Stacked MTJ MRAM Sensing Margin via Vertical Segmentation
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Solution Overview
Problem
Magnetic random access memory (MRAM) devices face challenges with a small on/off resistance ratio, leading to decreased sensing margin and reliability, especially as integration increases, resulting in overlapping cell distributions and reduced array sizes.
Innovation Solution
The implementation of a magnetic random access memory (MRAM) with two independently stacked magnetic tunnel junctions (MTJs) that share a common stack structure, allowing for simultaneous application of currents in opposite directions to achieve increased sensing margin without expanding the memory cell area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single MTJ structure is used, then the device complexity is low, but the sensing margin is small due to small on/off resistance ratio
Solution Approach 1:
The storage node is segmented into two independent MTJs (first MTJ and second MTJ) that are sequentially stacked. Each MTJ can independently store one bit of data, allowing the system to achieve doubled sensing margin by comparing resistance differences across both MTJs while maintaining manageable device complexity through modular stacking
Solution Approach 2:
The patent transitions from a planar single-MTJ structure to a vertically stacked two-MTJ structure. By stacking the first and second MTJs sequentially in the vertical dimension, the invention doubles the sensing margin without increasing the lateral cell area, effectively using the vertical dimension to resolve the contradiction between sensing margin and device complexity
2Productivity
If the degree of integration increases, then the array size can be reduced, but the resistance increases causing sensing margin to decrease
Solution Approach 1:
By stacking two MTJs vertically to form a single storage node, the invention doubles the sensing margin through vertical integration without increasing lateral footprint. This allows higher integration density while maintaining or improving sensing margin, as the vertical stacking approach efficiently uses three-dimensional space
3Reliability
If two independently stacked MTJs are used, then the sensing margin is doubled, but the manufacturing process becomes more complex
Solution Approach 1:
The manufacturing process is segmented into sequential steps where the first MTJ is formed, then a conductive pad layer is deposited, and finally the second MTJ is formed on top. This segmented approach allows each MTJ to be manufactured using standard processes while achieving the benefit of doubled sensing margin through vertical stacking
Solution Approach 2:
The conductive pad layer is formed preliminarily between the first and second MTJs to establish electrical connections before the second MTJ is completed. This preliminary action simplifies the overall manufacturing process by preparing connection paths in advance, reducing the complexity of integrating two independent MTJs into a functional storage node
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 doubles the sensing margin compared to conventional methods, enabling reliable data reading and writing while maintaining a compact memory cell size.
Implementation Method 1
A magnetic random access memory (MRAM) is a random access memory (RAM) that reads data written on a magnetic tunnel junction (MTJ) by measuring a resistance difference from magnetization states of a free layer and a pinned layer
Implementation Method 2
A magnetization direction of the free layer may change when a magnetic field having a set (or, predetermined) intensity is applied to the free layer
Implementation Method 3
A magnetization direction of the free layer may change depending on a spin state of an electric current flowing through the MTJ
Implementation Method 4
A resistance measured when magnetization directions of the free layer and the pinned layer are the same is called an 'on' resistance, and a resistance measured when magnetization directions of the free layer and the pinned layer are the opposite is called an 'off' resistance
Implementation Method 5
The switching element may be a field effect transistor
Data Source
AI summary
A magnetic random access memory (MRAM), and methods of manufacturing and operating the MRAM, include a switching element and a storage node connected to the switching element, and a magnetic node configured to simultaneously store two opposite bits.