Dual-Junction TMR MRAM for Multilevel Data Storage
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Solution Overview
Problem
Conventional magnetic random access memory (MRAM) technologies face limitations in miniaturization due to the need for large switching magnetic fields and currents, which restrict the reduction of cell size and, consequently, the scale of memory integration, especially when attempting to record multilevel data in a single cell.
Innovation Solution
A magnetic random access memory (MRAM) design utilizing a spin-transfer-magnetization-switching mechanism with a dual-junction TMR structure, featuring two tunnel barriers and two free layers with different switching current thresholds, allows for the recording and reading of at least three or four levels of data based on synthetic resistance, enabling increased integration per unit area without the need for complex write word lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional MRAM uses single-junction TMR structure with shape magnetic anisotropy, then device structure is simple, but switching magnetic field and current are large, preventing miniaturization
Solution Approach 1:
The patent divides the single TMR junction into two separate TMR junctions (first and second TMR junctions) with different magnetization orientations. The first TMR junction uses in-plane magnetization while the second uses perpendicular magnetization, allowing independent control of switching characteristics and enabling multilevel data storage in a segmented manner
Solution Approach 2:
The patent introduces a new dimension by stacking TMR junctions in the vertical direction (perpendicular to the film plane) rather than only using in-plane magnetization. The second TMR junction has magnetization oriented perpendicular to the film plane, creating a three-dimensional magnetization configuration that enables additional storage states
2Reliability
If MRAM uses large switching currents to reverse magnetization, then data recording is reliable, but memory integration scale is limited
Solution Approach 1:
The patent applies different magnetization orientations and switching characteristics to different regions (first and second TMR junctions). The first TMR junction has lower switching current for in-plane magnetization reversal while the second TMR junction has higher switching current for perpendicular magnetization reversal, creating local quality differences that enable reliable multilevel storage
Solution Approach 2:
The patent changes the magnetization orientation parameter from in-plane to perpendicular between the two TMR junctions. This parameter change results in different switching current thresholds, allowing the system to distinguish between multiple data levels (0, 1, 2, 3) based on the current required for magnetization reversal
3Productivity
If MRAM records multilevel data in single cell, then integration density increases, but switching current thresholds must be precisely controlled
Solution Approach 1:
The patent segments the magnetization control into two independent TMR junctions with different magnetization orientations. This segmentation allows independent optimization of switching current thresholds for each junction, making it easier to achieve precise control for multilevel data storage (0, 1, 2, 3 levels) without requiring extremely tight manufacturing tolerances across the entire structure
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 multilevel data storage in a single cell, reducing the required switching currents and allowing for smaller cell sizes, thereby increasing memory scale and integration density while maintaining reliable data recording and reading capabilities.
Implementation Method 1
a magnetic tunnel junction exhibiting tunneling magnetoresistive effect
Implementation Method 2
the magnetization direction in the free layer is reversed by spin transfer through current injection
Data Source
AI summary
A first magnetic layer has a magnetization fixed along one direction. A first nonmagnetic layer on the first magnetic layer functions as a first tunnel barrier. A second magnetic layer on the first nonmagnetic layer has a magnetization whose direction can be reversed by spin transfer current injection. A second nonmagnetic layer on the second magnetic layer functions as a second tunnel barrier. A third magnetic layer on the second nonmagnetic layer has a magnetization whose direction can be reversed by spin transfer through current injection at a current density different from the second magnetic layer. First magnetic, first nonmagnetic layer, and second magnetic layers exhibit a first magnetoresistive effect. Second magnetic, second nonmagnetic, and third magnetic layers exhibit a second magnetoresistive effect. A magnetoresistive effect element records and reads out data of at least three levels based on a synthetic resistance from the first and second magnetoresistive effects.