Multi-Level Cell Flash Memory Read Method
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Solution Overview
Problem
Flash memory devices face reliability issues due to variations in threshold voltages of memory cells, leading to errors in read data, especially when threshold voltage distributions overlap, affecting the accuracy of read operations.
Innovation Solution
A method involving multiple read operations with varying voltages is employed, including hard decision and soft decision read operations, where soft decision data is generated through logical operations on results from different voltage applications, and error correction is performed using both hard and soft decision data to improve reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple read operations with varying voltages are performed to improve read accuracy, then reliability of read operations is improved, but operation time and complexity increase
Solution Approach 1:
The read operation is divided into multiple stages: first hard decision read operation, second hard decision read operation, and soft decision read operation. Each stage uses different voltage levels and processing methods to progressively improve read accuracy while managing time consumption through hierarchical error correction
Solution Approach 2:
The first hard decision read operation is performed preliminarily to obtain initial read data before performing the second hard decision read operation. This preliminary action allows the system to prepare correction data in advance, reducing the overall time penalty of multiple read operations
2Reliability
If multiple read operations with varying voltages are performed to improve read accuracy, then reliability of read operations is improved, but device complexity increases
Solution Approach 1:
The system uses feedback from the first hard decision read operation to perform correction on the second hard decision read operation. The correction data generated from comparing results at different voltage levels is fed back into the error correction process, creating a closed-loop system that improves reliability while managing complexity through systematic feedback mechanisms
3Measurement precision
If threshold voltage variations are corrected using multiple read operations, then measurement precision is improved, but operation complexity increases
Solution Approach 1:
The system changes the voltage parameter across multiple read operations to compensate for threshold voltage variations. By performing reads at different voltage levels (first voltage, second voltage, and soft decision voltage) and comparing results, the system achieves higher measurement precision while managing complexity through systematic parameter variation and error correction
Data Source
AI summary
According to an example embodiment of inventive concepts, an operating method of a non-volatile memory device includes: performing a first hard decision read operation that includes applying a first voltage if a selected word line of the non-volatile memory device; storing a result of the first hard decision read operation at a first latch of a page buffer in the non-volatile memory device; performing a second hard decision read operation that includes applying a second voltage to the selected word line, the second voltage being higher than the first voltage; and generating a first soft decision value using a result of the first hard decision read operation stored at the first latch.