EEPROM Programming via Conduction Threshold Feedback

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Solution Overview

Problem

Conventional EEPROM memory cells using the Fowler-Nordheim effect for programming and erasing suffer from over-programming and dispersion of conduction thresholds, leading to reduced memory cell lifetime and inefficiency in storing multiple bits per cell.

Innovation Solution

A method that controls the charge on the floating gate in real-time during programming, allowing the memory cell to go into conduction and setting a specific conduction threshold by adjusting the control gate voltage, enabling multi-level memory storage without over-programming and improving cell endurance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional fixed-duration write cycle is used, then programming is completed, but over-programming occurs causing excessive charge on floating gate which reduces memory cell lifetime

Engineering Contradiction:

Improvememory cell lifetimeVSAvoidexcessive charge on floating gate

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The patent implements feedback control by monitoring the conduction threshold of the memory cell during programming and adjusting the programming voltage dynamically. When the conduction threshold reaches the target value, programming is automatically stopped, preventing over-programming and excessive charge accumulation on the floating gate, thereby extending memory cell lifetime.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent transforms the static fixed-duration programming approach into a dynamic process where programming voltage and duration are adjusted in real-time based on the actual conduction threshold of the memory cell. This dynamic adaptation prevents over-programming while ensuring accurate multi-level data storage.

Inventive Principle:

Principle #15Dynamics

2Manufacturing precision

If conventional fixed-duration write cycle is used, then programming is completed, but dispersion of conduction thresholds occurs across different programmed memory cells

Engineering Contradiction:

Improveconduction threshold precisionVSAvoidfixed programming duration

Core Design Contradiction:

Manufacturing precisionVSLoss of time

Solution Approach 1:

The patent uses feedback control to monitor the conduction threshold of each memory cell during programming and terminates programming when the target threshold is reached. This ensures precise conduction threshold control across all programmed cells, eliminating the threshold dispersion caused by fixed-duration programming.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent performs preliminary characterization to establish the relationship between control gate voltage and conduction threshold before programming. This preliminary action enables accurate prediction of required programming parameters, ensuring precise conduction threshold control and reducing variability across memory cells.

Inventive Principle:

Principle #10Preliminary action

3Quantity of substance

If multi-level memory storage is implemented, then multiple bits per cell are stored, but control of charge quantity on floating gate becomes more difficult

Engineering Contradiction:

Improvecharge quantity on floating gateVSAvoidprogramming control complexity

Core Design Contradiction:

Quantity of substanceVSDevice complexity

Solution Approach 1:

The patent utilizes parameter changes by varying the control gate voltage to different discrete levels, where each voltage level corresponds to a specific conduction threshold and represents a distinct data value. This enables multi-level memory storage by controlling the quantity of charge on the floating gate through precise voltage modulation, achieving multiple bits per cell with manageable complexity.

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 prevents over-programming, enhances memory cell endurance, and allows for efficient storage of multiple bits per cell by controlling the charge on the floating gate, improving the programming process and reducing the dispersion of conduction thresholds.

Implementation Method 1

The programming is carried out by the Fowler-Nordheim effect and comprises the injection by tunnel effect of electrons from the floating gate towards the drain

Methodology Applied

Scientific EffectFowler-Nordheim effect:

Implementation Method 2

the injection by tunnel effect of electrons from the floating gate towards the drain

Methodology Applied

Scientific EffectTunnel effect:

Implementation Method 3

the erasing, which is also carried out by the Fowler-Nordheim effect, comprises an injection by tunnel effect of electrons from the drain towards the floating gate

Methodology Applied

Scientific EffectFowler-Nordheim effect:

Implementation Method 4

comprises an injection by tunnel effect of electrons from the drain towards the floating gate

Methodology Applied

Scientific EffectTunnel effect:

Data Source

PatentUS9899090B2Method for writing into and reading a multi-levels EEPROM and corresponding memory device

Publication Date: 2018.02.20 STMICROELECTRONICS INT NV

AI summary

During a phase of programming the cell, a first voltage is applied to the source region and a second voltage, higher than the first voltage, is applied to the drain region until the cell is put into conduction. The numerical value of the item of data to be written is controlled by the level of the control voltage applied to the control gate and the item of data is de facto written with the numerical value during the putting into conduction of the cell. The programming is then stopped.