Nonvolatile Memory Controller Flag Cell Voltage Adjustment
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Solution Overview
Problem
Data storage devices with semiconductor memory face challenges in reliably recovering from power failures, as they often leave program operations incomplete, leading to data integrity issues and reduced storage device reliability.
Innovation Solution
A data storage device with a nonvolatile memory device and a controller that adjusts the read voltage for flag cells to determine the last programmed page and complete interrupted operations, ensuring reliable recovery from power failures by identifying and managing the most significant bit (MSB) pages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a power failure occurs during a program operation, then the program operation is interrupted and data integrity is compromised, but adjusting the read voltage for flag cells and identifying the last programmed page enables reliable recovery and completes the interrupted operation
Solution Approach 1:
The patent applies preliminary action by setting flag cells to a specific state (programmed or erased) before the actual data programming operation begins. This preliminary flag setting creates a recoverable state that allows the system to identify the last successfully programmed page after a power failure. The flag cells serve as a preliminary marker that enables outage restoration without data loss.
Solution Approach 2:
The patent implements feedback by reading the flag cell states after power restoration to determine which pages were successfully programmed before the power failure. The controller uses this feedback information about flag cell states to identify the last programmed page and decide whether to complete the interrupted programming operation or skip it, thereby ensuring data integrity while restoring reliability.
2Measurement precision
If the read voltage for flag cells is adjusted based on the last programmed page identification, then accurate detection of MSB pages is achieved, but the complexity of the recovery operation increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the read voltage applied to flag cells based on the identified last programmed page. When the last programmed page is determined to be an MSB page, the controller changes the read voltage parameter to an adjusted level that enables accurate detection of the flag cell states. This parameter change improves measurement precision while the automated nature of the process minimizes the perceived complexity.
Solution Approach 2:
The patent implements dynamics by making the read voltage for flag cells adaptive rather than fixed. The system dynamically adjusts the read voltage based on the operational context (whether the last programmed page is an MSB page or not). This dynamic adjustment allows the system to optimize measurement precision for different scenarios while maintaining a unified recovery procedure that doesn't significantly increase operational complexity.
Data Source
AI summary
A method for operating a data storage device using, as a storage medium, a nonvolatile memory device including a memory cell array which is constructed by pages including data cells and flag cells for storing whether upper bit (MSB) data is stored in a data cell, includes searching a last programmed page in the case where recovery is made from a power failure to a normal state; determining whether the last programmed page is an upper bit (MSB) page to be accessed to store upper bit (MSB) data; and adjusting a flag cell read voltage for reading flag cells, in the case where the last programmed page is an upper bit (MSB) page.