Pre-charge Voltage Inhibits Unselected NAND Cell Programming
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Solution Overview
Problem
During NAND memory cell programming, unselected memory cells can experience unintended programming due to inadequate pre-charging of channels in NAND strings, leading to program disturb, especially when programming memory cells in vertical sub-blocks with valid data in adjacent sub-blocks.
Innovation Solution
Applying an overdrive voltage to programmed memory cells and a bypass voltage to unprogrammed memory cells during the pre-charge phase, while pre-charging the channels of unselected NAND strings from either the bit line, source line, or both, ensures adequate charging to prevent program disturb by boosting the channel voltage during the programming phase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pre-charging voltage is applied to NAND strings during programming, then program disturb in unselected memory cells is reduced, but device complexity increases due to additional voltage control circuits
Solution Approach 1:
The patent applies pre-charging voltage to NAND strings before the actual programming operation to elevate channel voltage in unselected memory cells. This preliminary action prevents program disturb by ensuring adequate channel voltage before programming pulses are applied, thereby protecting unselected cells without requiring complex real-time intervention circuits during programming.
Solution Approach 2:
The patent changes voltage parameters dynamically during different phases of the programming operation. Specifically, it applies different voltage levels (e.g., Vcc1, Vcc2) to bit lines and source lines depending on whether the phase is pre-charging or actual programming. This parameter change approach enables simple circuit implementation while achieving reliable program disturb prevention through voltage timing control.
2Reliability
If channel voltage is boosted during programming phase, then unselected memory cells are protected from programming, but energy consumption increases
Solution Approach 1:
The patent employs periodic voltage application in distinct phases: a pre-charging phase where voltage is applied to elevate channel potential, followed by a programming phase where programming pulses are applied. This periodic action pattern allows energy-efficient protection by applying boost voltage only when necessary (during pre-charging) rather than continuously during the entire programming operation.
Solution Approach 2:
By applying pre-charging voltage before the programming phase, the patent prepares unselected memory cells in advance by elevating their channel voltage. This preliminary action reduces the energy required during the actual programming phase because the channel is already charged, minimizing the additional energy needed to maintain protection while reducing overall energy consumption.
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 prevents or reduces program disturb in unselected memory cells, allowing for reliable programming of memory cells in middle vertical sub-blocks even when valid data exists in adjacent sub-blocks, by ensuring the channels of unselected NAND strings are adequately charged.
Implementation Method 1
pre-charging the channels of unselected NAND strings from either the bit line, source line, or both, ensures adequate charging to prevent program disturb by boosting the channel voltage during the programming phase
Data Source
AI summary
Techniques are provided for pre-charging NAND strings during a programming operation. The NAND strings are in a block that is divided into vertical sub-blocks. During a pre-charge phase of a programming operation, an overdrive voltage is applied to some memory cells and a bypass voltage is applied to other memory cells. The overdrive voltage allows the channel of an unselected NAND string to adequately charge during the pre-charge phase. Adequate charging of the channel helps the channel voltage to boost to a sufficient level to inhibit programming of an unselected memory cell during a program phase. Thus, program disturb is prevented, or at least reduced. The technique allows, for example, programming of memory cells in a middle vertical sub-block without causing program disturb of memory cells that are not to receive programming.