Split Gate Memory Programming via SSI and CHISEL

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Solution Overview

Problem

Split gate memories face challenges in data retention due to current leakage from nanocrystals, which affects their reliability, especially in applications requiring long-term charge storage, such as automotive uses.

Innovation Solution

A programming technique is employed that differentiates between two portions of the charge storage layer under the control gate, utilizing source-side injection (SSI) and channel-initiated secondary electron (CHISEL) programming to achieve higher threshold voltages and improve data retention by selectively accumulating electrons in nanocrystals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If nanocrystals are used as charge storage medium, then manufacturing cost is reduced and partial leakage tolerance is improved, but data retention deteriorates due to current leakage

Engineering Contradiction:

Improvedata retentionVSAvoidcurrent leakage

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The charge storage layer is segmented into multiple nanocrystals distributed across the control gate. While individual nanocrystals leak charge, the distributed architecture ensures that only a portion of the total storage capacity is affected at any given time, allowing the memory to maintain reliable operation despite leakage in specific locations.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies dual programming techniques (SSI and CHISEL) that change the electrical parameters and programming sequences to achieve higher threshold voltages. By varying the programming approach and achieving higher Vt levels, the memory's resistance to leakage effects is enhanced, thereby improving data retention.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If higher threshold voltage is achieved through programming, then data retention is improved, but programming complexity increases

Engineering Contradiction:

Improvedata retentionVSAvoidprogramming technique complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The programming process is segmented into two distinct techniques: Source-Side Injection (SSI) and Channel-Initiated Secondary Electron (CHISEL) programming. Each technique targets specific portions of the charge storage layer and uses different physical mechanisms. This segmentation allows the system to achieve high threshold voltages by combining the advantages of both methods without requiring a single complex programming approach.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the charge storage layer are programmed using different techniques optimized for their specific locations and characteristics. The SSI technique is applied to certain regions while CHISEL is applied to others, with each method tailored to achieve optimal threshold voltage enhancement in its target area, thereby improving overall data retention without uniformly increasing complexity throughout the entire programming 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 method enhances data retention by increasing the threshold voltage, extending the time before leakage lowers it to an unreliable level, thus making split gate memories more suitable for applications requiring long-term data storage.

Implementation Method 1

Methodology Applied

Scientific EffectElectron accumulation:

Implementation Method 2

channel-initiated secondary electron (CHISEL) programming to achieve higher threshold voltages

Methodology Applied

Scientific EffectSecondary electron emission:

Data Source

PatentUS8953378B2Split gate programming

Publication Date: 2015.02.10 NXP USA INC

AI summary

A method for programming a split gate memory cell includes performing a first programming of the split gate memory cell in a first programming cycle of the split gate memory cell; and, subsequent to the performing the first programming of the split gate memory cell, performing a second programming of the split gate memory cell in the first programming cycle, wherein the first programming is characterized as one of source-side injection (SSI) programming and channel-initiated secondary electron (CHISEL) programming, and the second programming is characterized as the other of SSI programming and CHISEL programming.