Flash Memory High Voltage Circuit Leakage Control
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Solution Overview
Problem
NAND flash memory devices face challenges in accurately controlling program voltage during incremental step pulse programming, leading to undesired threshold voltages and incorrect programming due to minor fluctuations in voltage magnitude, especially in multi-level cells with small read margins.
Innovation Solution
A high voltage generating circuit comprising a charge pump, voltage dividing circuit, discharging circuit, comparing circuit, and controlling circuit is used to cut off the discharge path and deactivate the pumping clock signal during program verification periods, preventing leakage current and stabilizing the program voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the high voltage generating circuit remains active during program verification periods, then the voltage can be quickly applied when needed, but leakage current occurs and voltage magnitude becomes unstable
Solution Approach 1:
The discharge path is cut off in advance during program verification periods before the high voltage is actually needed. This preliminary action prevents leakage current and voltage instability while maintaining the capability to quickly apply voltage when the programming operation begins, as the circuit is already prepared and merely needs to reactivate the discharge path control.
2Productivity
If the discharge path is continuously maintained, then the high voltage generating circuit can respond quickly to programming needs, but leakage current drains power and reduces efficiency
Solution Approach 1:
The discharge path is controlled periodically - activated during program periods when high voltage is needed and cut off during program verification periods when it is not needed. This periodic control eliminates unnecessary power consumption during verification while maintaining quick response capability during actual programming operations, thereby improving overall efficiency without continuous energy loss.
3Adaptability or versatility
If the program voltage magnitude fluctuates, then the programming operation can be flexible and adaptive, but incorrect programming occurs due to undesired threshold voltages
Solution Approach 1:
The controller monitors and controls the discharge path based on the programming operation state. During program verification periods, the controller cuts off the discharge path to prevent voltage fluctuations that would cause incorrect programming. This feedback control mechanism maintains voltage precision during critical verification phases while allowing flexibility during active programming periods when the discharge path is controlled but not cut off.
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 solution prevents leakage current and overshooting, ensuring a stable program voltage magnitude, thereby improving the accuracy and reliability of programming in NAND flash memory devices.
Implementation Method 1
a charge pump adapted to generate a high voltage in response to a pumping clock signal
Implementation Method 2
a voltage dividing circuit adapted to divide the high voltage to produce a divided voltage result
Implementation Method 3
The discharging circuit is adapted to activate a discharge path located between the voltage dividing circuit and ground
Data Source
AI summary
A flash memory device is disclosed and includes; a memory cell array, a high voltage generating circuit generating a high voltage applied to a selected word line to select one or more memory cells in the memory cell array, and a controller. The controller cuts off a discharge path between the high voltage generating circuit and ground during a first period wherein the high voltage is not applied to a word line. The controller also deactivates the high voltage generating circuit during this first period.