Low Margin Read with CRC Comparison for Soft Memory Cells
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Solution Overview
Problem
Non-volatile memory devices face reliability issues during read operations due to soft programmed memory cells, which can be misinterpreted as either a logical '0' or '1' due to threshold voltage being below the low margin threshold voltage, leading to unreliable data retrieval.
Innovation Solution
The implementation of a low margin read operation combined with a cyclic redundancy check (CRC) code comparison using specific reference voltages to identify and correct soft programmed memory cells, ensuring reliable data retrieval by distinguishing between logical '0' and '1' states through CRC code matching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a memory cell is weakly programmed (soft programmed), then programming time or energy is reduced, but the threshold voltage falls below the low margin threshold voltage causing unreliable read operations
Solution Approach 1:
The patent applies preliminary action by performing a low margin read operation immediately after programming to identify soft programmed memory cells before they cause read errors. The controller detects cells with threshold voltages below the low margin threshold voltage and marks them for repair, preventing unreliable reads while allowing weak programming to proceed
Solution Approach 2:
The patent implements feedback by using the results of low margin read operations to identify and repair soft programmed memory cells. The controller receives read data, compares it against expected values, and uses this feedback information to determine which cells require additional programming pulses, creating a closed-loop system that ensures data reliability
2Device complexity
If traditional read operations are used, then device complexity is low, but soft programmed memory cells cannot be reliably distinguished from erased cells
Solution Approach 1:
The patent applies segmentation by dividing the read operation into multiple stages: first performing a low margin read to identify potentially soft programmed cells, then performing additional reads on specific cell groups to determine their actual state. This segmented approach allows precise differentiation between soft programmed and erased cells without requiring complete system redesign
Solution Approach 2:
The patent uses partial action by applying additional programming pulses only to specific memory cells identified as soft programmed, rather than re-programming entire blocks. This targeted approach maintains measurement precision for individual cells while minimizing overall device complexity and operation time
Data Source
AI summary
A method for a low margin read operation that compares CRC codes receives known data and a CRC code generated from the known data. A CRC code is generated from data read from a memory cell at a first low margin reference voltage. The CRC code from the known data and the CRC code from the read data are compared and, if the codes do not match, a failed read operation is indicated. If the CRC codes do match, data is read from the memory cell at a second low margin reference voltage that is greater than the first low margin reference voltage. A CRC is generated from this read operation. If the two CRC codes match, the read operation is indicated as passed.