Flash Memory Word Line Enable Method for Program Disturb Reduction
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Solution Overview
Problem
As the integration density of flash memory devices increases, capacitive coupling between adjacent signal lines becomes more significant, leading to unintended programming of unselected memory cells during the programming process, known as program disturb, which conventional self-boosting schemes struggle to fully prevent.
Innovation Solution
A method involving a stepwise increase in block word line voltage during the programming period, using a block word line voltage generator circuit to control the slope of the pass and program voltages applied to word lines, reducing capacitive coupling and preventing soft programming of unselected memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If integration density is increased, then memory capacity is improved, but capacitive coupling between adjacent signal lines increases causing program disturb
Solution Approach 1:
The patent applies preliminary action by pre-charging the source of the string selection transistor to Vcc-Vth before applying the program voltage to the selected word line. This preliminary charging ensures that the string selection transistor is already in a blocked state when the program voltage is applied, preventing capacitive coupling from turning on the transistor and causing program disturb in unselected memory cells
Solution Approach 2:
The patent employs dynamics by controlling the timing and sequence of voltage applications. The source charge voltage is applied first to establish the blocked state, and only after this preliminary action is the program voltage applied to the selected word line. This dynamic sequencing ensures that even with increased integration density, the string selection transistor remains blocked during programming operations
2Object-affected harmful factors
If self-boosting scheme is used, then program disturb is reduced, but soft programming occurs due to voltage boosting on string selection line
Solution Approach 1:
The patent applies preliminary anti-action by pre-charging the source of the string selection transistor to Vcc-Vth before applying the program voltage. This preliminary action creates a blocked state that counteracts the harmful effect of voltage boosting on the string selection line caused by capacitive coupling during self-boosting operations, preventing soft programming of program inhibited cells
Solution Approach 2:
The source charge voltage is applied in advance to establish the blocked state of the string selection transistor before the program voltage is applied to the selected word line. This preliminary action ensures that even when voltage boosting occurs on the string selection line during self-boosting, the transistor remains blocked and prevents charge leakage that would cause soft programming
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 suppresses capacitive coupling between signal lines, minimizing the risk of unintended programming of unselected memory cells and maintaining the integrity of programmed data by adjusting the voltage slope applied to word lines.
Implementation Method 1
as the integration density is increased, the intervals between adjacent signal lines are reduced, thereby increasing the possibility of coupling between the adjacent signal lines
Implementation Method 2
Fowler-Nordheim (F-N) tunneling cannot take place between the floating gate and the channel, thereby keeping the program inhibited cell transistor in the initial erased state
Data Source
AI summary
In one aspect, a word line enable method in a flash memory device includes driving a signal line corresponding to a selected word line with a word line voltage, and stepwise increasing a gate voltage of a switch transistor connected between the selected word line and the signal line during a program execute period.