Memory Controller Detection of Degraded Flash Memory Pages
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Solution Overview
Problem
Nonvolatile memory devices, such as flash memory devices, experience reliability issues due to charge loss over time, leading to threshold voltage changes and data errors, which affect the accuracy of read data.
Innovation Solution
A method for operating a memory controller that detects degraded pages in a memory device, counts the number of degraded pages, and recharges or reclaims the affected block based on reference values, using techniques like error bit correction and varying read voltages to determine page degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If charge loss over time is allowed to occur in nonvolatile memory devices, then manufacturing simplicity is maintained, but data reliability deteriorates due to threshold voltage changes
Solution Approach 1:
The memory controller performs preliminary detection of degraded pages by reading data and comparing it with reference data before complete failure occurs. By detecting threshold voltage changes and charge loss early in the degradation process, the system can take preventive recharge operations to restore memory cells before data reliability is severely compromised.
Solution Approach 2:
The system implements feedback by continuously monitoring read data quality and comparing it against reference values. When degradation is detected through repeated reads showing consistent errors, the controller adjusts its operation by triggering recharge operations or replacing affected blocks, creating a closed-loop system that adapts to memory degradation.
2Reliability
If multiple read operations are performed to detect degraded pages, then data reliability is improved through error detection, but time consumption increases
Solution Approach 1:
Instead of performing exhaustive read operations on all memory pages, the system applies partial action by selectively reading only specific pages that show signs of degradation. The controller uses reference data comparison to identify problematic pages and focuses detection efforts only on those areas, avoiding unnecessary time-consuming reads of healthy memory regions.
3Manufacturing precision
If degraded pages are not addressed, then device complexity is minimized, but manufacturing precision of data integrity deteriorates
Solution Approach 1:
The memory device is segmented into individual pages that can be independently detected and managed. The controller identifies specific degraded pages within larger blocks and performs targeted recharge operations on only those affected pages rather than entire blocks. This segmentation allows precise management of data integrity while minimizing the complexity of managing all memory regions uniformly.
Data Source
AI summary
A method of operating a memory controller includes reading data from a first block of a memory device; detecting degraded pages from a plurality of pages of the first block and counting a number of the degraded pages in the first block; and recharging or reclaiming the first block, which includes the degraded pages, based on the counted number of the degraded pages.