Flash Memory Radiation Hardening via Program-Erase Cycling

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Solution Overview

Problem

Commercial NAND flash memory is not adequately radiation-hardened for space applications due to its limited capacity and high cost, and existing radiation hardening techniques compromise memory density for reliability, while flash memory faces reliability issues with ionizing radiation.

Innovation Solution

Implementing accelerated aging through controlled program-erase cycling in flash memory to induce trap states in tunnel oxides, improving ionizing radiation tolerance without significantly reducing memory density or increasing costs.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If accelerated aging through program-erase cycling is performed to harden flash memory to radiation, then radiation tolerance is improved by more than 25%, but memory density and retention characteristics deteriorate

Engineering Contradiction:

Improveradiation toleranceVSAvoidmemory density

Core Design Contradiction:

ReliabilityVSQuantity of substance

Solution Approach 1:

The patent applies parameter changes by modifying the electrical characteristics of the flash memory cell through controlled program-erase cycling. This process alters the threshold voltage distribution and creates trap states in the oxide layers, which changes the memory's radiation response characteristics. The parameter changes in the memory cell's electrical properties enable improved radiation tolerance while maintaining acceptable memory density

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent implements preliminary action by performing accelerated aging through program-erase cycling before the memory is deployed to space environments. This pre-treatment process creates a more robust memory structure that is pre-hardened to radiation effects, allowing the memory to withstand space radiation better than unconditioned memory would

Inventive Principle:

Principle #10Preliminary action

2Reliability

If program-erase cycling is increased to induce trap states in tunnel oxides, then ionizing radiation tolerance improves, but data retention characteristics worsen

Engineering Contradiction:

Improveionizing radiation toleranceVSAvoiddata retention

Core Design Contradiction:

ReliabilityVSDuration of action of stationary object

Solution Approach 1:

The patent utilizes parameter changes by controlling the distribution of trap states in the oxide layers through specific program-erase cycling protocols. This creates an optimal balance where trap states are sufficient to capture radiation-induced charges and prevent floating gate charge loss, while not so numerous as to create excessive leakage paths that would degrade data retention

Inventive Principle:

Principle #35Parameter changes

3Quantity of substance

If commercial NAND flash memory is used for space applications, then storage capacity and cost are improved, but radiation hardness is insufficient

Engineering Contradiction:

Improvestorage capacityVSAvoidradiation hardness

Core Design Contradiction:

Quantity of substanceVSObject-affected harmful factors

Solution Approach 1:

The patent applies the blessing in disguise principle by converting the harmful effect of ionizing radiation into a beneficial hardening mechanism. By exposing the memory to controlled radiation levels or equivalent electrical stress that mimics radiation effects, the memory structure develops increased resistance to subsequent radiation exposure, transforming a vulnerability into a strength

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent employs parameter changes to modify the electrical and physical characteristics of the flash memory cell through accelerated aging processes. These parameter changes in threshold voltage, charge trapping characteristics, and oxide layer properties enable commercial flash memory to achieve radiation hardness comparable to specialized radiation-hardened devices

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

Enhances radiation tolerance by more than 25% through induced trap states in the tunnel oxides, effectively mitigating charge loss from ionizing radiation, as demonstrated by experimental results and simulations.

Implementation Method 1

accelerated aging through controlled program-erase cycling in flash memory to induce trap states in tunnel oxides

Methodology Applied

Scientific EffectTrap states induction:

Implementation Method 2

effectively mitigating charge loss from ionizing radiation

Methodology Applied

Scientific EffectIonizing radiation interaction: Radiation

Implementation Method 3

induce trap states in tunnel oxides, improving ionizing radiation tolerance

Methodology Applied

Scientific EffectCharge trapping:

Data Source

PatentUS11164642B1Systems and methods for hardening flash memory to radiation

Publication Date: 2021.11.02 UNIVERSITY OF ALABAMA

AI summary

A method for radiation hardening flash memory performs accelerated aging on the flash memory by program-erase (PE) cycling the flash memory. Such accelerated aging induces trap states in the tunnel oxide layer of the flash memory, which results in improved ionizing radiation tolerance. The number of cycles used to harden a given memory cell is optimally determined in order to limit effects of the radiation hardening on the reliability of the cell.