Memory System Voltage Correction for Over-Programming
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Solution Overview
Problem
Existing memory systems face challenges in accurately reading data due to unintended shifts in threshold voltage distributions across memory cells, leading to errors in data retrieval, particularly due to over-programming and read disturbances, which affect the reliability and performance of NAND flash memory devices.
Innovation Solution
A memory system with a voltage correction circuit that dynamically adjusts the initial program voltage and step-up voltage based on real-time detection of threshold voltage shifts during write operations, using a voltage information table to optimize voltage settings and minimize errors by correcting voltage values based on the number of memory cells shifted to incorrect states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed initial program voltage and step-up voltage are used for write operations, then the write operation process is simple, but threshold voltage shifts cause over-programming errors and data reading errors
Solution Approach 1:
The patent implements a feedback mechanism where the memory controller detects threshold voltage shifts of memory cells during read operations, uses this detection result to determine corrected voltage values, and applies these corrected voltages in subsequent write operations. This closed-loop feedback system dynamically adjusts voltage parameters to compensate for threshold voltage shifts, thereby reducing over-programming errors and improving data reading accuracy without requiring complex hardware modifications.
2Reliability
If voltage correction based on threshold voltage detection is implemented, then over-programming errors are reduced, but the write operation time increases due to additional detection and correction steps
Solution Approach 1:
The patent performs threshold voltage detection and voltage correction in advance during idle periods or between write operations. The memory controller detects threshold voltage shifts and determines corrected voltage values before actual write operations are needed. This preliminary action allows the system to have corrected voltage parameters ready, so that during actual write operations, only the simplified voltage application step remains, minimizing the time penalty while maintaining high write accuracy.
3Adaptability or versatility
If standard program voltage is used for all memory cells, then the voltage control is simple, but memory cells with shifted threshold voltages cannot be properly programmed
Solution Approach 1:
The patent applies local quality by determining different corrected voltage values for different memory cells or memory cell groups based on their individual threshold voltage shift characteristics. Instead of using a uniform voltage correction for all cells, the memory controller detects and compensates for threshold voltage shifts on a per-cell or per-group basis, allowing each memory cell to receive the appropriate voltage level tailored to its specific characteristics, thereby improving programming accuracy while managing complexity through selective adaptation.
Data Source
AI summary
According to one embodiment, a memory system includes a semiconductor memory having a plurality of memory cells and a memory controller that controls the semiconductor memory to perform write and read operations and a read operation. The memory controller causes the semiconductor memory to execute a first write operation using a first voltage, detects, in a read operation, first memory cells among the plurality of memory cells that have a threshold voltage higher than a voltage value corresponding to data to be stored and sets a second voltage used for a second write operation after the first write operation based on a detection result of the first memory cells.