Dual-Bit Flash Memory Cell Erasing Residual Electrons

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Solution Overview

Problem

Conventional dual-bit flash memory cells face performance and reliability issues due to residual electrons in the charge storage layer after programming, leading to non-uniform threshold voltages and degraded device operation.

Innovation Solution

The dual-bit memory cell employs physically and electrically separated charge storage regions with an isolation region, allowing for precise injection of electrons or holes using Fowler-Nordheim tunneling and band-to-band hot hole programming techniques to erase and program the memory, respectively, ensuring no residual electrons remain in the isolation region.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional dual-bit flash memory cells use a single charge storage layer without isolation regions, then the device complexity is reduced and manufacturing is easier, but residual electrons remain in the charge storage layer after programming causing non-uniform threshold voltages and degraded device operation

Engineering Contradiction:

Improvedevice operation uniformityVSAvoidcharge storage region structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The charge storage layer is segmented into two physically and electrically separated charge storage regions by inserting an isolation region between them. This segmentation allows independent control and charge injection into each region, preventing residual electron interference and achieving uniform threshold voltages across both bits, thereby resolving the reliability issue without excessive complexity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The isolation region is extracted from the conventional single charge storage layer structure and placed between the two charge storage regions. This extracted isolation region actively removes or prevents residual electrons from affecting both charge storage regions, eliminating the harmful effect of non-uniform threshold voltages while maintaining a manageable device structure

Inventive Principle:

Principle #2Taking out (Extraction)

2Manufacturing precision

If Fowler-Nordheim tunneling and band-to-band hot hole programming techniques are used with isolated charge storage regions, then programming precision and erasure completeness are improved, but the manufacturing process becomes more complex

Engineering Contradiction:

Improvecharge injection precisionVSAvoidmemory cell fabrication

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

Different programming and erasing techniques are applied locally to different charge storage regions based on their specific requirements. Fowler-Nordheim tunneling is used for complete erasure of residual electrons in the isolated regions, while band-to-band hot hole programming is used for precise charge injection into specific regions. This localized application of techniques achieves high manufacturing precision without requiring complete redesign of the entire fabrication process

Inventive Principle:

Principle #3Local quality

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 the reliability and uniformity of the memory cell operation by eliminating residual electrons, resulting in improved performance and a more uniform transistor structure with consistent threshold voltages across the charge storage regions.

Implementation Method 1

The charge storage regions can be physically and electrically separated by an isolation region disposed between the charge storage regions

Methodology Applied

Scientific EffectPhysical separation:

Implementation Method 2

Electron injection can be accomplished, for example, by Fowler-Nordheim (FN) electron tunneling technique in which electrons are tunneled into at least one of the charge storage regions to erase the memory

Methodology Applied

Scientific EffectFowler-Nordheim tunneling:

Implementation Method 3

Hole injection can be accomplished, for example, using a band-to-band hot hole (BTBHH) programming technique which involves applying a positive bias voltage to a source or drain region of a substrate and applying a negative voltage to a gate to pull holes from either the source region or the drain region into at least one of the charge storage regions

Methodology Applied

Scientific EffectBand-to-band hot hole programming:

Data Source

PatentUS7394702B2Methods for erasing and programming memory devices

Publication Date: 2008.07.01 INFINEON TECHNOLOGIES LLC

AI summary

A dual-bit memory device includes a first charge storage region spaced apart from a second charge storage region by an isolation region. Techniques for erasing a memory can be provided in which electrons can be injected into the charge storage regions to erase the charge storage regions. Other techniques for programming a memory can be provided in which holes can be injected into at least one of the charge storage regions to program the charge storage regions.