Resistive Cross-Point Memory Read Circuit Using Dual Reference Currents
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Solution Overview
Problem
The reliability of determining data in a resistive cross-point cell array is impaired by sneak path currents, which hinder accurate resistance detection due to the presence of parallel paths, and existing methods require precise potential equalization or multiple dummy cells to mitigate this issue.
Innovation Solution
The use of two different reference currents or reference cells with distinct resistance values to compare the current differences between the selected cell and each reference, effectively suppressing the influence of sneak path currents and improving data determination accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a cross-point cell array is used for high-density integration, then integration density is improved, but sneak path currents increase and hinder accurate resistance detection
Solution Approach 1:
The patent segments the current measurement process into multiple discrete current levels (first current level and second current level) rather than using a single measurement. This segmentation allows the system to distinguish between sneak path currents and actual memory cell currents by comparing measurements at different current levels, thereby resolving the contradiction between high integration density and reliable data determination.
Solution Approach 2:
The patent changes the current level parameter during the read operation by applying different current levels (first current level and second current level) to the selected bit line. This parameter change enables the system to differentiate between parasitic sneak path currents and the resistance signal from the memory cell, improving data determination reliability while maintaining high integration density.
2Measurement precision
If precise potential equalization is applied to suppress sneak path currents, then measurement precision is improved, but device complexity increases
Solution Approach 1:
Instead of precisely controlling potentials to be equal (which would increase device complexity), the patent changes the current level parameter to two distinct levels. This approach achieves accurate resistance detection by comparing measurements at different current levels, avoiding the need for complex potential equalization control circuits.
Solution Approach 2:
The patent replaces the mechanical/electrical control approach of precise potential equalization with a measurement-based approach using multiple current levels. This substitution simplifies the control system while achieving the same goal of suppressing sneak path current influence on measurements.
3Measurement precision
If dummy cells are used to remove offset components, then measurement precision is improved, but device complexity and area increase
Solution Approach 1:
The patent uses parameter changes (applying different current levels) to achieve offset removal without requiring additional dummy cells. By measuring at two different current levels and comparing the results, the system can mathematically eliminate the offset component caused by sneak path currents, improving signal-to-noise ratio without increasing device complexity or area.
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 allows for reliable data determination in the presence of sneak path currents without the need for precise potential control or numerous dummy cells, enhancing the signal-to-noise ratio and reducing erroneous reads.
Implementation Method 1
The direction of magnetization has an influence on the resistance of a memory cell as in a spin-dependent tunnel junction device. For example, when the direction of magnetization is parallel, the resistance of a memory cell has a first value R, and when the direction of magnetization is changed from 'parallel' to 'reverse parallel’, the resistance of the memory cell increases to a second value R+ΔR.
Data Source
AI summary
In order to determine data stored in a memory cell of a resistive cross-point cell array, two reference cells having two different known resistance values (e.g., data “0” and data “1”) are provided, and a difference in current between a selected cell and the reference cell having data “0” and a difference in current between the selected cell and the reference cell having data “1” are compared. By comparison with a current of the reference cell which has a parasitic current as with the selected cell and has known data “0”/“1”, data can be determined while suppressing an influence of a parasitic current.