Flash Memory Capacitive Coupling Compensation
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Solution Overview
Problem
The increasing performance demands in electronic systems require improved speed and memory density in flash memory devices, but the reduction in size of NAND flash memory devices leads to floating gate-to-floating gate capacitive coupling, affecting the verification, reading, and erasing of adjacent cells.
Innovation Solution
A method is introduced to address capacitive coupling by programming a target cell and adjacent cells to specific threshold voltages, measuring the voltage difference, and performing a soft programming operation if the difference exceeds a predetermined threshold to ensure uniform threshold voltages across the memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the size of NAND flash memory device is decreased to improve memory density and performance, then memory density increases, but floating gate-to-floating gate capacitive coupling increases affecting verification, reading, and erasing operations
Solution Approach 1:
The patent applies preliminary anti-action by performing a soft programming operation on the first cell before normal programming to pre-compensate for the capacitive coupling effect. This preliminary action adjusts the threshold voltage of the first cell in advance, counteracting the expected voltage increase caused by adjacent cell programming, thereby eliminating the need for re-verification or correction after the main programming operation.
Solution Approach 2:
The patent changes the threshold voltage parameter of the first cell dynamically based on the programming state of adjacent cells. By measuring the threshold voltage of the first cell before and after adjacent cell programming, and applying a soft programming operation when the voltage difference exceeds a predetermined threshold, the system adapts the threshold voltage parameter to compensate for capacitive coupling effects, ensuring accurate data storage and retrieval.
2Productivity
If adjacent cells are programmed to increase memory capacity utilization, then storage efficiency improves, but threshold voltage of target cell changes due to capacitive coupling affecting operation reliability
Solution Approach 1:
The patent implements feedback by measuring the threshold voltage of the first cell before and after programming adjacent cells, comparing the voltage difference against a predetermined threshold, and conditionally applying a soft programming operation. This feedback mechanism ensures that capacitive coupling effects are detected and corrected, maintaining operation reliability while allowing efficient utilization of adjacent cells for storage.
Solution Approach 2:
The patent dynamically adjusts the threshold voltage parameter of the first cell based on the programming state of adjacent cells. When the threshold voltage difference caused by capacitive coupling exceeds a predetermined threshold, a soft programming operation is applied to compensate, thereby maintaining reliable operation despite high storage efficiency utilization through adjacent cell programming.
3Reliability
If soft programming operation is performed to compensate threshold voltage changes, then operation reliability improves, but additional programming time is required
Solution Approach 1:
The patent applies partial action by performing a soft programming operation only when necessary - specifically, when the threshold voltage difference caused by capacitive coupling exceeds a predetermined threshold. This conditional approach avoids unnecessary soft programming operations on cells that are not affected by capacitive coupling, thereby maintaining operation reliability while minimizing additional programming time overhead.
Solution Approach 2:
The patent performs the soft programming operation as a preliminary step before normal programming when the threshold voltage difference is detected to be significant. By addressing the capacitive coupling effect in advance, the system prevents potential read/verify failures rather than requiring corrective actions after the main programming operation, thus improving reliability without adding significant time overhead.
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 achieves a tighter threshold voltage distribution, enhancing the reliability and efficiency of memory operations by minimizing the impact of capacitive coupling, thereby improving the performance and consistency of memory operations.
Implementation Method 1
floating gate-to-floating gate coupling that occurs as the memory cells get closer together. For example, one cell's threshold voltage can be increased by increasing the threshold voltage of adjacent cells. The increased capacitive coupling between the floating gates can affect the verification, reading, and erasing of adjacent cells.
Data Source
AI summary
A method for erasing a non-volatile memory device performs a block erase operation. The cells are then soft programmed and erase verified to determine if the threshold voltages indicate erased cells. A target cell is programmed to a first threshold voltage and verified. Adjacent cells are programmed and verified. The parasitic capacitance between the target cells and the adjacent cells causes the threshold voltage of the target cell to increase to a new threshold voltage with the programming of the adjacent cells. A difference between the new threshold voltage and the first threshold voltage is determined. If the difference is greater than or equal to a predetermined threshold, the target cell is soft programmed until the difference is less than the predetermined threshold.