Dynamic Read Voltage Control for Non-Volatile Memory Error Reduction
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Solution Overview
Problem
Non-volatile memory cells experience charge loss and charge transfer over time, leading to a widening of threshold voltage distribution, which can result in errors during read operations in memory devices.
Innovation Solution
A memory system and method that dynamically determines a read voltage level based on the mean difference and standard deviation ratio of threshold voltage distributions, adjusting the voltage to accurately read data from non-volatile memory cells by shifting or modifying the read voltage level to minimize errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed read voltage is used for read operations, then the device structure is simple and operation is easy, but read errors increase over time due to threshold voltage distribution widening
Solution Approach 1:
The patent implements dynamic read voltage adjustment by determining optimal read voltages based on threshold voltage distribution characteristics (mean and standard deviation) obtained during manufacturing or operation. The read voltage is no longer fixed but dynamically adapted to the actual threshold voltage distribution of the memory cells, resolving the contradiction between simple operation and read accuracy over time.
Solution Approach 2:
The patent changes the read voltage parameter based on the threshold voltage distribution parameters (mean and standard deviation). By calculating optimal read voltages as a function of these distribution parameters, the system adapts to threshold voltage shifts and widening that occur over time, maintaining high read accuracy without requiring complex real-time monitoring during read operations.
2Measurement precision
If the read voltage level is adjusted to compensate for threshold voltage distribution changes, then read accuracy is improved, but the voltage control mechanism becomes more complex
Solution Approach 1:
The patent performs preliminary determination of optimal read voltages based on threshold voltage distribution characteristics. The mean and standard deviation of the threshold voltage distribution are obtained in advance (during manufacturing or initial operation), and optimal read voltages are calculated beforehand. This preliminary action eliminates the need for complex real-time voltage adjustment mechanisms during read operations, achieving high accuracy without operational complexity.
Solution Approach 2:
The patent uses threshold voltage distribution parameters (mean and standard deviation) as feedback to determine optimal read voltages. By monitoring how the threshold voltage distribution changes over time and using this information to adjust read voltages, the system maintains accurate data recognition. The feedback mechanism is simplified by using only two key parameters (mean and standard deviation) rather than full distribution analysis.
3Reliability
If the read voltage is adapted to threshold voltage distribution changes, then read errors are reduced, but additional measurements and calculations are required
Solution Approach 1:
The patent extracts only the essential parameters from the threshold voltage distribution - specifically the mean and standard deviation. Rather than analyzing the complete threshold voltage distribution or performing complex measurements, the invention isolates these two key parameters that sufficiently characterize the distribution. This extraction simplifies the measurement and calculation requirements while maintaining the ability to determine optimal read voltages for high read reliability.
Data Source
AI summary
A memory system determines a level of a read voltage, which is used for reading or recognizing data stored in non-volatile memory cells, in response to a change of a threshold voltage distribution which gradually widens due to charge loss or charge transfer in the non-volatile memory cells over time, so that it is possible to provide an apparatus and method which can avoid or reduce an error in a read operation.