3D Stacked NAND Programming Without Channel Boosting
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Solution Overview
Problem
3D stacked memory devices face program disturb due to leakage of boosted channel potential, which is more susceptible in 3D structures compared to 2D devices, especially when inhibiting unselected NAND strings from programming.
Innovation Solution
Programming in 3D stacked non-volatile memory devices is achieved without boosting the channels of unselected NAND strings, instead, a series of increasing voltages are applied to selected bit lines, and unselected bit lines are held at ground or close to ground to prevent channel potential leakage, thereby avoiding program disturb.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If channel potential is boosted to inhibit unselected NAND strings from programming, then programming inhibition is achieved, but voltage leakage occurs causing program disturb
Solution Approach 1:
Instead of boosting the channel potential of unselected NAND strings to inhibit programming (conventional approach), the patent inverts the approach by applying voltages to word lines and bit lines to achieve inhibition without channel boosting. Specifically, a first voltage is applied to a selected word line and a second voltage to unselected word lines, while a third voltage is applied to the bit line, creating an electrical environment that prevents programming in unselected strings without requiring channel potential boosting.
Solution Approach 2:
The patent changes the voltage parameters applied to different lines (word lines and bit lines) to achieve programming inhibition. By dynamically adjusting the voltage levels on selected versus unselected word lines and the bit line, the patent creates appropriate electrical conditions that inhibit programming in unselected NAND strings without causing voltage leakage and program disturb.
2Ease of operation
If boosting voltage is applied to unselected NAND strings, then programming is inhibited, but leakage results in program disturb
Solution Approach 1:
The patent inverts the conventional approach by not boosting the channel potential of unselected NAND strings. Instead, it applies specific voltage combinations to word lines and bit lines to achieve programming inhibition, thereby maintaining ease of operation while avoiding the reliability issue of voltage leakage and program disturb.
Solution Approach 2:
The patent uses word lines and bit lines as intermediary elements to control programming. Rather than directly manipulating the channel potential of unselected NAND strings, the patent applies voltages to word lines (selected and unselected) and bit lines, which indirectly control the programming state without causing harmful voltage leakage.
3Reliability
If channel potential is boosted in 3D stacked memory, then unselected strings are inhibited from programming, but leakage susceptibility increases compared to 2D devices
Solution Approach 1:
The patent inverts the conventional channel-boosting approach by applying voltages to word lines and bit lines instead. This inversion eliminates the voltage leakage problem inherent in 3D stacked memory when channel boosting is used, while still achieving reliable programming inhibition in unselected NAND strings.
Solution Approach 2:
The patent applies different voltage conditions to different parts of the memory structure (selected versus unselected word lines, bit line). By creating localized voltage environments, the patent achieves programming inhibition in unselected strings without causing widespread voltage leakage that would affect the entire 3D stacked memory structure.
Data Source
AI summary
Programming NAND strings in a 3D stacked storage device to a conductive state. Storage elements may be erased by raising their Vt and programmed by lowering their Vt. Programming may include applying a series of increasing voltages to selected bit lines until the selected memory cell is programmed. Unselected bit lines may be held at about ground, or close to ground. The selected word line may be grounded, or be held close to ground. Unselected word lines between the selected word line and the bit line may receive about the selected bit line voltage. Unselected word lines between the source line and the selected word line may receive about half the selected bit line voltage. Programming may be achieved without boosting channels of unselected NAND strings to inhibit them from programming. Therefore, program disturb associated with leakage of boosted channel potential may be avoided.