Reverse Reading Blocks for Non-Volatile Memory Coupling Compensation
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Solution Overview
Problem
In non-volatile memory systems, particularly in NAND flash memory, the floating gate to floating gate coupling phenomenon leads to shifts in apparent charge stored on memory cells, causing erroneous readings due to electrical field coupling from adjacent cells, especially 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 the shifts in apparent charge, thereby determining appropriate compensation during the read operation to accurately read selected cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If memory cells are shrunk to increase storage capacity, then storage density is improved, but floating gate coupling errors increase causing reading accuracy to deteriorate
Solution Approach 1:
The patent inverts the conventional read sequence by reading word lines in reverse order (from last programmed to first programmed) instead of following the programming sequence. This inversion allows the read operation to benefit from compensation information that becomes available during the read process itself, thereby improving reading accuracy in shrunk memory cells where coupling errors are more significant.
Solution Approach 2:
The patent implements a feedback mechanism where the read operation of adjacent word lines provides compensation information that is used to correct reading errors in the current word line. The compensation value derived from previously read word lines is fed back to adjust the read threshold voltage, improving measurement precision despite the harmful coupling effects in scaled-down cells.
2Measurement precision
If reverse reading with compensation is implemented, then reading accuracy is improved, but device complexity increases
Solution Approach 1:
The patent employs a self-service approach where the read operation itself generates the compensation information needed for error correction. By reading adjacent word lines in sequence and using their charge states to determine compensation values, the system uses its own operational data to correct errors, avoiding the need for external compensation circuits or additional hardware complexity.
Solution Approach 2:
The patent merges the read operation with the compensation process into a single integrated sequence. Instead of performing separate read and compensation operations, the compensation information is obtained during the read process itself by sequentially reading adjacent word lines, thereby improving accuracy without adding separate compensation circuitry or increasing overall device complexity.
3Measurement precision
If reverse reading sequence is used, then compensation efficiency is improved, but operation time increases
Solution Approach 1:
The patent maintains continuity of useful action by performing the read operation in a continuous sequence without interrupting to perform separate compensation measurements. The reverse reading sequence allows each word line to be read immediately after its adjacent word line, keeping the compensation process continuous and integrated into the main read operation, thereby minimizing additional time overhead.
Solution Approach 2:
The patent applies preliminary action by pre-establishing the reverse reading sequence and compensation values before actual data retrieval is needed. The compensation information from adjacent word lines is obtained in advance during the sequential read process, allowing for faster correction during the main read operation and reducing overall time loss compared to post-read compensation methods.
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 the impact of floating gate coupling errors by efficiently compensating for charge shifts, ensuring accurate data retrieval and maintaining the integrity of multi-state memory cell states, thereby improving the reliability of non-volatile memory systems.
Implementation Method 1
the floating gate to floating gate coupling phenomenon leads to shifts in apparent charge stored on memory cells, causing erroneous readings due to electrical field coupling from adjacent 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.