NAND Flash Read-Retry Threshold Tuning for Retention Errors
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Solution Overview
Problem
NAND flash devices face challenges in accurate data reading due to factors like data retention and read disturbance, which hinder efficient data retrieval, as they require reading complete pages and are not capable of random access like NOR flash devices.
Innovation Solution
A data storage device with a controller that performs a default read operation using a default read threshold voltage, and upon failure, sequentially attempts read operations using different read threshold voltages from a read-retry table to ensure successful data retrieval, adapting to varying conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a default read threshold voltage is used for reading data from NAND flash memory, then the read operation is simple and fast, but read failures occur due to data retention issues and read disturbance
Solution Approach 1:
The patent pre-configures multiple read threshold voltage values in a read-retry table before actual read operations. When a read failure occurs, the controller sequentially tries different threshold voltages from the pre-configured table without needing complex real-time analysis, thus improving reliability while keeping the retry mechanism relatively simple
Solution Approach 2:
The patent changes the read threshold voltage parameter systematically through multiple retry attempts with different voltage values. By adjusting this critical parameter based on pre-configured tables, the system can adapt to varying memory cell conditions caused by data retention and read disturbance, thereby resolving read failures
2Reliability
If multiple read threshold voltages are tried sequentially upon default read failure, then read reliability improves, but read time increases
Solution Approach 1:
The read-retry table is pre-configured with multiple threshold voltage values and their optimal sequences before actual read operations. This preliminary preparation allows the controller to quickly try the most likely successful threshold voltage first, minimizing the average read time while maintaining high reliability
Solution Approach 2:
The patent implements a sequential retry mechanism that quickly tries different threshold voltages in a predetermined order. The controller rushes through the retry process by systematically attempting each pre-configured threshold voltage without unnecessary delays, thereby reducing the overall time loss while ensuring reliable data retrieval
3Productivity
If the read threshold voltage configuration is updated based on successful read operations, then future read efficiency improves, but controller complexity increases
Solution Approach 1:
The patent implements a feedback mechanism where the controller monitors read operation results and updates the read-retry table accordingly. When a particular threshold voltage successfully retrieves data, this information is fed back to update the configuration, improving future read efficiency. The feedback logic is kept relatively simple by only updating based on clear success/failure outcomes
Solution Approach 2:
The controller performs self-updating of the read-retry table based on its own read operation experiences. By automatically learning from successful and failed read attempts, the system improves its own efficiency without requiring external intervention or complex manual configuration, balancing enhanced productivity with manageable complexity
Data Source
AI summary
A data storage device is provided. The data storage device includes a flash memory and a controller. The flash memory includes a plurality of blocks for storing data and each block includes a plurality of pages. The controller is configured to convert a host read command into a read-operation instruction to the flash memory to perform a default read operation to read page data from the flash memory. The default read operation has a default read threshold voltage. In response to a failure of the default read operation, the controller is configured to sequentially perform a read operation on the flash memory using a read threshold voltage with respect to each entry of a plurality of entries in a read-retry table, and replace the default read threshold voltage with the read threshold voltage corresponding to the read operation being successfully performed.