MTJ Element Stray Field Reduction via Optimized SAF Structure
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Solution Overview
Problem
Magnetoresistive random access memory (MRAM) devices face challenges in write efficiency and data retention due to strong lateral-direction stray magnetic fields caused by the magnetization of reference layers, which deteriorate the element characteristics and make it difficult to achieve improved write efficiency.
Innovation Solution
The implementation of a dual junction magnetic tunnel junction (MTJ) element with a synthetic anti-ferromagnetic (SAF) structure and a sidewall spacer, where the thickness and magnetic field of each layer are optimized to reduce the stray magnetic field, thereby improving write efficiency and data retention characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reference layer with fixed magnetization is used in MTJ element, then data retention is improved, but lateral-direction stray magnetic field increases causing deterioration of element characteristics
Solution Approach 1:
A nonmagnetic layer is introduced between the reference layer and the storage layer to act as an intermediary that blocks or reduces the stray magnetic field generated by the reference layer's fixed magnetization, thereby preventing deterioration of element characteristics while maintaining data retention capability
Solution Approach 2:
The stray magnetic field generated by the reference layer is converted into a beneficial effect by designing the magnetization direction and thickness of the reference layer such that the stray field assists in stabilizing the magnetization state of the storage layer, improving data retention without causing harmful effects
2Reliability
If reference layer thickness is increased to improve data retention, then magnetization stability is improved, but stray magnetic field strength increases making write operation difficult
Solution Approach 1:
The thickness of the reference layer is optimized to a specific range (5-15 nm) and the magnetization direction is set to perpendicular orientation, changing these parameters to achieve a balance where sufficient magnetization stability is obtained while stray magnetic field strength is reduced to enable successful write operations
Solution Approach 2:
Different regions of the magnetic layer structure are assigned different properties: the reference layer has perpendicular magnetization with optimized thickness for stability, while the storage layer has in-plane magnetization optimized for writeability, creating local quality differences that resolve the contradiction
3Device complexity
If conventional single junction MTJ structure is used, then device complexity is low, but write efficiency is insufficient due to strong stray magnetic field influence
Solution Approach 1:
The magnetic layer is segmented into distinct functional regions: a reference layer with perpendicular magnetization for stability and a storage layer with in-plane magnetization for writeability, separated by a nonmagnetic layer. This segmentation allows each region to be optimized independently, improving write efficiency while maintaining manageable device complexity
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
The optimized SAF structure and sidewall spacer configuration minimize the influence of stray magnetic fields, enhancing write efficiency and data retention in the MTJ element by allowing for easier magnetization direction reversal and reducing lateral-direction stray magnetic field effects.
Implementation Method 1
one of the two magnetic layers being a magnetization fixed layer (reference layer) in which the magnetization is fixed so that the direction of magnetization does not change, the other being a magnetization free layer (storage layer) which the direction of magnetization may be easily reversed
Implementation Method 2
a large-capacity magnetoresistive random access memory (MRAM) using a magnetic tunnel junction (MTJ) element has been expected and attracting attention
Data Source
AI summary
According to one embodiment, a magnetoresistive memory device includes a first magnetic layer, a second magnetic layer on one major surface side of the first magnetic layer via a first nonmagnetic layer, a third magnetic layer on the second magnetic layer via a first Ru layer, a sidewall insulating film on sides of the layers, a fourth magnetic layer on an other major surface side of the first magnetic layer via a second nonmagnetic layer, and a fifth magnetic layer on the fourth magnetic layer via a second Ru layer. The reversed magnetic field of the second magnetic layer is smaller than that of the third and fourth magnetic layers, and the reversed magnetic field of the fifth magnetic layer is smaller than that of the third and fourth magnetic layers.