Memory Programming Process Compensates for Neighbor Word Line Interference
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Solution Overview
Problem
In semiconductor memory devices, neighbor word line interference (NWI) causes threshold voltage upshifts in memory cells, leading to data retention issues and read errors, especially as device dimensions shrink and the distance between word lines decreases.
Innovation Solution
Generating compensation data based on the assigned data states of adjacent memory cells to adjust programming parameters, such as bit line voltage, word line voltage, and sense node discharge duration, to mitigate the effects of NWI during programming operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If device dimensions are shrunk and distance between word lines is decreased, then memory density is improved, but neighbor word line interference increases causing threshold voltage upshifts and data retention issues
Solution Approach 1:
The patent applies preliminary action by determining the data states of adjacent memory cells before programming the target memory cell. This advance knowledge allows the programming operation to pre-compensate for the threshold voltage upshift that will be caused by the adjacent cell's programming, thereby preventing the interference effect rather than correcting it after occurrence
Solution Approach 2:
The patent implements parameter changes by dynamically adjusting programming parameters (such as programming voltage level, pulse width, or number of programming pulses) based on the determined data state of the adjacent memory cell. When the adjacent cell is in a high data state, the programming parameters for the target cell are modified to compensate for the expected interference, thus maintaining reliable programming despite reduced word line spacing
2Reliability
If programming parameters are adjusted to compensate for adjacent cell interference, then data retention is improved, but programming operation complexity increases
Solution Approach 1:
The patent applies local quality by implementing compensation only for specific memory cells that are adjacent to cells in high data states. The programming operation selectively adjusts parameters based on the local condition of each target cell's neighbors, rather than applying uniform compensation to all cells. This targeted approach improves data retention for affected cells while minimizing the overall increase in programming complexity
Data Source
AI summary
Techniques are provided to compensate for neighbor word line interference when programming memory cells connected to a selected word line WLn. Before programming, the assigned data states of WLn and WLn+1 are compared and corresponding compensation data is generated. The compensation data may be stored in latches of sense circuits to modify the verify tests which occur during programming. The compensation can involve adjusting the bit line voltage, word line voltage, sense node discharge period and/or trip voltage. During a verify test, the compensation data can cause a WLn memory cell to complete programming when its threshold voltage is lower than would be the case with no compensation. When the WLn+1 memory cells are subsequently programmed, an upshift in the threshold voltage of the WLn memory cell offsets the compensation.