Tilted Fixed-Layer MRAM Structure for Faster Accurate 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 has two ferromagnetic layers tilted from a perpendicular direction, and an intermediate nonmagnetic layer, allowing for efficient magnetization reversal through current flow in the lamination direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If spin-torque magnetization reversal is used for high-speed rewriting, then rewriting speed is improved, but variations in magnetization reversal time cause write errors and reliability deteriorates
Solution Approach 1:
The patent changes the magnetization direction parameter from perpendicular to inclined (e.g., 45 degrees) relative to the film surface. This parameter change ensures that the spin torque never becomes zero during the reversal process, as the magnetization direction never aligns perfectly with or against the spin polarization direction. This maintains consistent reversal dynamics and prevents timing variations that cause write errors.
Solution Approach 2:
The patent preliminarily sets the magnetization direction of the fixed layer to an inclined angle before the write operation begins. This preliminary configuration ensures that during subsequent write operations, the spin torque will always have a non-zero component acting on the storage layer, pre-establishing conditions for reliable and consistent magnetization reversal timing.
2Productivity
If magnetization reversal time is reduced for faster writing, then productivity is improved, but write errors increase due to insufficient reversal completion
Solution Approach 1:
By changing the magnetization direction from perpendicular to inclined, the patent ensures that the spin torque maintains a consistent non-zero magnitude throughout the reversal process. This parameter change creates a more uniform and predictable reversal trajectory, allowing for optimized write pulse durations that complete reversal reliably without requiring excessive time margins.
3Device complexity
If perpendicular magnetization direction is used for simple structure, then device complexity is reduced, but spin torque becomes zero at certain angles causing magnetization reversal time to extend
Solution Approach 1:
The patent introduces asymmetry by tilting the magnetization direction from the perpendicular axis to an inclined angle (e.g., 45 degrees). This asymmetric configuration breaks the symmetry that causes spin torque to become zero at parallel and antiparallel alignment points in perpendicular magnetization systems. The asymmetric geometry ensures continuous non-zero spin torque action throughout the reversal process.
Solution Approach 2:
The magnetization direction is preliminarily configured at an inclined angle during fabrication, establishing a geometric condition that prevents spin torque from reaching zero during operation. This preliminary geometric setup eliminates the need for complex control mechanisms to manage reversal timing variations.
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 reduces write errors and enables faster writing operations, enhancing the reliability and speed of the storage apparatus by ensuring magnetization reversal within a predetermined time.
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. When a current above a certain threshold flows, a free magnetization layer (storage layer) would reverse its direction of magnetization.
Implementation Method 2
a method of reversing magnetization by a current magnetic field produced by a wiring... spin-torque magnetization reversal... allows a current to flow in the layer structure in its lamination direction to cause change in the direction of magnetization of the storage 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.