Flash Memory Program Recovery Voltage Control
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Solution Overview
Problem
NAND-type flash memory devices face challenges in maintaining threshold voltage distribution characteristics due to the electron leakage phenomenon, known as the under tail phenomenon, which occurs during the program recovery operation, leading to deterioration of program distribution characteristics.
Innovation Solution
The method involves applying a first voltage to a selected word line and a second, lower voltage to non-selected word lines during programming, and then lowering the first voltage to a third voltage before recovering to a fourth voltage, which is typically ground voltage, ensuring simultaneous voltage recovery for both selected and non-selected word lines to prevent electron leakage and under tail phenomena.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high voltage is applied to the selected word line during program recovery operation, then programming speed is improved, but electron leakage occurs causing deterioration of threshold voltage distribution characteristics
Solution Approach 1:
The word lines are segmented into selected word lines and non-selected word lines, allowing different voltage levels to be applied to each group. The selected word line receives the first voltage (higher) while non-selected word lines receive the second voltage (lower), preventing electron leakage from non-selected lines while maintaining programming speed of selected lines.
Solution Approach 2:
Different voltage levels are applied locally to different word lines based on their selection status. The selected word line gets the higher programming voltage for fast programming, while non-selected word lines get the lower pass voltage to prevent unwanted electron leakage and maintain their threshold voltage characteristics.
2Reliability
If the first voltage is lowered to the third voltage before recovering to fourth voltage, then electron leakage is prevented, but programming time is increased
Solution Approach 1:
The method applies the first voltage to the selected word line before recovering it to the third voltage, performing the programming action in advance while the voltage is high. This allows programming to occur during the high-voltage phase, then the voltage is recovered to prevent leakage during the transition, minimizing the time penalty.
Solution Approach 2:
The voltage recovery process uses periodic action by first lowering the voltage from the first level to the third level, then recovering it to the fourth level. This staged voltage recovery prevents electron leakage during the transition while maintaining programming speed during the high-voltage phase.
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 prevents or reduces the under tail phenomenon, maintaining the integrity of threshold voltage distribution characteristics in NAND-type flash memory devices by preventing electron transfer during the program recovery operation.
Implementation Method 1
programming memory cells connected to a selected word line by applying a first voltage to the selected word line and a second voltage to non-selected word lines
Implementation Method 2
prevents or reduces the under tail phenomenon, maintaining the integrity of threshold voltage distribution characteristics in NAND-type flash memory devices by preventing electron transfer during the program recovery operation
Data Source
AI summary
A method of programming a flash memory includes programming memory cells connected to a selected word line by applying a first voltage to the selected word line and a second voltage to non-selected word lines, the second voltage being lower than the first voltage, lowering the first voltage of the selected word line to a third voltage after programming the memory cells connected to the selected word line, the third voltage being lower than the first voltage, and recovering a fourth voltage of the selected word line and the non-selected word lines, the fourth voltage being lower than the second and third voltages.