Flash Memory Mapping Table Update Timing After Migration
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Solution Overview
Problem
Flash memory devices face issues with 'initial verify shift' (IVS) phenomenon, where charge carrier rearrangement leads to threshold voltage shifts, causing data loss and read errors, especially in charge trap flash memory cells used in 3D memory cell arrays.
Innovation Solution
A method is introduced to manage the update of a mapping table in flash memory systems after a migration operation, where data is moved from a buffer region to a main region, with a specific timing to account for the IVS phenomenon, ensuring accurate address updates and reducing read errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If data is immediately moved from buffer region to main region using migration operation, then storage efficiency is improved, but initial verify shift phenomenon causes threshold voltage shifts and data loss
Solution Approach 1:
The patent applies preliminary action by waiting for a predetermined time period after the migration operation before updating the mapping table. This time delay allows the initial verify shift phenomenon to complete its course, preventing threshold voltage shifts from causing data loss. The mapping table update is postponed until after the IVS phenomenon has stabilized, ensuring data integrity while maintaining storage efficiency through the migration operation.
2Measurement precision
If mapping table is updated immediately after migration operation, then address accuracy is improved, but read errors occur due to threshold voltage shifts from IVS phenomenon
Solution Approach 1:
The patent applies preliminary anti-action by introducing a time delay that counteracts the harmful IVS phenomenon. By waiting for the predetermined time period before updating the mapping table, the system allows the threshold voltage to stabilize and prevents the IVS-induced shifts from corrupting the address mapping data. This preliminary waiting period neutralizes the harmful effect of IVS on read operations.
3Productivity
If migration operation is performed frequently to optimize storage, then storage performance is improved, but IVS phenomenon occurs more often causing data loss
Solution Approach 1:
The patent applies preliminary action by implementing a mandatory waiting period after each migration operation before the mapping table can be updated. This preliminary delay ensures that regardless of how frequently migration operations are performed, the IVS phenomenon has time to complete and stabilize, preventing data loss from threshold voltage shifts while maintaining optimal storage performance through frequent migrations.
Data Source
AI summary
A method of operating a memory system includes; storing data in a buffer region of the nonvolatile memory, later issuing a migration request directed to the data stored in the buffer region and executing a migration operation to move the data from buffer region to a main region of the nonvolatile memory device. Upon completion of the migration operation, marking a migration operation completion time, and after an initial verify shift (IVS) time has elapsed following the migration operation completion time, updating a mapping table associated with the data in view of the executed migration operation.