Fast Look Neighbor Ahead for Memory Cell Read
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Solution Overview
Problem
The shrinking size of memory circuitry in non-volatile semiconductor memory devices leads to increased neighbor word line interference (NWI), which complicates the programming and data retention of memory cells, causing a widening of threshold voltage (Vth) distribution and reduced programming efficiency.
Innovation Solution
A storage device with a non-volatile memory system that includes a controller configured to determine data states for adjacent memory cells, identify zones based on these states, and apply specific bit line clamping voltages to mitigate NWI effects during read operations, using a look neighbor ahead (LNA) method to classify data state combinations into zones corresponding to unique bit line clamping voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If memory circuitry size is shrunk to increase storage density, then storage capacity is improved, but neighbor word line interference increases causing threshold voltage distribution to widen
Solution Approach 1:
The patent performs preliminary determination of data states for first and second neighboring word lines before reading the selected word line. This advance knowledge allows the system to identify zones based on neighbor states and select appropriate bit line clamping voltages, thereby compensating for NWI effects before they degrade the read operation. The preliminary action of reading neighbor word lines and determining their data states enables proactive mitigation of interference on the target word line.
Solution Approach 2:
The patent applies different bit line clamping voltages to different zones of memory cells based on their specific neighbor word line data state combinations. Instead of using a uniform approach, the system divides memory cells into multiple zones where each zone receives a tailored clamping voltage selected from a set of voltages. This localized differentiation allows precise compensation for NWI effects that vary across different spatial regions and data state combinations, thereby tightening the overall threshold voltage distribution.
2Speed
If conventional read operations are performed without considering neighbor word line states, then operation speed is maintained, but data read accuracy deteriorates due to NWI
Solution Approach 1:
The system performs preliminary determination of neighbor word line data states before executing the actual read operation on the selected word line. This preliminary action includes reading first and second neighboring word lines, determining their data states, and identifying zones based on these states. By preparing the appropriate bit line clamping voltage in advance based on neighbor states, the system ensures accurate reading of the target word line without sacrificing operational speed, as the compensation parameters are ready before the critical read operation.
Solution Approach 2:
The patent incorporates feedback from neighbor word line data states into the read operation control. The system determines data states of first and second neighboring word lines, uses this feedback information to identify zones, and then selects appropriate bit line clamping voltages based on the identified zones. This feedback mechanism allows the read operation to adapt to actual neighbor states, thereby maintaining high data read accuracy while preserving operation speed through efficient voltage selection.
Data Source
AI summary
A storage device is disclosed. The storage device is configured to: determine data states for a first set of memory cells of a first neighboring word line of the and a second set of memory cells of a second neighboring word line, the first and the second neighboring word lines being adjacent to a selected word line; identify a zone of a plurality of zones for each data state combination of the data states, each data state combination comprising a data state of a memory cell of the first set of memory cells and a data state of a memory cell of the second set of memory cells, each zone of the plurality of zones corresponding to a bit line clamping voltage; and perform a read operation on the selected word line including applying each bit line clamping voltage corresponding to any zones identified.