Nonvolatile Memory Controller Time-After-Erase Compensation
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Solution Overview
Problem
The reliability of nonvolatile semiconductor memory devices is compromised due to extended periods of time during which memory cells are left unprogrammed after erasure, leading to decreased performance and accuracy in data storage and retrieval.
Innovation Solution
Implementing an operating method for storage devices that involves reading previously programmed memory cells to determine the time after erase, programming meta data indicative of this time, and using this information to manage and compensate for the time elapsed since erasure, thereby improving memory cell reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If memory cells are left unprogrammed after erasure for extended periods, then device complexity is reduced by not requiring immediate programming, but reliability deteriorates due to degraded performance and accuracy
Solution Approach 1:
The patent performs preliminary detection of the time after erase by reading previously programmed memory cells before programming the selected memory cells. This preliminary action allows the system to know the elapsed time in advance and program appropriate compensation metadata, thereby preventing reliability degradation before it occurs rather than reacting to it afterward.
Solution Approach 2:
The system implements a feedback mechanism where the detected time after erase information is used to determine compensation metadata that is then programmed into the memory cells. This closed-loop feedback ensures that the programming operation accounts for the elapsed time, maintaining reliability even when memory cells remain unprogrammed for extended periods.
2Reliability
If the storage device performs read operations to detect time after erase, then memory cell reliability is improved through compensation, but loss of time occurs due to additional read operations during idle state
Solution Approach 1:
The patent utilizes the memory cells themselves to store and provide the time after erase information by reading previously programmed cells. The memory structure serves its own timing detection function, eliminating the need for separate external timing circuits or mechanisms, thereby reducing overall system complexity while maintaining accuracy.
Solution Approach 2:
The system performs the time detection read operations during idle states when the storage device is not actively servicing host requests. This continuity approach ensures that reliability compensation data is always available without interrupting productive operations, effectively utilizing otherwise wasted time periods.
3Manufacturing precision
If compensation metadata is programmed based on detected time after erase, then manufacturing precision is improved through accurate time tracking, but device complexity increases due to metadata programming operations
Solution Approach 1:
The patent uses the existing metadata programming capability of the storage device for multiple purposes: it programs both the user data and the time after erase compensation metadata using the same programming circuitry and control logic. This multi-functionality approach avoids adding dedicated hardware for metadata programming, thereby limiting the increase in device complexity.
Solution Approach 2:
The system merges the time detection and metadata programming operations into a single integrated process. The detected time after erase information is immediately used to generate and program compensation metadata in the same operational sequence, combining what could be separate functions into one unified operation that reduces overall complexity.
Data Source
AI summary
A storage device includes a nonvolatile memory having a plurality of memory cells and a memory controller to control the nonvolatile memory. The operating method of the storage device includes reading previously programmed memory cells among the memory cells of the nonvolatile memory and determining a time after erase of the previously programmed memory cells, programming selected memory cells of the nonvolatile memory, and programming meta data including a time after erase of the selected memory cells, based on the determined time after erase of the previously programmed memory cells.