Data State-Dependent Channel Boosting in NAND Flash Memory

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Solution Overview

Problem

As memory devices are scaled down, electromagnetic coupling effects become significant, leading to program disturb and undesirable widening of threshold voltage distributions in NAND flash memory devices, making it challenging to accurately read and program storage elements.

Innovation Solution

Optimizing channel boosting techniques by tailoring the boosting levels based on the data state of unselected storage elements, using different voltages for bit lines, drain-side select gates, and dummy storage elements to inhibit unselected storage elements from further programming, thereby reducing electromagnetic coupling effects and maintaining accurate threshold voltage distributions.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If channel boosting is applied to inhibit unselected storage elements during programming, then program disturb is prevented, but electromagnetic coupling effects cause undesirable widening of threshold voltage distributions

Engineering Contradiction:

Improveprogram disturb preventionVSAvoidthreshold voltage distribution width

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent applies different boosting voltages to different channel regions based on the data state of unselected storage elements. Channels associated with storage elements in lower data states receive higher boosting voltages, while channels associated with storage elements in higher data states receive lower boosting voltages. This localized differentiation prevents program disturb in lower states while minimizing threshold voltage widening in higher states.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent dynamically adjusts the boosting voltage parameter based on the data state of unselected storage elements. By changing the boosting voltage level according to the specific data state (e.g., higher voltage for lower states, lower voltage for higher states), the system optimizes the balance between preventing program disturb and minimizing threshold voltage distribution widening.

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If data state-dependent channel boosting is implemented, then programming accuracy is enhanced, but device complexity increases due to multiple voltage levels and state determination requirements

Engineering Contradiction:

Improveprogramming accuracyVSAvoidcontrol circuit complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent determines the data state of unselected storage elements before applying the program pulse, and pre-calculates the appropriate boosting voltage level based on this determination. This preliminary action allows the control circuit to prepare the correct boosting voltage in advance, simplifying the real-time control requirements during the actual programming operation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent divides the set of unselected storage elements into different groups based on their data states, and applies different boosting schemes to each group. This segmentation allows the control circuit to manage complexity by handling each data state group separately with predetermined boosting strategies, rather than managing all storage elements uniformly.

Inventive Principle:

Principle #1Segmentation

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 program disturb and narrows the threshold voltage distributions, enhancing the programming accuracy and endurance of NAND flash memory devices by ensuring appropriate channel boosting levels are applied based on the data state of inhibited storage elements.

Implementation Method 1

electromagnetic coupling effects in memory devices are becoming increasingly important as memory device dimensions are scaled down

Methodology Applied

Scientific EffectElectromagnetic coupling:

Implementation Method 2

causing electrons from the channel of a storage element to be injected into the floating gate

Methodology Applied

Scientific EffectElectron injection:

Data Source

PatentUSRE45520E1Data state-dependent channel boosting to reduce channel-to-floating gate coupling in memory

Publication Date: 2015.05.19 SAMSUNG ELECTRONICS CO LTD

AI summary

In a programming operation, selected storage elements on a selected word line are programmed while unselected storage elements on the selected word line are inhibited from programming by channel boosting. To provide a sufficient but not excessive level of boosting, the amount of boosting can be set based on a data state of the unselected storage element. A greater amount of boosting can be provided for a lower data state which represents a lower threshold voltage and hence is more vulnerable to program disturb. A common boosting scheme can be used for groups of multiple data states. The amount of boosting can be set by adjusting the timing and magnitude of voltages used for a channel pre-charge operation and for pass voltages which are applied to word lines. In one approach, stepped pass voltages on unselected word lines can be used to adjust boosting for channels with selected data states.