Flash Memory Programming Method for Read Margin Compensation
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Solution Overview
Problem
Flash memory devices face challenges in maintaining adequate read margins between memory cell data states due to electric field and F-poly coupling effects, as well as hot temperature stress, which lead to expanded threshold voltage distributions and reduced data state discrimination.
Innovation Solution
A programming method for flash memory devices that involves a primary programming operation followed by a secondary programming operation, using verify and read voltages to detect and adjust threshold voltages of memory cells to ensure they are within specific regions, thereby increasing the read margin between data states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional programming methods are used, then programming time is reduced, but threshold voltage distributions expand due to coupling effects and temperature stress, reducing read margin
Solution Approach 1:
The patent applies preliminary action by performing a detection operation before the programming operation to identify memory cells with threshold voltages in problematic regions. This allows the system to pre-identify cells that need special handling, then during programming, selectively re-program only those detected cells to compensate for expected threshold voltage expansion due to coupling effects and temperature stress, thereby maintaining read margin without requiring complete re-programming of all cells
Solution Approach 2:
The patent implements feedback by incorporating a detection operation that measures actual threshold voltages of memory cells before programming. The detection results are fed back to the control logic, which then determines which cells need re-programming. This feedback mechanism allows dynamic adjustment of the programming process based on actual cell states, ensuring read margin is maintained while avoiding unnecessary programming operations on cells that are already within acceptable ranges
2Reliability
If threshold voltage distributions are tightly controlled, then read margin is improved, but programming time increases significantly
Solution Approach 1:
The patent applies partial action by selectively re-programming only the subset of memory cells that were detected to have threshold voltages in problematic regions, rather than re-programming all memory cells. This partial approach maintains data state discrimination for cells that need it while avoiding unnecessary programming time consumption on cells that are already within acceptable voltage ranges
Solution Approach 2:
By performing detection before programming to identify cells that will likely fall into problematic threshold voltage regions after programming, the system can prepare and target only those specific cells for re-programming. This preliminary identification avoids the need to scan and re-program the entire memory array, significantly reducing programming time while ensuring adequate read margin
3Manufacturing precision
If programming voltage increment is reduced, then threshold voltage control precision is improved, but programming time increases significantly
Solution Approach 1:
The detection operation performs preliminary measurement of threshold voltages before programming, allowing the system to predict which cells will end up in problematic voltage regions. This enables the use of larger programming voltage increments during the actual programming operation, since the system already knows which cells need precise control and can apply standard increment sizes to the rest, thereby maintaining precision where needed while improving overall programming speed
Data Source
AI summary
A programming method of a flash memory device having a plurality of memory cells for storing multi-bit data indicating one of a plurality of states. The programming method includes programming selected memory cells using multi-bit data to have one of the states; detecting programmed memory cells arranged within a predetermined region of threshold voltage distribution each corresponding to at least two of the states, wherein predetermined regions of the respective at least two states are selected by one of a first verify voltage and a read voltage and a second verify voltage, the first verify voltage being lower than the second verify voltage and higher than the read voltage; and simultaneously programming detected memory cells of the at least two states to have a threshold voltage being equivalent to or higher than the second verify voltage corresponding to each of the states.