Self-Referenced MRAM Cell Dipolar Coupling Reduction
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Solution Overview
Problem
Self-referenced MRAM cells face increased power consumption due to dipolar coupling between storage and sense layers, especially when scaling down, which affects switching field and read operation efficiency.
Innovation Solution
The method involves a magnetic tunnel junction with a synthetic storage layer and a sense layer, where the dipolar coupling is minimized by selecting appropriate thicknesses and materials for the ferromagnetic layers, and using spin-transfer torque write operations with spin-polarized currents to switch the magnetization without applying a magnetic field, allowing for low power consumption writing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the magnetic tunnel junction diameter is decreased to scale down the MRAM cell, then the device size is reduced, but the dipolar coupling between storage and sense layers increases
Solution Approach 1:
The patent changes the magnetic parameters of the storage layer by using a synthetic storage layer with antiparallel coupled ferromagnetic layers. By adjusting the magnetization directions and magnitudes of the individual layers, the net stray field is reduced, thereby decreasing the dipolar coupling effect while maintaining the scaled-down device dimensions
Solution Approach 2:
The patent employs a composite storage layer structure consisting of multiple ferromagnetic layers with different magnetization orientations coupled through a non-magnetic layer. This composite structure allows the storage layer to generate reduced stray fields compared to a single-layer structure, effectively lowering dipolar coupling in miniaturized cells
2Object-generated harmful factors
If the stray field is decreased by using a synthetic storage layer, then the dipolar coupling is reduced, but the switching field of the sense layer magnetization increases
Solution Approach 1:
The patent extracts the harmful stray field component by separating the storage layer into multiple ferromagnetic layers with antiparallel magnetization. The opposing magnetizations cancel each other's stray field contribution, removing the harmful dipolar coupling effect while preserving the necessary magnetic storage functionality
Solution Approach 2:
The patent modifies the magnetic field application strategy by using spin-polarized current to switch the storage layer magnetization instead of relying solely on external magnetic fields. This changes the switching mechanism parameters, allowing the sense layer to be switched with lower external fields despite the reduced stray field assistance
3Ease of operation
If a magnetic field is applied to switch the sense layer magnetization, then the switching operation is achieved, but the power consumption increases
Solution Approach 1:
The patent replaces the magnetic field-based switching mechanism with a spin-transfer torque mechanism. Instead of using external magnetic fields to switch magnetization, spin-polarized current flowing through the magnetic tunnel junction exerts torque on the magnetic moments, achieving switching with lower power consumption
Solution Approach 2:
The patent utilizes the phase transition-like switching of magnetization direction through spin-transfer torque. The spin-polarized current induces a sudden reorientation of magnetic moments from one stable state to another, analogous to a phase transition, enabling efficient switching without continuous energy input from external magnetic fields
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 approach enables efficient writing to MRAM cells with reduced power consumption by nullifying dipolar coupling and stabilizing sense magnetization, thereby improving switching efficiency and reducing stray field effects.
Implementation Method 1
switching the second ferromagnetic magnetization by passing a spin-polarized current in the magnetic tunnel junction
Implementation Method 2
a dipolar coupling between the storage and sense layers occurs due to local magnetic stray field, coupling the magnetization of the sense layer with the one of the storage layer
Data Source
AI summary
The present disclosure concerns a method for writing to a self-referenced MRAM cell comprising a magnetic tunnel junction comprising: a storage layer including a first ferromagnetic layer having a first storage magnetization, a second ferromagnetic layer having a second storage magnetization, and a non-magnetic coupling layer separating the first and second ferromagnetic layers; a sense layer having a free sense magnetization; and a tunnel barrier layer included between the sense and storage layers; the first and second ferromagnetic layers being arranged such that a dipolar coupling between the storage) and the sense layers is substantially null; the method comprising: switching the second ferromagnetic magnetization by passing a spin-polarized current in the magnetic tunnel junction; wherein the spin-polarized current is polarized when passing in the sense layer, in accordance with the direction of the sense magnetization. The MRAM cell can be written with low power consumption.