Nonvolatile Memory Programming Method Using Periodic Charge Injection

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Solution Overview

Problem

Conventional nonvolatile semiconductor memory devices with trap layers face data retention characteristic deterioration due to charge diffusion and binding with surrounding charges, leading to reduced access speed and erroneous data read, especially with increased programming or erasing cycles.

Innovation Solution

Implementing a programming or erasing method that includes a first charge injection followed by a wait time and a second charge injection, ensuring that the charge injection reaches a given threshold voltage, thereby reducing initial charge loss and improving data retention by minimizing subsequent binding between electrons and holes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If charge injection is performed continuously without wait time, then programming speed is improved, but data retention characteristic deteriorates due to charge diffusion and binding

Engineering Contradiction:

Improveprogramming speedVSAvoiddata retention characteristic

Core Design Contradiction:

SpeedVSReliability

Solution Approach 1:

The patent applies periodic action by dividing continuous charge injection into discrete pulses separated by wait periods. The programming operation uses multiple programming pulses with predetermined wait periods inserted between them, allowing periodic charge injection that prevents excessive diffusion and binding while maintaining programming effectiveness over time.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The patent implements preliminary action by performing the first charge injection to reach a given threshold voltage before performing subsequent charge injection. This preliminary charge injection establishes an initial state that prevents excessive charge diffusion and binding during subsequent operations, thereby improving data retention characteristic.

Inventive Principle:

Principle #10Preliminary action

2Quantity of substance

If multiple programming or erasing cycles are performed, then memory capacity is improved, but access speed reduces and erroneous data reads increase

Engineering Contradiction:

Improvememory capacityVSAvoidaccess speed

Core Design Contradiction:

Quantity of substanceVSSpeed

Solution Approach 1:

The patent uses periodic action with multiple programming pulses separated by wait periods to perform multiple programming or erasing cycles. This periodic approach allows charge to stabilize between cycles, preventing cumulative diffusion and binding effects that would otherwise reduce access speed and increase erroneous reads, thereby maintaining memory capacity without sacrificing speed.

Inventive Principle:

Principle #19Periodic action

3Productivity

If charge injection reaches high threshold voltage immediately, then programming efficiency is improved, but subsequent charge binding increases reducing data retention

Engineering Contradiction:

Improveprogramming efficiencyVSAvoiddata retention

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies preliminary action by performing an initial charge injection to reach a given threshold voltage, then inserting a wait period before subsequent charge injection. This preliminary action establishes a stable charge state that prevents excessive binding, allowing programming efficiency to be maintained while improving data retention through the intermediate stabilization period.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements periodic action by using multiple programming pulses with wait periods between them. This periodic structure allows the threshold voltage to be adjusted incrementally with stabilization periods, preventing the excessive charge binding that occurs with continuous high-voltage injection while maintaining programming efficiency over multiple cycles.

Inventive Principle:

Principle #19Periodic action

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 data retention characteristic of memory cells by stabilizing the memory cell threshold voltage over time, improving access speed and reducing erroneous data reads, even with multiple programming or erasing cycles.

Implementation Method 1

electric charge (electrons and holes) is trapped by injection of the charge in a discrete trap layer

Methodology Applied

Scientific EffectCharge trapping:

Implementation Method 2

part of electrons moving from the second impurity region 1804 to the first impurity region 1803 is made hot with a high electric field in the neighborhood of the first impurity region 1803, and thus locally injected into the trap layer 1806

Methodology Applied

Scientific EffectHot carrier injection:

Implementation Method 3

part of holes generated due to inter-band tunneling inside the first impurity region 1803 is made hot with a high electric field in the neighborhood of the first impurity region 1803, and thus locally injected into the trap layer 1806

Methodology Applied

Scientific EffectInter-band tunneling:

Data Source

PatentUS7460410B2Nonvolatile semiconductor memory device and programming or erasing method therefor

Publication Date: 2008.12.02 PANASONIC SEMICON SOLUTIONS CO LTD

AI summary

In a nonvolatile memory cell having a trap layer, programming or erasing is made in a sequence of first charge injection with a given wait time being secured and second charge injection executed after the first charge injection. Surrounding charge that deteriorates the data retention characteristic is reduced by use of initial variation occurring immediately after programming (charge loss phenomenon due to binding of injected charge with the surrounding charge in an extremely short time), and then the charge loss due to the initial variation is compensated, to thereby improve the data retention characteristic.