Non-volatile Memory Coupling Compensation via Adjacent Cell State Sensing
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Solution Overview
Problem
The challenge in non-volatile semiconductor memory, particularly in multi-state flash memory devices, is the floating gate to floating gate coupling that leads to erroneous readings due to shifts in apparent charge storage, exacerbated by shrinking memory cell sizes and increased coupling effects, which affects the precision of threshold voltage ranges and programming states.
Innovation Solution
The proposed solution involves programming non-volatile storage elements through a method that includes coarse and fine verification levels to mitigate coupling effects, using a managing circuit to control programming processes and sense modules to adjust programming voltages, ensuring accurate data storage and retrieval by compensating for neighboring memory cell states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If memory cell size is reduced to increase storage density, then storage capacity is improved, but coupling effects between adjacent floating gates increase causing threshold voltage shifts and read errors
Solution Approach 1:
The patent applies preliminary action by performing a read operation on the neighboring memory cell before reading the target memory cell. This preliminary read captures the state of the neighboring floating gate before it can couple with and distort the target cell's threshold voltage during the subsequent read operation, thereby compensating for coupling effects and maintaining read accuracy despite reduced cell spacing
Solution Approach 2:
The patent implements feedback by using the read result from the neighboring memory cell to adjust or compensate for coupling effects on the target memory cell's read operation. The system feeds back information about the neighboring cell's charge state to correct threshold voltage shifts in the target cell, ensuring accurate data retrieval even when cells are densely packed
2Quantity of substance
If multiple programming states are used to increase data capacity, then storage capacity is improved, but the precision of threshold voltage ranges decreases due to coupling effects
Solution Approach 1:
The patent applies preliminary action by reading the neighboring cell's state before performing the target cell read operation. This preliminary information allows the system to anticipate and compensate for coupling-induced threshold voltage shifts, maintaining precise distinction between multiple programming states even when coupling effects are present
Solution Approach 2:
The patent uses feedback mechanisms where the neighboring cell's read result is fed back to adjust the interpretation of the target cell's threshold voltage. This feedback loop enables the system to maintain accurate state identification in multi-state memory despite coupling effects that would otherwise blur the boundaries between programming states
3Adaptability or versatility
If adjacent memory cells are programmed at different times, then programming flexibility is improved, but coupling effects cause apparent charge shifts and erroneous readings
Solution Approach 1:
The patent applies preliminary action by performing a read operation on the neighboring cell that was programmed at a different time before reading the target cell. This preliminary read captures the actual charge state of the neighboring cell, allowing the system to compensate for its coupling effect on the target cell's threshold voltage measurement, thereby restoring measurement accuracy while preserving programming flexibility
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 effectively reduces the impact of floating gate coupling, enhancing the accuracy of data storage and retrieval in multi-state flash memory devices by maintaining precise threshold voltage distributions and preventing memory cells from being locked out or misread.
Implementation Method 1
Electrons from the channel are injected into the floating gate. When electrons accumulate in the floating gate, the floating gate becomes negatively charged and the threshold voltage of the memory cell is raised
Implementation Method 2
Both EEPROM and flash memory utilize a floating gate that is positioned above and insulated from a channel region in a semiconductor substrate. The threshold voltage of the transistor is controlled by the amount of charge that is retained on the floating gate
Implementation Method 3
Shifts in the apparent charge stored on a floating gate can occur because of the coupling of an electric field based on the charge stored in adjacent floating gates
Data Source
AI summary
Shifts in the apparent charge stored on a floating gate (or other charge storing element) of a non-volatile memory cell can occur because of the coupling of an electric field based on the charge stored in adjacent floating gates (or other adjacent charge storing elements). To compensate for this coupling, the read or programming process for a given memory cell can take into account the programmed state of an adjacent memory cell. To determine whether compensation is needed, a process can be performed that includes sensing information about the programmed state of an adjacent memory cell (e.g., on an adjacent bit line or other location).