Reverse Reading Blocks for Floating Gate Coupling Compensation
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Solution Overview
Problem
In non-volatile memory systems, especially those using NAND flash memory, floating gate to floating gate coupling leads to shifts in apparent charge storage, causing erroneous readings due to electrical field interactions between adjacent memory cells, particularly as memory cells shrink and threshold voltage distributions become narrower, affecting multi-state devices more significantly.
Innovation Solution
Implementing reverse reading blocks where data is read in the opposite direction of programming, applying compensations based on charge stored in adjacent word lines to account for coupling effects, by starting the read operation from the last word line and ending with the first, and buffering data from adjacent word lines to maintain accurate readings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If memory cells are shrunk to increase storage density, then storage capacity is improved, but floating gate coupling effects worsen causing threshold voltage shifts and read errors
Solution Approach 1:
The patent applies reverse reading by reading word lines in the opposite order of programming (from last programmed word line to first). This inversion of the read sequence allows compensation for floating gate coupling effects, as the read operation accounts for charge shifts induced by subsequently programmed adjacent cells, thereby maintaining read accuracy despite cell shrinkage
Solution Approach 2:
The patent changes the reading sequence parameter from conventional (first to last word line) to reverse (last to first word line). This parameter change enables the system to compensate for coupling effects by reading adjacent word lines in an order that accounts for charge shifts, thereby maintaining threshold voltage measurement accuracy in scaled devices
2Ease of operation
If conventional reading order is used, then reading simplicity is maintained, but coupling-induced read errors increase
Solution Approach 1:
The patent inverts the conventional reading order to read from the last programmed word line to the first. This reverse reading approach maintains operational simplicity while improving measurement precision, as it naturally compensates for floating gate coupling effects that occur during subsequent programming operations
3Reliability
If reverse reading is implemented, then coupling compensation is improved, but operational complexity increases
Solution Approach 1:
The patent implements reverse reading by simply inverting the word line read sequence from conventional (0 to N-1) to reverse (N-1 to 0). This approach improves data retrieval accuracy through coupling compensation while minimizing operational complexity, as the inversion can be implemented through straightforward control logic changes without requiring complex additional circuitry
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 reduces errors in data retrieval by compensating for floating gate coupling, maintaining data integrity and reducing the number of sense operations required, thereby enhancing the performance and reliability of non-volatile memory systems.
Implementation Method 1
floating gate to floating gate coupling leads to shifts in apparent charge storage, causing erroneous readings due to electrical field interactions between adjacent memory cells
Data Source
AI summary
Shifts in the apparent charge stored by a charge storage region such as a floating gate in a non-volatile memory cell can occur because of electrical field coupling based on charge stored in adjacent (or other) charge storage regions. Although not exclusively, the effects are most pronounced in situations where adjacent memory cells are programmed after a selected memory cell. To account for the shift in apparent charge, one or more compensations are applied when reading storage elements of a selected word line based on the charge stored by storage elements of other word lines. Efficient compensation techniques are provided by reverse reading blocks (or portions thereof) of memory cells. By reading in the opposite direction of programming, the information needed to apply (or select the results of) an appropriate compensation when reading a selected cell is determined during the actual read operation for the adjacent word line rather than dedicating a read operation to determine the information.