Flash Memory Word Line Recovery Voltage Control
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Solution Overview
Problem
As the number of memory cells connected to one word line increases in flash memory, the program voltage rising time also increases due to resistance-capacitance (RC) loading, leading to longer times for memory cells farther from the program voltage generator to reach the target voltage, which can result in threshold voltage distortion.
Innovation Solution
A flash memory system that includes a target voltage generator and a word line voltage controller to adjust the word line recovery voltage based on recovery control signals, reducing the program voltage rising time by controlling the target voltage level during the program execution operation period, and providing different voltages and supply times to adjacent and unselected word lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of memory cells connected to one word line increases, then the storage capacity is improved, but the program voltage rising time increases due to increased RC loading
Solution Approach 1:
The patent applies preliminary action by performing a word line recovery operation before the next program execution. During this recovery operation, a recovery voltage is applied to the word line to pre-charge the capacitive loading, so that when the program voltage is subsequently applied, the voltage rising time is reduced because the RC circuit already has some charge stored. This preparatory charging action addresses the time delay caused by high RC loading in high-density memory configurations.
2Quantity of substance
If the number of memory cells connected to one word line increases, then the storage capacity is improved, but threshold voltage distortion occurs in memory cells farther from the program voltage generator
Solution Approach 1:
The recovery voltage application performs a preliminary action that equalizes the potential distribution across the word line before program operation. By pre-charging the word line capacitance, the voltage drop across the word line resistance during program operation is reduced, ensuring that memory cells at different positions along the word line experience more uniform voltage levels, thereby reducing threshold voltage distortion.
Solution Approach 2:
The patent changes the voltage parameter by applying a specific recovery voltage level during the word line recovery operation. This recovery voltage is carefully selected to optimize the charge distribution on the word line, compensating for the resistive voltage drop that would otherwise cause threshold voltage distortion in distant memory cells. The parameter change in voltage level directly addresses the uniformity issue.
Data Source
AI summary
The present disclosure provides methods and apparatuses for reducing a program voltage rising time. In some embodiments, a flash memory includes a memory cell array including a plurality of memory cells, a target voltage generator configured to adjust a target voltage level of a word line recovery voltage provided to the plurality of memory cells, and a word line voltage controller configured to provide recovery control signals for controlling the target voltage level of the word line recovery voltage. The target voltage generator is further configured to adjust the word line recovery voltage provided to a selected word line to the target voltage level, based on the recovery control signals provided during a word line recovery operation following a program verify operation, and to reduce a program voltage rising time in a program execution operation period of a next program loop by adjusting the target voltage level.