Multi-pass Memory Programming via Word Line Coupling
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Solution Overview
Problem
Programming accuracy in non-volatile memory devices, particularly in multi-level flash memory, is compromised due to capacitive coupling from neighboring storage elements, which can lead to inaccuracies in data storage and retrieval.
Innovation Solution
A multi-pass programming method is employed, where the first pass involves programming and verifying storage elements with a set of verify voltages, followed by a second pass with different verify voltages and pass voltages applied to adjacent elements or word lines, to compensate for capacitive coupling and improve programming accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single-pass programming process is used, then the programming speed is high, but the programming accuracy deteriorates due to capacitive coupling from neighboring storage elements
Solution Approach 1:
The programming process is divided into multiple passes, where each pass targets specific storage elements with different verify voltage criteria. This segmentation allows the system to address capacitive coupling effects by processing elements in staged groups rather than simultaneously, thereby improving programming accuracy without requiring complete process redesign
Solution Approach 2:
The first pass of programming establishes preliminary threshold voltage levels in storage elements before the second pass refines them. By performing preliminary programming actions first, the system creates a foundation that reduces the impact of capacitive coupling in subsequent refinement passes, improving overall accuracy
2Measurement precision
If verify voltages are applied to verify programming status, then programming accuracy is improved, but the threshold voltage distribution widens due to capacitive coupling effects
Solution Approach 1:
Different verify voltage levels are applied to different passes targeting specific storage elements. The first pass uses verify voltages optimized for initial programming, while the second pass uses different verify voltages optimized for refinement. This local differentiation of verify conditions allows accurate verification without uniformly widening the threshold voltage distribution across all elements
Solution Approach 2:
The programming and verification process is performed periodically in multiple passes rather than continuously in a single operation. This periodic approach allows the threshold voltage distribution to stabilize between passes, reducing cumulative capacitive coupling effects while maintaining verification accuracy
3Manufacturing precision
If multiple passes are used to improve programming accuracy, then the programming precision is improved, but the programming time increases
Solution Approach 1:
The second pass of programming targets only those storage elements that did not meet the verify criteria in the first pass, rather than re-programming all elements. This partial action approach refines programming precision for problematic elements without unnecessarily extending the total programming time for elements that were already correctly programmed
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach narrows the threshold voltage distribution, reducing interference effects and enhancing programming accuracy by effectively compensating for capacitive coupling, thereby improving data fidelity in multi-level flash memory devices.
Implementation Method 1
capacitive coupling from neighboring storage elements, which can lead to inaccuracies in data storage and retrieval
Data Source
Figure 1a~1b
Figure 1c
Figure 2~3
AI summary
A multiple pass programming scheme is optimized using capacitive coupling in the word line to word line direction during program-verify operations. A different pass voltage is used in different programming passes on an adjacent word line of a selected word line which is being verified. In particular, a lower pass voltage can be used in a first pass than in a second pass. The programming process may involve a word line look ahead or zigzag sequence in which WLn is programmed in a first pass, followed by WLn+ 1 in a first pass, followed by WLn in a second pass, followed by WLn+1 in a second pass. An initial programming pass may be performed before the first pass in which storage elements are programmed to an intermediate state and/or to a highest state.