Nonvolatile Memory Read Voltage Adjustment via Cell Counting
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Solution Overview
Problem
The reliability of data stored in charge trap flash memory cells is degraded due to physical characteristics that affect the distribution of threshold voltages, leading to errors in read operations.
Innovation Solution
A method is introduced for operating nonvolatile memory devices that involves receiving a read command, performing a cell counting operation, adjusting read voltages based on a reference voltage, and using a read voltage level lookup table to optimize read operations, thereby reducing errors by adjusting read voltage levels to match the changing threshold voltage distribution over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If charge trap flash memory cells are used for nonvolatile storage, then data retention without power is achieved, but threshold voltage distribution shifts over time causing read errors
Solution Approach 1:
The patent performs a cell counting operation before the actual read operation to determine the current threshold voltage distribution characteristics. This preliminary action allows the system to adjust read voltages in advance based on the counted cell states, compensating for threshold voltage shifts that occur over time during data retention.
Solution Approach 2:
The patent implements a feedback mechanism where the result of the cell counting operation is used to adjust the read voltages. The memory device counts the number of cells in different states, feeds this information back to modify the read voltage levels, and then performs the read operation with the adjusted voltages, thereby maintaining read accuracy despite threshold voltage distribution changes.
2Reliability
If read voltages are adjusted dynamically based on cell counting, then read error rate is reduced, but operation complexity increases
Solution Approach 1:
The patent merges the cell counting operation with the read operation sequence, performing the counting as a preliminary step that informs the subsequent read operation. This integration allows the system to use the counting results directly to adjust read voltages without requiring separate complex calibration procedures, thereby reducing overall operational complexity while maintaining accuracy.
3Measurement precision
If multiple read voltages are used for sensing operations, then measurement precision is improved, but use of energy increases
Solution Approach 1:
The patent applies partial action by adjusting only the necessary read voltages based on the cell counting results, rather than uniformly adjusting all read voltages. The system determines which specific read voltage levels need modification based on the detected threshold voltage distribution, applying energy-efficient adjustments only where needed to maintain measurement precision.
Data Source
AI summary
An method of operating a nonvolatile memory device including a plurality of memory cells comprises receiving a read command from an external device, in response to the read command, performing, based on a reference voltage, a first cell counting operation with respect to the plurality of memory cells, adjusting at least one read voltage of first through nth read voltages (where n is a natural number greater than 1) based on a first result of the first cell counting operation, and performing, based on the adjusted at least one read voltage, a read operation corresponding to the read command with respect to the plurality of memory cells.