NAND Program Refresh Using GIDL to Recover Read Window Budget

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Solution Overview

Problem

Existing memory devices face challenges in increasing the number of bits stored per cell without expanding the read window budget (RWB) due to narrow threshold voltage distributions and overlapping distributions, leading to reduced read margins.

Innovation Solution

Implementing program refresh with gate-induced drain leakage (GIDL) to tighten threshold voltage distributions and recover RWB by applying controlled bias voltages to generate positive charge carriers to neutralize negative charge carriers, thereby enhancing read margins.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If the number of bits stored per cell is increased, then the storage capacity is improved, but the read window budget (RWB) is reduced due to overlapping threshold voltage distributions

Engineering Contradiction:

Improvenumber of bits stored per cellVSAvoidread window budget

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent applies parameter changes by modifying the threshold voltage distribution through program refresh operations. By applying program pulses to selected memory cells and using GIDL to generate positive charge carriers, the threshold voltage distribution is tightened and shifted, thereby recovering the read window budget while maintaining the increased storage capacity.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful effect of GIDL (gate-induced drain leakage), which is typically considered a source of errors in memory devices, into a beneficial mechanism. By intentionally exploiting GIDL to generate positive charge carriers during program refresh, the patent neutralizes negative charge carriers and tightens threshold voltage distributions, thus improving read margins while maintaining high storage capacity.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Reliability

If the threshold voltage distribution is tightened to recover RWB, then the read margin is improved, but additional program refresh operations are required

Engineering Contradiction:

Improveread marginVSAvoidprogram refresh operations

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent implements self-service by using the program refresh operation itself to generate the necessary positive charge carriers through GIDL. The same operation that tightens the threshold voltage distribution also provides the charge carriers needed for neutralization, eliminating the need for separate operations and reducing overall time loss.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent ensures continuity of useful action by integrating the GIDL-based charge carrier generation directly into the program refresh operation. Rather than performing discrete steps, the patent maintains continuous action where the program refresh simultaneously achieves both threshold voltage tightening and charge carrier generation, improving efficiency.

Inventive Principle:

Principle #20Continuity of useful action

3Manufacturing precision

If GIDL is used to generate positive charge carriers, then the threshold voltage distribution is tightened, but controlled bias voltages must be applied

Engineering Contradiction:

Improvethreshold voltage distributionVSAvoidbias voltage control

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The patent applies universality by using the control gate and bit line, which are standard components for memory operations, to also generate GIDL and positive charge carriers. This multi-functional use of existing components avoids adding complex dedicated bias voltage generation circuitry, thereby tightening threshold voltage distributions without significantly increasing device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 allows for storing additional bits per cell while maintaining or improving read margins, thus enhancing memory device performance and reliability.

Implementation Method 1

gate-induced drain leakage (GIDL) to tighten threshold voltage distributions and recover RWB by applying controlled bias voltages to generate positive charge carriers to neutralize negative charge carriers

Methodology Applied

Scientific EffectGate-induced drain leakage (GIDL):

Data Source

PatentUS12505897B2Program refresh with gate-induced drain leakage

Publication Date: 2025.12.23 MICRON TECHNOLOGY INC

AI summary

A memory device includes a memory array including wordlines and at least one string of cells. Each cell of the at least one string of cells is addressable by a respective wordline. The memory device further includes control logic, operatively coupled to the memory array, to perform operations including generating gate-induced drain leakage (GIDL) with respect to the at least one string of cells, and causing a grounding voltage to be applied to a set of wordlines to ground each cell of the at least one string of cells addressable by each wordline of the set of wordlines. The grounding voltage applied to the set of wordlines enables transport of positive charge carriers generated by the GIDL. In some embodiments, the positive charge carriers neutralize a buildup of negative charge carriers generated during a seeding phase of a program refresh operation.