Flash Memory Program Method Uniform Channel Boosting
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Solution Overview
Problem
Flash memory devices experience program disturbance during operations, particularly when storing 2-bit data, due to varying channel boosting characteristics across memory cells, leading to inconsistent program characteristics and threshold voltage changes in neighboring cells.
Innovation Solution
The method involves uniformly precharging channel regions within a string by applying a ground voltage to one bit line connected to programmed cells and a program-inhibited voltage to another bit line connected to program-inhibited cells, generating channel boosting only in the string with program-inhibited cells, thereby preventing threshold voltage changes in program-inhibited cells during the program operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If different voltages are applied to bit lines connected to to-be-programmed cells and program-inhibited cells, then program operation can be performed on specific cells, but channel boosting characteristics vary across memory cells causing program disturbance
Solution Approach 1:
The patent applies a preliminary voltage to the bit line connected to program-inhibited cells before the program operation begins. This preliminary voltage ensures that the channel region in the string containing program-inhibited cells is precharged to a level that prevents unwanted electron injection during the subsequent program operation, thereby eliminating program disturbance while maintaining the ability to selectively program specific cells
2Manufacturing precision
If channel boosting is generated during program operation, then program characteristics are improved, but threshold voltage of program-inhibited cells changes due to varying boosting characteristics
Solution Approach 1:
The patent applies a preliminary voltage to the bit line connected to program-inhibited cells before the program operation to counteract the potential harmful effect of channel boosting. This preliminary voltage precharges the channel region to a level that prevents electron injection into the floating gate of program-inhibited cells during the program operation, thereby maintaining threshold voltage stability while allowing channel boosting to occur in strings with to-be-programmed cells
Data Source
AI summary
In a program method of a flash memory device where memory cells within a string are turned on to electrically connect channel regions, all of the channel regions within a second string are precharged uniformly by applying a ground voltage to a first bit line connected to a first string including to-be-programmed cells and a program-inhibited voltage to a second bit line connected to the second string including program-inhibited cells. If a program operation is executed, channel boosting occurs in the channel regions within the second string including the program-inhibited cells. Accordingly, a channel boosting potential can be increased and a program disturbance phenomenon, in which the threshold voltage of program-inhibited cells is changed, can be prevented.