Elliptical MTJ MRAM Cell with Perpendicular Anisotropy
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Solution Overview
Problem
Conventional Magnetic Random Access Memories (MRAMs) face challenges in achieving low power consumption and thermal stability while maintaining writing selectivity, due to variations in junction aspect ratio during fabrication, leading to increased power consumption and dispersion in writing fields.
Innovation Solution
The implementation of a thermally assisted switching (TAS) MRAM cell with an anisotropic magnetic tunnel junction shape, such as elliptical or rectangular, and a magnetocrystalline anisotropy axis perpendicular to the junction's long axis, reduces the dependence on aspect ratio variations for writing fields, thereby minimizing power consumption and ensuring thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MTJ-based MRAM uses high aspect ratio junctions (AR ≥ 1.5) to ensure thermal stability and writing selectivity, then thermal stability and writing selectivity are improved, but manufacturing precision deteriorates due to high sensitivity to aspect ratio variations
Solution Approach 1:
The patent changes the aspect ratio parameter from conventional high values (AR ≥ 1.5) to a new range (1.0 ≤ AR < 1.5), and introduces a specific magnetocrystalline anisotropy orientation (perpendicular to the long axis) to compensate for the reduced shape anisotropy, thereby maintaining thermal stability while improving manufacturing tolerance
Solution Approach 2:
The patent employs an anisotropic junction shape (elliptical or rectangular) with specific orientation of magnetocrystalline anisotropy perpendicular to the long axis, creating an asymmetric magnetic energy landscape that provides stable writing fields despite variations in aspect ratio
2Reliability
If conventional MTJ-based MRAM uses high aspect ratio junctions to achieve writing selectivity, then writing selectivity is improved, but power consumption increases due to higher writing fields required
Solution Approach 1:
The patent modifies the junction aspect ratio to a lower range (1.0 ≤ AR < 1.5) and orientes the magnetocrystalline anisotropy perpendicular to the long axis, which reduces the writing field requirement and consequently lowers power consumption while preserving writing selectivity through the anisotropic shape design
3Manufacturing precision
If conventional MTJ-based MRAM uses circular junctions to reduce dependence on aspect ratio, then manufacturing precision is improved, but writing field control deteriorates due to loss of shape anisotropy
Solution Approach 1:
The patent deliberately employs anisotropic junction shapes (elliptical or rectangular) rather than circular shapes, and orients the magnetocrystalline anisotropy perpendicular to the long axis to create a controlled asymmetric magnetic energy landscape that provides stable writing fields while maintaining reasonable manufacturing tolerance
Solution Approach 2:
The patent combines the geometric anisotropy of the junction shape with the magnetocrystalline anisotropy of the ferromagnetic layer, creating a composite magnetic anisotropy system where both shape and material properties contribute to the overall magnetic stability and writing field control
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 results in reduced power consumption and improved thermal stability, with a decreased variation in writing fields, allowing for more efficient and scalable MRAM cell design.
Implementation Method 1
Magnetic random access memories (MRAMs) have been the object of a renewed interest with the discovery of magnetic tunnel junctions (MTJ) having a strong magnetoresistance at ambient temperature
Implementation Method 2
The implementation of a thermally assisted switching (TAS) MRAM cell with an anisotropic magnetic tunnel junction shape
Implementation Method 3
a magnetocrystalline anisotropy axis perpendicular to the junction's long axis
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The present invention concerns a magnetic tunnel junction (MTJ) -based magnetic random access memory (MRAM) cell (1) with a thermally assisted switching (TAS) writing procedure comprising a magnetic tunnel junction (2) formed from a ferromagnetic storage layer (21a) having a magnetization that is adjustable above a high temperature threshold, a reference layer (23) having a fixed magnetization, and an insulating layer (22) being disposed between the storage and reference layers (21 a, 23); characterized in that the junction (2) has an anisotropic shape, and wherein the ferromagnetic storage layer (21 a) has a magnetocrystalline anisotropy being oriented essentially perpendicular to the long axis of the anisotropic shape of the junction (2). The TAS MTJ-based MRAM cell of the present invention limits advantageously the effects of the junction shape anisotropy dispersion coming from the fabrication process and has a lower power consumption in comparison with conventional MTJ-based MRAM and TAS MTJ-based MRAM cells of the prior art.