Memory Controller Degradation Compensation for Read Pass Probability
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Solution Overview
Problem
Non-volatile memory devices face challenges in maintaining data integrity due to degradation over time, leading to errors in read operations, as the threshold voltage distributions of memory cells change with retention time, program states, and interference from adjacent cells, which existing technologies fail to adequately address through standard read voltage settings.
Innovation Solution
A memory controller and storage device system that calculates a degradation compensation level using weight and offset tables, along with a displacement level, to adjust the read voltage, performing a history read operation with a history read voltage set when the default read operation fails, and searching for an optimal read voltage set when necessary to improve read pass probability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a default read voltage set is used for reading data from non-volatile memory, then the read operation is simple and fast, but the read pass probability decreases over time due to memory degradation and threshold voltage shifts
Solution Approach 1:
The patent implements dynamic read voltage adjustment by switching between a default read voltage set for normal operations and a history read voltage set or optimal read voltage set when degradation is detected. The read manager dynamically selects appropriate voltage sets based on read operation results, allowing the system to adapt to memory degradation over time while maintaining fast read speeds for healthy memory cells.
Solution Approach 2:
The patent changes the read voltage parameter based on memory degradation state. By calculating degradation compensation levels and adjusting read voltages accordingly (either through history read voltage sets derived from previous optimal voltages or through optimal read voltage search), the system compensates for threshold voltage shifts caused by degradation, thereby maintaining high read pass probability without sacrificing the simplicity and speed of default read operations.
2Reliability
If read voltage is adjusted to compensate for degradation, then the read pass probability increases, but the system complexity increases due to additional voltage calculation and management mechanisms
Solution Approach 1:
The patent performs preliminary actions by maintaining history read voltage sets that are pre-calculated based on previous optimal read voltages and degradation compensation levels. When a read operation fails with the default voltage set, the system can immediately try the pre-computed history read voltage set without performing a full optimal voltage search, thereby reducing the complexity of real-time voltage management while still achieving high read pass probability.
Solution Approach 2:
The read manager acts as an intermediary that manages multiple read voltage sets (default, history, and optimal) and selects the appropriate set based on read operation results. This intermediary component simplifies the overall system architecture by centralizing voltage selection logic and avoiding the need for complex distributed voltage management across multiple controllers.
3Reliability
If an optimal read voltage set is searched for when degradation occurs, then the read pass probability is maximized, but the time required for read operations increases
Solution Approach 1:
The patent performs preliminary action by pre-calculating and storing history read voltage sets based on previous optimal read voltage searches and degradation compensation levels. When degradation is detected and the default read voltage fails, the system can immediately use the pre-computed history read voltage set without initiating a time-consuming optimal voltage search, thereby maintaining high read pass probability while minimizing additional read operation time.
Solution Approach 2:
The patent applies partial action by performing a full optimal read voltage search only when necessary (when both default and history voltage sets fail), rather than continuously. For most read operations, the system uses the simpler default or history voltage sets, performing the exhaustive optimal search only as a fallback mechanism, thus balancing read pass probability with operation time efficiency.
Data Source
AI summary
An operating method of a storage device including a memory controller and a non-volatile memory, the method including: performing a first read in response to a read request by reading data from the non-volatile memory using a default read voltage set; and performing a second read when the first read fails, by calculating a degradation compensation level, using a weight table, offset table, and displacement level, calculating a history read voltage set by performing an operation on the default read voltage set and degradation compensation level, and reading the data using the history read voltage set, wherein the weight table includes weights preset according to word line groups and state read voltages, the offset table includes offset levels preset according to the word line groups and the state read voltages, and the displacement level corresponds to a difference between a default read voltage level and an optimal read voltage level.