Adjusting Voltage Differential in Memory String Drivers

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Solution Overview

Problem

The increasing memory density in semiconductor fabrication leads to longer RC time constants in conductive structures, resulting in slower access line voltage rise times, which hampers programming efficiency in memory devices like NAND flash memory.

Innovation Solution

The implementation of a voltage generation system with a voltage regulator that adjusts voltage differentials between access lines and control gates, using string drivers with high-voltage FETs and variable resistances to optimize voltage levels for faster programming pulses while preventing transistor damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If memory density is increased by decreasing feature sizes and utilizing three-dimensional array structures, then memory density is improved, but RC time constant increases causing slower access line voltage rise times

Engineering Contradiction:

Improvememory densityVSAvoidaccess line voltage rise time

Core Design Contradiction:

Quantity of substanceVSSpeed

Solution Approach 1:

The patent applies dynamics by making the voltage differential adjustable rather than fixed. The string driver circuit dynamically changes the voltage differential between the access line and control gate based on programming requirements, allowing optimization of both programming speed and transistor protection. This dynamic adjustment enables faster voltage rise times while maintaining safe operating conditions.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the voltage parameter by introducing an adjustable voltage differential mechanism. Instead of using a fixed voltage level, the system modifies the voltage differential between access line and control gate to optimize programming performance. This parameter change directly addresses the RC time constant issue by providing additional voltage drive capability.

Inventive Principle:

Principle #35Parameter changes

2Productivity

If higher voltage levels are applied to access lines for faster programming, then programming speed is improved, but transistor damage risk increases

Engineering Contradiction:

Improveprogramming speedVSAvoidtransistor safety

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent introduces an intermediary mechanism - the adjustable voltage differential - that mediates between the access line voltage and control gate voltage. This intermediary allows the system to achieve higher effective programming voltage while maintaining safe absolute voltage levels on transistors, thus protecting against damage while improving programming speed.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system dynamically adjusts the voltage differential to provide higher programming voltage only when needed, while maintaining safe operating margins. This dynamic control ensures that transistors are protected from excessive voltage stress while still enabling fast programming when conditions permit.

Inventive Principle:

Principle #15Dynamics

3Device complexity

If fixed voltage differentials are used in string drivers, then device simplicity is maintained, but programming efficiency is reduced due to inability to optimize for varying conditions

Engineering Contradiction:

Improvestring driver structureVSAvoidprogramming efficiency

Core Design Contradiction:

Device complexityVSProductivity

Solution Approach 1:

The patent transforms the fixed voltage differential into a dynamic, adjustable parameter. The string driver circuit incorporates mechanisms to vary the voltage differential based on programming progress and conditions, significantly improving programming efficiency without adding substantial complexity to the overall device structure.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the voltage differential parameter during programming operations to optimize performance. By adjusting this parameter based on verification results and programming stage, the system achieves higher programming efficiency while maintaining a relatively simple device architecture.

Inventive Principle:

Principle #35Parameter changes

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 enhances programming speed by reducing string driver resistance and maintaining transistor safety, thereby improving memory device performance and efficiency.

Implementation Method 1

string drivers with high-voltage FETs and variable resistances to optimize voltage levels

Methodology Applied

Scientific EffectField-effect transistor voltage control: Conduction (electrical)

Data Source

PatentUS11538529B2Adjusting voltage levels applied to a control gate of a string driver in a memory

Publication Date: 2022.12.27 MICRON TECHNOLOGY INC

AI summary

Methods of operating a memory, and memories having a controller configured to cause the memory to perform such methods, include applying a plurality of first voltage levels to an access line, applying a plurality of second voltage levels to a control gate of a string driver connected to the access line for a first portion of the plurality of first voltage levels with each second voltage level of the plurality of second voltage levels being greater than a respective first voltage level by a first voltage differential, and applying a plurality of third voltage levels to the control gate of the string driver for a second portion of the plurality of first voltage levels with each third voltage level of the plurality of third voltage levels being greater than a respective first voltage level by a second voltage differential less than the first voltage differential.