Series-Connected MTJ Storage Element for Multi-Bit Density
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Solution Overview
Problem
Current magneto-resistive random access memory (MRAM) devices face challenges in scaling down to store multi-bit data effectively, as traditional single-bit storage methods become inefficient with miniaturization.
Innovation Solution
A magneto-resistive storage element comprising two unit devices (MTJ1 and MTJ2) connected in series, with each unit having a pinned layer, tunnel insulating layer, and free layer, where the magnetic polarity of the free layers changes in response to different current amounts, allowing for four distinct resistance values and enabling the storage of 2-bit data in a single storage element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional single-bit storage methods are used in MRAM devices, then the device structure is simple, but the storage density and scalability deteriorate when scaling down to store multi-bit data
Solution Approach 1:
The magnetic storage element is divided into multiple magnetic units (first magnetic unit and second magnetic unit) connected in series, where each unit can independently store one bit of data. This segmentation allows the device to store multi-bit data (e.g., 2-bit) in a single storage element, thereby improving storage density without requiring proportionally more storage elements, and maintaining scalability when scaling down.
2Quantity of substance
If multiple memory cell units are used to store multi-bit data, then the storage capacity is sufficient, but the device area increases reducing scalability
Solution Approach 1:
Multiple magnetic units (first magnetic unit and second magnetic unit) are merged into a single magnetic storage element connected in series. Each unit contains pinned layers, tunnel insulating layers, and free layers that can be independently controlled. This merging allows multi-bit data storage within one compact storage element, significantly reducing the device area compared to using separate memory cell units for each bit, thus improving scalability.
3Quantity of substance
If the magnetic storage element uses different current amounts to change magnetic polarity, then multi-bit data can be stored, but the control complexity increases
Solution Approach 1:
Different free layers (first free layer and second free layer) are designed with different magnetic properties, specifically different switching current thresholds. The first free layer switches magnetic polarity at a first current amount, while the second free layer switches at a second current amount (higher than the first). This local differentiation in magnetic properties enables independent control of each magnetic unit through current amount modulation, allowing multi-bit data storage without requiring complex control circuitry.
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 allows for the efficient storage and retrieval of 2-bit data in a reduced area, enhancing the scalability and density of MRAM devices by utilizing different current amounts to alter magnetic directions and resistance states within the storage elements.
Implementation Method 1
When electrons passing through a first ferromagnetic layer enter an insulating layer serving as a tunneling barrier, electron's probability to penetrate into the insulating layer is determined by a magnetic direction of second ferromagnetic layer
Implementation Method 2
an MRAM device is a non-volatile memory device where data is stored by magnetic storage elements having different resistance states according to magnetic field changes between ferromagnetic plates
Data Source
AI summary
A magneto-resistance memory device includes a first pinned layer having a first magnetic polarity regardless of current applied to the first pinned layer, a first tunnel insulating layer arranged on the first pinned layer, a first free layer arranged on the first tunnel insulating layer and having a magnetic polarity that changes in response to current of a first amount, a second pinned layer coupled to the first free layer and having the first magnetic polarity regardless of current applied to the first pinned layer, a second tunnel insulating layer arranged on the second pinned layer, a second free layer arranged on the second tunnel insulating layer and having a magnetic polarity that changes in response to current of a second amount, wherein the second amount is smaller than the first amount, and a connection layer.