Flash Memory Read Voltage Adjustment for Coupling Effect Reduction
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Solution Overview
Problem
Conventional multi-level cell (MLC) flash memory experiences increased bit error rates due to coupling effects between neighboring pages, which can lead to overlapping threshold voltage distributions and errors that are not correctable by traditional error correction controls.
Innovation Solution
The method involves reading a neighboring page multiple times using distinct read voltages and transferring the threshold-voltage distributions to cancel or reduce coupling effects by shifting the rightmost or leftmost parts of the distributions, using a flag to determine the necessary shifts based on read data and voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional MLC flash memory uses constant read voltages, then the reading operation is simple and fast, but threshold voltage distributions overlap due to coupling effects causing increased bit error rates
Solution Approach 1:
The patent applies dynamics by making the read voltage variable rather than constant. The system dynamically adjusts read voltages based on detected threshold voltage distributions and coupling effects from neighboring pages. Multiple read voltages are applied in sequence to different pages, allowing the reading operation to adapt to changing conditions and reduce bit error rates caused by distribution overlap.
Solution Approach 2:
The patent implements preliminary action by performing read operations on neighboring pages before reading the target page. This preliminary reading allows the system to detect and characterize coupling effects that will affect the target page reading. By anticipating and preparing for coupling effects in advance, the system can adjust subsequent read voltages to compensate for expected interference.
2Reliability
If multiple read voltages are applied to compensate for threshold voltage shifts, then bit error rate is reduced, but the reading process becomes more time-consuming
Solution Approach 1:
The patent applies segmentation by dividing the reading process into distinct stages: preliminary reading of neighboring pages, detection of threshold voltage distributions, identification of coupling effects, and then targeted reading of the target page with adjusted voltages. This segmented approach allows the system to apply multiple voltages only where necessary rather than uniformly to all pages, reducing overall reading time while maintaining data accuracy.
Solution Approach 2:
The patent implements local quality by applying different read voltages to different pages based on their specific coupling conditions. Rather than using a uniform voltage adjustment across all pages, the system tailors the read voltage to each page's local characteristics and interference level. This allows optimized reading where needed while maintaining fast reading where interference is minimal.
Data Source
AI summary
A method of reducing coupling effect in a flash memory is disclosed. A neighboring page is read, and a flag is set active if the neighboring page is an interfering page. Data are read from the neighboring page at least two more times using at least two distinct read voltages respectively. The threshold-voltage distributions associated with an original page and the neighboring page are transferred according to the read data and the flag.