NAND Channel Pre-charge Maintenance via Word Line Voltage Control
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Solution Overview
Problem
In semiconductor memory devices, particularly in 3D NAND structures, maintaining channel pre-charge during programming operations while minimizing the risk of program disturb is challenging due to voltage gradients and temperature variations, which can lead to unintended programming of memory cells.
Innovation Solution
The solution involves adjusting the voltages of source side word lines during the transition period from the pre-charge phase to a pass voltage, either directly or through a gradual decrease and increase, based on risk factors such as temperature, position, and program voltage, to reduce channel gradients and prevent program disturb.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage is applied to maintain channel pre-charge during programming operations, then channel pre-charge is maintained, but program disturb occurs due to voltage gradients
Solution Approach 1:
The patent applies different voltage levels to different word lines based on their position and the state of adjacent memory cells. Specifically, source side word lines are maintained at higher voltages while drain side word lines are at lower voltages, creating localized voltage conditions that maintain channel pre-charge where needed while preventing program disturb in other regions.
Solution Approach 2:
The patent dynamically adjusts voltage parameters during the programming operation. The voltage on source side word lines is increased relative to drain side word lines during the transition period, and the magnitude of voltage swing is controlled based on temperature and position to maintain channel pre-charge while minimizing program disturb.
2Productivity
If voltage swing is increased to program memory cells, then programming speed improves, but channel pre-charge is lost and program disturb increases
Solution Approach 1:
The patent applies pre-charge voltage to source side word lines before the programming pulse is applied to drain side word lines. This preliminary action ensures that the channel is already charged and ready for programming, allowing the programming pulse to be applied without losing channel pre-charge or causing program disturb.
Solution Approach 2:
The patent uses dynamic voltage adjustment where the voltage on source side word lines is increased during the transition period from pre-charge to programming phase. This dynamic adjustment allows the system to adapt to temperature and position variations, maintaining channel pre-charge while enabling effective programming.
3Reliability
If temperature compensation is applied to prevent program disturb, then program disturb is reduced, but additional control complexity is introduced
Solution Approach 1:
The patent implements temperature sensing that provides feedback to the voltage control circuitry. Based on the sensed temperature, the system adjusts the voltage swing magnitude on source side word lines, applying larger voltage swings at lower temperatures and smaller voltage swings at higher temperatures to maintain channel pre-charge while preventing program disturb.
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 maintains channel pre-charge and reduces the likelihood of program disturb, ensuring accurate programming and data integrity by optimizing voltage swings and gradients across memory cells.
Implementation Method 1
maintaining channel pre-charge in program operation... adjusting the voltages of source side word lines during the transition period... to reduce channel gradients and prevent program disturb
Data Source
AI summary
Techniques are described for maintaining a pre-charge voltage in a NAND string in a program operation. After a pre-charge voltage is applied to the channel of a NAND string, the word line voltages are controlled to avoid a large channel gradient which generates electron-hole pairs, where the electrons can pull down the channel boosting level on the drain side of the selected word line. In one approach, the word line voltages of a group of one or more source side word lines adjacent to the selected word line are increased directly from the level used during pre-charge to a pass voltage. The word line voltages of other source side word lines, and of drain side word lines, can be decreased and then increased to the pass voltage to provide a large voltage swing which couples up the channel.