Storage Controller Read Voltage Adaptation for Degraded Memory Cells
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Solution Overview
Problem
The operational performance of storage devices deteriorates due to read voltage failures resulting from memory cell degradation, leading to unsuccessful read operations.
Innovation Solution
A controller in the storage device performs mutation operations to search for an optimal read voltage by applying offset values to a default read voltage, adjusting the read voltage based on error check node values and fail bit counts to improve read operation success.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a preset read voltage is used for reading data from memory cells, then the read operation can be performed with simple control, but the read operation fails when memory cells degrade leading to deteriorated operational performance
Solution Approach 1:
The read voltage is changed from a fixed preset value to a dynamically adjustable parameter. The controller performs mutation operations that adjust the read voltage based on whether read operations succeed or fail, allowing the system to adapt to memory cell degradation over time while maintaining operational reliability
Solution Approach 2:
The system implements feedback mechanisms where the result of read operations (success or failure) is used to adjust subsequent read voltage selections. When read operations fail, the controller searches for alternative read voltages and uses feedback from these searches to improve future read operations, creating a self-correcting system that maintains high reliability
2Reliability
If the read voltage is adjusted to accommodate memory cell degradation, then the read operation success rate improves, but the control complexity increases due to mutation operations
Solution Approach 1:
The voltage adjustment process is segmented into distinct mutation operations: a first mutation operation that searches for alternative read voltages when read operations fail, and a second mutation operation that performs adjustments when reads succeed. This segmentation allows the complex control logic to be organized into manageable, modular steps that can be implemented systematically
Solution Approach 2:
The controller performs preliminary searches for alternative read voltages using the first mutation operation before actual data read operations are needed. By pre-searching and storing viable alternative voltages, the system reduces the complexity of real-time voltage adjustment during critical read operations, as the decision space has already been explored and narrowed
Data Source
AI summary
A storage device includes a memory including a plurality of word lines, a plurality of bit lines, and a plurality of memory cells; and a controller controlling a read operation on the memory, performing a first mutation operation of searching for a next read voltage using a first candidate read voltage when the read operation fails, and performing a second mutation operation of searching for the next read voltage using a second candidate read voltage when the read operation succeeds. The first candidate read voltage is obtained by applying a first offset value to a default read voltage used in the read operation, and the second candidate read voltage is obtained by applying a second offset value to the default read voltage.