Memory Controller Read Voltage Adjustment for Data Reliability
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Solution Overview
Problem
Threshold voltage variations in flash memory devices due to factors like floating gate coupling and charge loss lead to unreliable read data, particularly with uncorrectable error bits, which deteriorate the reliability of nonvolatile memory devices.
Innovation Solution
A method involving a memory controller that reads data using both a first and a second read voltage, corrects error bits using an ECC decoder, and reprograms data based on the comparison result, improving data reliability by shifting threshold voltage distributions back to their original state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single read voltage is used to read data from nonvolatile memory, then the read operation is simple and fast, but threshold voltage variations cause uncorrectable error bits that deteriorate data reliability
Solution Approach 1:
The read operation is segmented into multiple stages: first read data using initial read voltage, then read again using adjusted read voltage when uncorrectable errors are detected. This segmentation allows the system to maintain simplicity for normal operations while enhancing reliability when needed.
Solution Approach 2:
The read voltage parameter is dynamically changed based on error detection results. When uncorrectable error bits are detected in the first read operation, the read voltage is adjusted (increased or decreased) for the second read operation to compensate for threshold voltage variations and retrieve correct data.
2Reliability
If read voltage is adjusted to correct error bits, then data reliability improves, but additional read operations increase time consumption
Solution Approach 1:
The system performs a second read operation with adjusted voltage only partially - specifically when uncorrectable error bits are detected in the first read. This conditional approach ensures that the time-consuming retry operation is executed only when necessary, minimizing time loss while maintaining reliability.
Solution Approach 2:
The system uses error detection feedback from the first read operation to determine whether to perform the second read operation. The ECC decoder's detection of uncorrectable error bits triggers feedback to the controller, which then decides to adjust read voltage and perform another read, creating a closed-loop control system that balances speed and reliability.
3Reliability
If threshold voltage variations are allowed to accumulate, then device operation remains simple, but data integrity deteriorates over time
Solution Approach 1:
The system performs preliminary error detection using ECC decoding after the first read operation. This preliminary action identifies uncorrectable error bits before final data usage, allowing the system to trigger a corrective second read operation with adjusted voltage to prevent using corrupted data.
Solution Approach 2:
The patent replaces complex continuous threshold voltage compensation mechanisms with a discrete error detection and correction system using ECC codes and conditional voltage adjustment. Instead of continuously monitoring and adjusting voltages, the system uses digital error detection and triggers voltage adjustment only when errors are detected, simplifying the overall mechanism.
Data Source
AI summary
A method of operating a memory controller, a memory controller, a memory device and a memory system are provided. The method includes reading first data from a nonvolatile memory device using a first read voltage, the first data includes a uncorrectable error bit, reading second data from a nonvolatile memory device using a second read voltage different from the first read voltage, the second data includes an correctable error bit, and reprogramming the nonvolatile memory device according to the comparison result of the first read voltage and the second read voltage.