SAF Magnetic Tunnel Junction Structure for Lower Field Interference
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Solution Overview
Problem
Existing magnetic devices face challenges in minimizing the negative effects of magnetic fields applied from fixed layers, which can impact the reliability and performance of magnetic random access memory (MRAM) devices.
Innovation Solution
The magnetic device incorporates a synthetic antiferromagnetic (SAF) structure with a simplified configuration, including a first fixed pattern, an antiferromagnetic coupling pattern, and a second fixed pattern, along with a nonmagnetic pattern and a polarization reinforcement magnetic pattern, to reduce the impact of magnetic fields and enhance reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional fixed layer structure is used in MTJ cell, then the device can be manufactured with standard processes, but the magnetic field applied from the fixed layer to the surroundings causes negative effects on reliability
Solution Approach 1:
The patent applies the 'Blessing in disguise' principle by converting the harmful magnetic field effect into a beneficial one. The synthetic antiferromagnetic (SAF) structure with alternating ferromagnetic layers (CoFeB, CoFe) and nonmagnetic spacer layers (Ru, Ta) creates antiparallel magnetization between adjacent ferromagnetic layers. This antiparallel configuration causes the magnetic fields from opposite sides to cancel each other out, transforming the originally harmful magnetic field interference into a beneficial field cancellation effect that improves device reliability.
Solution Approach 2:
The patent employs the 'Composite materials' principle by creating a composite SAF structure that combines multiple materials with different magnetic properties. The structure integrates ferromagnetic materials (CoFeB, CoFe) with nonmagnetic spacer materials (Ru, Ta) to form a composite system. This composite structure enables both the generation of perpendicular magnetic anisotropy (PMA) and the cancellation of magnetic fields, simultaneously achieving improved reliability and reduced magnetic field interference.
2Reliability
If multiple SAF structures are stacked to reinforce polarization, then the magnetic field cancellation effect is improved, but the surface roughness increases
Solution Approach 1:
The patent applies the 'Local quality' principle by optimizing the magnetization direction and magnetic properties at different locations within the SAF structure. The first ferromagnetic layer (CoFeB) is configured with perpendicular magnetization for strong PMA, while the second ferromagnetic layer (CoFe) is configured with in-plane magnetization. This local differentiation of magnetic properties enables effective field cancellation while maintaining smooth interfaces and reducing surface roughness, thereby improving both data retention and manufacturing precision.
3Device complexity
If the fixed layer structure is simplified to reduce complexity, then the manufacturing process is easier, but the ability to counteract magnetic field effects is reduced
Solution Approach 1:
The patent applies the 'Merging (Combining)' principle by integrating multiple functions into a single SAF structure. Instead of using separate structures for polarization reinforcement and field cancellation, the patent combines both functions into one SAF unit with alternating ferromagnetic and nonmagnetic layers. This merged structure simultaneously provides perpendicular magnetic anisotropy for polarization and antiparallel magnetization for field cancellation, reducing overall device complexity while maintaining effectiveness against magnetic field effects.
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 improves the data retention characteristic and reduces surface roughness, leading to enhanced reliability and performance of the magnetic device, particularly in high-integration and low-power consumption applications.
Implementation Method 1
an antiferromagnetic coupling pattern in contact with an upper surface of the first fixed pattern
Implementation Method 2
a magnetic device including a magnetic layer having perpendicular magnetic anisotropy (PMA)
Implementation Method 3
Research for electronic elements using a magnetoresistive characteristic of a magnetic tunnel junction (MTJ) has been conducted
Data Source
AI summary
A magnetic device includes a seed pattern, a reference magnetic structure on the seed pattern, a free magnetic pattern on the reference magnetic structure, and a tunnel barrier between the reference magnetic structure and the free magnetic pattern. The reference magnetic structure includes a synthetic antiferromagnetic (SAF) structure including a first fixed pattern in contact with an upper surface of the seed pattern, an antiferromagnetic coupling pattern in contact with an upper surface of the first fixed pattern, and a second fixed pattern in contact with an upper surface of the antiferromagnetic coupling pattern; a nonmagnetic pattern in contact with an upper surface of the second fixed pattern; and a polarization reinforcement magnetic pattern in contact with an upper surface of the nonmagnetic pattern.