Non-volatile Memory Read Method Using Conditional Soft Decision Voltages
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Solution Overview
Problem
Flash memory devices face increased error rates and reliability issues as the number of bits programmed in each memory cell increases, due to overlapping threshold voltage distributions, leading to read failures and data corruption.
Innovation Solution
Implementing a method that uses both hard decision and soft decision voltages for reading memory cells, allowing for error correction by determining if errors are correctable with initial hard decision results, and if not, employing additional soft decision read operations to improve accuracy, thereby reducing performance loss and overhead in error correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multi-bit data is programmed in each memory cell to increase storage capacity, then integration density is improved, but read reliability deteriorates due to overlapping threshold voltage distributions
Solution Approach 1:
The patent segments the read operation into multiple stages: first a hard decision read to obtain initial data, then conditional soft decision reads to correct errors. This segmentation allows the system to handle high-capacity multi-bit cells while maintaining reliability by applying different read strategies to different data portions.
Solution Approach 2:
The patent changes the voltage parameter dynamically during the read process. It uses hard decision voltages for initial reading, then switches to soft decision voltages for error correction when needed. This parameter change enables the system to adapt to the degraded signal quality caused by multi-bit programming.
2Reliability
If soft decision read operations are performed to correct errors in multi-bit cells, then read reliability is improved, but performance loss increases due to additional read operations
Solution Approach 1:
The patent applies partial action by performing soft decision reads only partially - specifically, only when errors are detected in the hard decision read results. The controller conditionally executes soft decision reads based on error detection, avoiding unnecessary additional read operations for error-free data and thus minimizing performance loss.
Solution Approach 2:
The patent implements feedback control where the controller monitors the results of hard decision reads, detects errors, and then decides whether to initiate soft decision read operations. This feedback mechanism ensures that performance-critical paths are not unnecessarily delayed while still providing error correction when needed.
3Reliability
If error correction operations are performed on all read data, then data reliability is improved, but overhead increases due to processing all data through correction
Solution Approach 1:
The patent applies partial action by performing error correction only on data that actually contains errors. The controller detects errors in hard decision read results and then selectively applies soft decision reads and correction operations only to the affected data portions, rather than processing all read data through the full correction pipeline.
Data Source
AI summary
In one embodiment, the method for reading memory cells in an array of non-volatile memory cells includes reading data from a memory cell using a set of hard decision voltages and at least a first set of soft decision voltages based on a single read command.