Flash Memory Read Control Using Adaptive Soft Read Voltages
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Solution Overview
Problem
Non-volatile flash memory devices face challenges in accurately reading data due to overlapping threshold voltage distributions, which lead to increased read failure rates and reliability issues as the number of bits programmed in each memory cell increases.
Innovation Solution
A controller that performs a first soft read operation using specific soft read voltages and an error correction code (ECC) codec for soft decision decoding, followed by a second soft read operation with different voltages if the initial decoding fails, to improve data reading accuracy and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If multiple bits are programmed in each memory cell to increase storage capacity, then data storage capacity is improved, but read reliability deteriorates due to overlapping threshold voltage distributions
Solution Approach 1:
The read operation is segmented into multiple stages: first soft read operation with initial soft read voltages, followed by second soft read operation with additional soft read voltages if ECC decoding fails. This segmentation allows the system to progressively refine voltage selections to resolve overlapping threshold voltage distributions while maintaining high storage capacity
Solution Approach 2:
The patent implements dynamic voltage selection where additional soft read voltages are applied based on the results of the first soft read operation and ECC decoding performance. The voltage selection adapts dynamically to the actual threshold voltage distribution state, improving read reliability without sacrificing storage capacity
2Reliability
If additional soft read voltages are applied to improve read accuracy, then read reliability is improved, but operation time increases
Solution Approach 1:
The patent applies additional soft read voltages only partially - specifically when the first soft read operation followed by ECC decoding fails to correctly read data. This conditional application of excessive action (additional voltage operations) balances read accuracy improvement with operation time minimization
Solution Approach 2:
The system uses feedback from the ECC decoding result to determine whether to perform the second soft read operation. If the first soft read and ECC decoding succeed, no additional operations are performed. If they fail, the feedback triggers the second soft read with additional voltages, optimizing the trade-off between accuracy and time
Data Source
AI summary
The controller that controls a memory device includes: a processor suitable for controlling the memory device to perform a first soft read operation by using first soft read voltages; and an error correction code (ECC) codec suitable for performing a first soft decision decoding operation based on first soft read data obtained through the first soft read operation, wherein the processor controls the memory device to perform a second soft read operation with an additional read voltage, of second soft read voltages, that is different than any of the first soft read voltages and which is determined based on the first soft read data, according to whether the first soft decision decoding operation failed, and wherein the ECC codec performs a second soft decision decoding operation based on the first soft read data and second soft read data obtained through the second soft read operation.