MRAM Cell Selector Structure for Density Scaling
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Solution Overview
Problem
The density of magnetic random access memory (MRAM) structures is limited by the access transistors rather than the memory storage, hindering the scaling of MRAM to smaller geometries due to the dominance of access transistors in the cell area.
Innovation Solution
The implementation of a one selector/one junction (1S1J) MRAM cell architecture, where a bidirectional selector device replaces the access transistor, allowing for more cost-effective fabrication and improved density by using a pMTJ structure coupled with a selector layer that provides nonlinear I-V behavior for reading and switching functions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If access transistors are used in MRAM structures, then the memory can be accessed and controlled, but the cell area is dominated by the access transistors which limits the memory density and scaling to smaller geometries
Solution Approach 1:
The patent extracts the transistor gate from the planar cell area and moves it to a vertical dimension by forming the gate as a three-dimensional structure (such as a FinFET or nanosheet gate) that extends vertically above the pMTJ. This allows the gate control function to be maintained while significantly reducing the footprint area occupied by the access transistor, thereby improving memory density.
Solution Approach 2:
The patent transitions from a two-dimensional planar transistor layout to a three-dimensional vertical structure. The access transistor is configured with a gate that extends in the vertical dimension (z-axis) rather than occupying horizontal space, enabling the cell to scale to smaller geometries while maintaining control functionality.
2Productivity
If the cell area is reduced for higher density, then the memory scaling is improved, but the access transistor dominance becomes more problematic
Solution Approach 1:
The patent merges the access transistor structure with the pMTJ structure by forming the transistor gate to directly contact or be in close proximity to the pMTJ electrode. This integration reduces the overall cell area and simplifies the interconnection structure, allowing higher density without proportionally increasing device complexity.
Solution Approach 2:
The patent forms the access transistor structure and its gate in advance during the fabrication process, integrating it with the pMTJ structure before final assembly. This preliminary formation of the three-dimensional gate structure enables subsequent reduction of cell area without requiring additional complex processing steps.
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 enhances the density of MRAM cells by reducing the size of the selector device to match the pMTJ structure, enabling higher density memory arrays and improved data storage efficiency without increasing the die area occupied by the access transistor.
Implementation Method 1
a pMTJ structure that stores a data bit
Implementation Method 2
a selector device coupled to an electrode of the pMTJ structure, the selector device providing nonlinear I-V behavior
Data Source
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AI summary
An MRAM cell may include a magnetic tunneling junction (MTJ). The MTJ includes a pin layer, a barrier layer, a free layer, and a capping layer. The MRAM cell further includes a bidirectional diode selector, directly coupled to an electrode of the MTJ, to enable access to the MTJ.