunnels through the insulator layer to flow. At this time, the resistance in the junction unit changes depending on a relative angle of the magnetization directions of the storage layer and the fixed layer
Data Source
AI summary
According to one embodiment, a magnetoresistive element includes a first magnetic layer with a perpendicular and variable magnetization, a second magnetic layer with a perpendicular and invariable magnetization, and a first nonmagnetic layer between the first and second magnetic layer. The first magnetic layer has a laminated structure of first and second ferromagnetic materials. A magnetization direction of the first magnetic layer is changed by a current which pass through the first magnetic layer, the first nonmagnetic layer and the second magnetic layer. A perpendicular magnetic anisotropy of the second ferromagnetic material is smaller than that of the first ferromagnetic material. A film thickness of the first ferromagnetic material is thinner than that of the second ferromagnetic material.