Flash Memory Reclaim Control Using Optimal Read Voltage
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Solution Overview
Problem
Nonvolatile memory devices face challenges in maintaining data reliability due to uncorrectable errors caused by reduced read margins and physical disturbances, which existing error correction codes cannot fully address, leading to potential degradation of memory pages.
Innovation Solution
A method is introduced where a recovery read operation is performed using an optimal read voltage determined based on the first data with uncorrectable errors, and the decision to reclaim a memory page is made based on threshold voltage distributions of memory cells, preventing the page from becoming uncorrectable.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multi-level cell flash memory is used to increase storage capacity, then storage capacity is improved, but read margin is reduced causing uncorrectable errors
Solution Approach 1:
The patent performs a recovery read operation using an optimal read voltage determined based on the first data before the memory page is fully degraded. This preliminary action detects threshold voltage distributions of memory cells in a region of interest adjacent to the optimal read voltage, allowing early identification of pages that may become uncorrectable, enabling proactive reclaim operations to maintain data reliability while preserving storage capacity
Solution Approach 2:
The patent changes the read voltage parameter by determining an optimal read voltage specifically for pages with uncorrectable errors, rather than using a fixed read voltage. This parameter change allows the system to adapt to varying memory cell threshold voltage distributions, improving the ability to detect and reclaim degraded pages before they cause data loss, thus maintaining reliability in high-capacity multi-level cell memory
2Reliability
If error correction code operation is performed to correct errors, then error correction capability is improved, but degraded memory cells cannot be detected when no errors remain after ECC
Solution Approach 1:
The patent performs a preliminary recovery read operation using an optimal read voltage determined from the first data before relying solely on ECC correction. This preliminary action examines threshold voltage distributions of memory cells in a region of interest, enabling detection of degraded memory cells even when ECC successfully corrects the errors, thus improving degradation detection accuracy without compromising error correction capability
Solution Approach 2:
The patent introduces an intermediary detection mechanism that examines threshold voltage distributions of memory cells in a region of interest adjacent to the optimal read voltage. This intermediary step acts as a supplement to ECC correction, providing additional information about memory cell degradation that ECC alone cannot detect, thereby improving measurement precision while maintaining error correction capability
3Reliability
If reclaim operation is performed on all pages with errors to prevent degradation, then data reliability is improved, but performance is reduced due to excessive reclaim operations
Solution Approach 1:
The patent applies local quality by examining threshold voltage distributions of memory cells specifically in a region of interest adjacent to the optimal read voltage, rather than uniformly processing all pages. This localized approach identifies only those pages with threshold voltage distributions indicating future uncorrectable errors, enabling selective reclaim operations that maintain data reliability while avoiding unnecessary reclaim operations on healthy pages, thus preserving memory performance
Data Source
AI summary
In a method of controlling reclaim of a nonvolatile memory device including a plurality of memory blocks, wherein each of the memory blocks includes a plurality of pages, a recovery read operation is performed on first data using an optimal read voltage determined based on the first data, when the first data includes errors which are not correctable, wherein the first data is read from a first page of a first memory block of the memory blocks, and, when the errors of the first data are corrected after the recovery read operation is performed, whether to perform a reclaim of the first page is determined based on threshold voltage distributions of memory cells of the first page, wherein the memory cells are disposed in a region of interest adjacent to the optimal read voltage.