Memory Device Discharge Voltage Pulse Program Disturb
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Solution Overview
Problem
Program disturb occurs in memory devices due to high gate-to-channel voltage and hot carrier injection, causing unintended programming of unselected memory cells during the programming of selected cells in NAND strings, leading to changes in threshold voltage and data state shifts.
Innovation Solution
A discharge operation is performed at the start of a program loop to remove residue electrons from the channel region, reducing the likelihood of program disturb by applying a voltage pulse to a set of drain-side word lines while holding unselected word lines at ground, which helps in the subsequent pre-charge operation and reduces electron injection into the charge trapping layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high gate-to-channel voltage is applied during programming, then programming efficiency is improved, but program disturb increases causing unintended programming of unselected memory cells
Solution Approach 1:
A discharge operation is performed at the start of each program loop to remove residue electrons from the channel region before the programming operation begins. This preliminary action reduces the likelihood of program disturb by eliminating accumulated electrons that could be inadvertently injected into unselected memory cells during subsequent high-voltage programming operations.
Solution Approach 2:
The discharge operation is applied periodically at the beginning of each program loop rather than continuously. This periodic discharge maintains channel cleanliness throughout the programming process, ensuring that residue electrons are removed at regular intervals while minimizing the impact on overall programming efficiency.
2Reliability
If voltage pulse is applied to drain-side word lines during discharge operation, then residue electron removal is improved, but device complexity increases
Solution Approach 1:
The discharge operation selectively applies voltage pulses to specific drain-side word lines (WL0-WL7) while leaving other word lines at ground potential. This segmentation approach focuses the discharge effect on the most critical regions where residue electrons accumulate, improving electron removal effectiveness while avoiding the need to control all word lines simultaneously.
Solution Approach 2:
Different voltage conditions are applied to different sets of word lines during the discharge operation. Drain-side word lines receive voltage pulses to effectively remove electrons, while source-side word lines remain at ground. This local differentiation optimizes the discharge effect in regions where it is most needed without unnecessarily complicating the control of the entire memory array.
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
The discharge operation effectively reduces the number of source-side residue electrons, minimizing program disturb and maintaining channel boosting, thereby improving data integrity and reducing the risk of data state shifts during programming.
Implementation Method 1
Program disturb occurs in memory devices due to high gate-to-channel voltage and hot carrier injection, causing unintended programming of unselected memory cells
Data Source
AI summary
Techniques are disclosed for reducing an injection type of program disturb in a memory device. In one aspect, a discharge operation is performed at the start of a program loop. This operation discharges residue electrons from the channel region on the source side of the selected word line, WLn, to the channel region on the drain side of WLn. As a result, in a subsequent channel pre-charge operation, the residue electrons can be more easily removed from the channel. The discharge operation involves applying a voltage pulse to WLn and a first set of drain-side word lines which is adjacent to WLn. The remaining unselected word lines may be held at ground during the voltage pulse.