STT-MRAM Storage Element With Tilted Fixed Layer for Fast Writing
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Solution Overview
Problem
STT-MRAMs face challenges in achieving low power consumption and large capacity due to variations in spin torque that affect magnetization reversal times, leading to potential write errors and prolonged writing operations.
Innovation Solution
A storage element with a layer structure including a storage layer and a magnetization fixed layer, where the magnetization fixed layer is composed of two ferromagnetic layers with a coupling layer in between, tilted from a perpendicular direction, allowing for efficient magnetization reversal by current flow in the lamination direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a current magnetic field produced by a wiring is used for magnetization reversal in MRAM, then high-speed rewriting and high reliability are achieved, but power consumption increases and capacity expansion is limited
Solution Approach 1:
The patent replaces the conventional current magnetic field method (electromagnetic induction) with spin-torque magnetization reversal, which utilizes the spin angular momentum of electrons directly to reverse magnetization. This substitution eliminates the need for high current loops and achieves lower power consumption while maintaining high-speed rewriting capability
Solution Approach 2:
The patent changes the fundamental parameter of magnetization reversal from field-induced (external magnetic field) to torque-induced (spin transfer torque). By changing the reversal mechanism parameter, the system achieves both low power consumption and high-speed operation simultaneously, resolving the contradiction between power efficiency and speed
2Use of energy by moving object
If spin-torque magnetization reversal is used, then power consumption is reduced and scaling is possible, but variations in spin torque cause magnetization reversal time to vary, leading to write errors
Solution Approach 1:
The patent introduces local quality by creating an intermediate layer with specific magnetic properties between the storage layer and magnetization fixed layer. This intermediate layer has tailored exchange coupling characteristics that locally modify the magnetic environment, ensuring uniform spin torque distribution and consistent magnetization reversal time across different regions
Solution Approach 2:
The patent changes the magnetic coupling parameter between layers by introducing the intermediate layer with controlled exchange interaction. This parameter adjustment ensures that spin torque is uniformly transmitted, reducing variations in reversal time and improving write accuracy while maintaining low power consumption
3Loss of time
If the direction of magnetization of ferromagnetic layers is tilted from perpendicular direction, then magnetization reversal time is shortened and write errors are reduced, but device structure becomes more complex
Solution Approach 1:
The patent applies asymmetry by tilting the magnetization direction of ferromagnetic layers from the perpendicular (symmetric) direction to an oblique angle. This asymmetric orientation optimizes the spin torque efficiency and reduces magnetization reversal time, accepting the trade-off of increased structural complexity in the magnetization fixed layer
Solution Approach 2:
The patent segments the magnetization fixed layer into multiple ferromagnetic layers with an intermediate coupling layer, allowing independent optimization of each layer's magnetization direction. This segmentation enables the tilted orientation configuration that reduces reversal time while managing the complexity through modular layer design
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 reliable and high-speed writing operations by reducing write errors and shortening the time required for magnetization reversal, enhancing the storage apparatus's performance in terms of reliability and speed.
Implementation Method 1
when spin-polarized electrons passing through a magnetic layer fixed to a certain orientation enter another magnetic free layer (without fixed orientation), the spin-polarized electron exert spin torque on the magnetic free layer
Implementation Method 2
the magnetization fixed layer has two ferromagnetic layers laminated interposing a coupling layer therebetween, the ferromagnetic layers being magnetically coupled interposing the coupling layer
Data Source
AI summary
A storage element includes a layer structure including a storage layer having a direction of magnetization which changes according to information, a magnetization fixed layer having a fixed direction of magnetization, and an intermediate layer disposed therebetween, which intermediate layer contains a nonmagnetic material. The magnetization fixed layer has at least two ferromagnetic layers having a direction of magnetization tilted from a direction perpendicular to a film surface, which are laminated and magnetically coupled interposing a coupling layer therebetween. This configuration may effectively prevent divergence of magnetization reversal time due to directions of magnetization of the storage layer and the magnetization fixed layer being substantially parallel or antiparallel, reduce write errors, and enable writing operation in a short time.