Nonvolatile Memory Read Voltage Tracking via Segmented Distribution Assessment
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing nonvolatile memory systems, such as NAND flash memory, face challenges in accurately reading data due to variations in threshold voltage distributions caused by errors like data retention and read disturbance, leading to bit errors and increased stress on memory cells when using default read voltages, which can fail error correction processing and result in data errors.
Innovation Solution
A memory system that uses four voltage values to determine a read voltage by calculating intermediate voltages based on the distribution of memory cells across specific voltage ranges, reducing the number of read voltage applications and minimizing stress on memory cells by tracking the data read voltage without assessing the full threshold distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If default read voltage is used for reading data from nonvolatile memory, then the reading operation can be performed, but bit errors occur due to threshold voltage distribution variations and error correction processing fails
Solution Approach 1:
The patent segments the voltage tracking process into two distinct parts: (1) initial comprehensive threshold distribution assessment to establish baseline characteristics, and (2) subsequent simplified tracking using only read voltage applications without full distribution assessment. This segmentation allows the system to achieve reliable data reading by combining initial precision with ongoing efficiency, resolving the contradiction between reading reliability and measurement precision.
Solution Approach 2:
The patent applies preliminary action by performing a complete threshold distribution assessment before normal reading operations begin. This initial assessment establishes accurate baseline threshold voltage characteristics, enabling the system to subsequently use simplified tracking methods that apply read voltages without reassessing the full distribution. The preliminary action ensures that reliability is established upfront, allowing precision to be maintained through the simplified tracking approach.
2Reliability
If multiple read voltages are applied to track threshold distribution accurately, then reading accuracy improves, but the number of read operations increases causing increased stress on memory cells
Solution Approach 1:
The patent segments the voltage application process into an initial phase where comprehensive threshold distribution assessment is performed, and a subsequent phase where only necessary read voltages are applied for tracking. This segmentation reduces the total number of voltage applications by eliminating redundant full distribution assessments after the initial one, thereby maintaining error correction success while reducing stress on memory cells from excessive read operations.
Solution Approach 2:
The patent applies partial action by performing only the necessary read voltage applications for tracking threshold voltage shifts, rather than repeatedly assessing the full threshold distribution. This partial approach applies just enough voltage stress to maintain reading accuracy through successful error correction, while avoiding excessive stress from redundant comprehensive assessments, thus resolving the contradiction between reliability and harmful factors.
3Reliability
If comprehensive threshold distribution assessment is performed for each read operation, then reading accuracy is maintained, but reading speed decreases due to increased processing time
Solution Approach 1:
The patent segments the reading process into an initial comprehensive assessment phase and subsequent simplified tracking phases. During normal operations, the system performs only necessary read voltage applications without repeating full distribution assessments, thereby maintaining data integrity through continued tracking while significantly improving reading speed by eliminating time-consuming redundant assessments.
Solution Approach 2:
The patent applies preliminary action by completing the comprehensive threshold distribution assessment before normal reading operations begin. This upfront assessment establishes baseline characteristics that enable subsequent rapid tracking using simplified methods, thus maintaining data integrity through the preliminary work while achieving high reading speeds during normal operations without repeated comprehensive assessments.
Data Source
AI summary
According to an embodiment, a controller specifies a first voltage range that has a first distribution quantity, a second voltage range that is adjacent to a lower voltage side of the first voltage range, and a third voltage range that is adjacent to a higher voltage side of the first voltage range. The first distribution quantity is a minimum value of the memory cells. The controller determines a read voltage by using the first voltage range, a first representative voltage value in the first voltage range, the first distribution quantity, a second distribution quantity corresponding to the second voltage range, and a third distribution quantity corresponding to the third voltage range.