Analog Memory Cell Read Accuracy via Modified Pass Voltages
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Solution Overview
Problem
Existing memory devices face challenges in accurately reading data from analog memory cells, particularly when threshold voltages drift over time, leading to read errors due to the high pass voltages used during programming verification, which can result in unselected cells stopping conductance and distorting the read operation.
Innovation Solution
The method involves applying lower pass voltages during data readout than those used during programming verification, selectively reducing voltages only to unselected cells that are unlikely to affect conductance, and setting pass voltages based on the storage value range of other memory cells to improve read accuracy and reduce cross-coupling interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high pass voltages are used during programming verification, then programming accuracy is improved, but unselected cells stop conductance and distortion of read operation occurs
Solution Approach 1:
The patent segments the memory array into selected cells and unselected cells, applying different voltage levels to each segment. Selected cells receive high pass voltages for accurate programming verification, while unselected cells receive lower pass voltages to maintain conductance and avoid distortion.
Solution Approach 2:
The patent applies local quality by providing different voltage conditions to different spatial locations in the memory array. High pass voltages are applied locally to selected cells for accurate verification, while lower pass voltages are applied locally to unselected cells to prevent conductance stopping and distortion.
2Measurement precision
If high pass voltages are applied to all cells, then selected cells can be verified accurately, but unselected cells are affected and read accuracy decreases
Solution Approach 1:
The patent segments the voltage application strategy by identifying which cells are selected and which are unselected, then applying appropriate voltage levels to each segment. This segmentation eliminates cross-coupling interference from unselected cells while maintaining verification accuracy for selected cells.
Solution Approach 2:
The patent changes the voltage parameter dynamically based on cell selection status. High pass voltages are used for selected cells during verification, while lower pass voltages are used for unselected cells during read operations, optimizing both verification accuracy and read accuracy by eliminating harmful cross-coupling effects.
3Reliability
If pass voltages are reduced for unselected cells, then read errors are reduced, but programming verification may be affected
Solution Approach 1:
The patent segments the voltage application by cell selection status, ensuring that reduced pass voltages for unselected cells do not affect programming verification of selected cells. The verification process uses high pass voltages on selected cells while unselected cells use lower voltages, maintaining both read reliability and verification accuracy.
Solution Approach 2:
The patent applies local quality by providing high pass voltages locally to selected cells during verification and lower pass voltages locally to unselected cells during read operations. This localized voltage application ensures that read reliability is improved without compromising verification accuracy of the selected cells.
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 reliability of data readout by shifting threshold voltage distributions, allowing for accurate differentiation between programming levels and reducing the probability of read errors, even when threshold voltages become negative, while maintaining minimal impact on unselected cells' conductance.
Implementation Method 1
threshold voltages drift over time, leading to read errors
Implementation Method 2
high pass voltages used during programming verification, which can result in unselected cells stopping conductance and distorting the read operation
Data Source
AI summary
A method for data storage includes storing data in a target analog memory cell, which is one of a group of analog memory cells that are connected in series with one another, by writing a storage value into the target memory cell. The storage value written into the target memory cell is verified while biasing the other memory cells in the group with respective first pass voltages. After writing and verifying the storage value, the storage value is read from the target memory cell while biasing the other memory cells in the group with respective second pass voltages, wherein at least one of the second pass voltages applied to one of the other memory cells in the group is lower than a respective first pass voltage applied to the one of the other memory cells. The data is reconstructed responsively to the read storage value.