Fundamental Aspects of Radiation Event Generation for Electronics and Engineering Research

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Fundamental Aspects of Radiation Event Generation for

Electronics and Engineering Research

Robert A. WellerInstitute for Space and Defense

ElectronicsSchool of EngineeringVanderbilt University

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Overview

• Introduction

• Research Program Background

• Technical Objectives

• Approach

• Expected Research Results

• Technology Transfer

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Introduction

• The Question:1. If you model all the physical processes by which radiation interacts

with materials, and by which electric charge moves in solids, as

accurately as current knowledge permits, can you predict radiation

effects in semiconductor devices from first principles?

2. If not, then why not?

• The essential issue - Complexity!

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Background

• Existing methods for predicting the rate of single event upsets in semiconductor devices have begun to fail because their of their basic assumptions.

• New computational methods developed at Vanderbilt have exposed gaps in basic science that limit our ability to make accurate predictions of single event effects.

• Two important areas needing basic work are:• The generation of final states of ionizing particles following

nuclear reactions.• The microstructure of energy deposition and charge

generation by ions, including the spatial and energy distributions of carriers.

• The detailed motion of charge in matrices of sub 100 nm structures is also important but is not the primary focus of this work.

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SEU Rate for a Modern SRAM

• Comparing a calculation with data from a real SRAM flown by NASA

• Observed Average SEU Rate:• 1x10-9 Events/Bit/Day

• Vendor predicted rate using CREME96:

• 2x10-12 Events/Bit/Day• Classical Method nearly a

factor 500 lower than the observed rate

• VU-ISDE rate:• All relevant physics with Geant4• 1.3x10-10 to 1.3x10-9

Errors/Bit/Day• Wide error bar from Geant4

ion-ion physics uncertainty

Multi-layeredStack

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The Impact of Complexity

NMOS PMOS NMOS

Kevin Warren, VU ISDE

12-T DICE Latch

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A Focus on the Nuclear Physics

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Charge Generation

TiN 0.1 µm

Si 0.25 µmSiO2 0.6 µm

Al 0.45 µm

Al 0.45 µm

SiO2 0.60 µm

Al 0.84 µm

SiO2 1.0 µm

Si-Nitride 0.4 µm

50 µm

SiO2 or W 0.6 µm

TiN 0.1 µm

TiN 0.1 µm

TiN 0.1 µm

TiN 0.1 µm

0

Nuclear Reactions

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Charge Motion

1018 e-/cm3 1014 e-/cm3

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Technical Objectives

• Establish the available data, theory and computation for ion-ion nuclear reactions

• Build virtual experiments that test these models for best fit to semiconductor data

• Identify the best available nuclear reaction codes• Interface and/or adapt the best codes for MRED• Improve the nuclear-physics/charge-transport

interface as necessary for < 100 nm structures• Establish a roadmap for any necessary nuclear

reaction research

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Approach - Strategy

• Identify the best available physics.

• Code the physics (whenever possible) in timeless algorithms.

• Use supercomputer-based high-fidelity simulations to extract the physics that arises from complexity.

• Establish validity by comparison with experimental data.

• Let computer evolution deal with any power shortfall (if possible).

/* int patmat(pattern, string)char *pattern, *string;

patmat() examines the strings 'pattern' and 'string' for equality and returns YES(=1) if they are equal and NO (=0) if not. The string 'pattern' may contain '*'and '?' characters which will match any substring and any single characterrespectively. Either symbol may appear at any location in the pattern. The '*'will also match a NULL string -- that is, the absence of any characters in thedesignated position. The '?' character always requires that there be an explicit(but arbitrary) character present in the test string.

*/

#define YES 1#define NO 0

int patmat(pattern,string)char *pattern, *string; {

register char *p, *s;register int match = NO;p = pattern; s = string;while(*p != '*') {

if(*p != *s && *p != '?')goto retNO;

if(*p++ == '\0') /* Then *s must also. This is a match. */goto retYES;

if(*s++ == '\0') /* No more string, but still some pattern */goto retNO; /* which is not a '*'. No match. */

}if(*++p != '\0') /* '*' at the end matches anything, even a */

while(!patmat(p,s)) /* NULL string. */if(!*s++)

goto retNO;retYES: ++match;retNO: return(match);}

/* Robert A. Weller *//* December, 1990 */

Croc image: http://crocodilian.com/crocfaq/

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Approach - Implementation

• Identify available nuclear reaction models.• Adapt models to mred/Geant4 if necessary.• Develop structures to simulate nuclear

physics and radiation effects experiments.• Conduct simulated experiments for

comparison with experimental data.• Identify the best available models for

practical applications.• Identify essentially-related issues outside

the scope of this effort.

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Manage Complexity with Computing

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Predicting Experiments

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The Structure of MRED

•Python: The common system language.

•MRED: A Python module called mredPy.

•Target: VU Linux cluster.

•Python writes submission scripts, controls job execution, and merges results.

Geant4

MREDC++

SWIG

Python

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Expected Results

• Identify optimum nuclear modes for MRED.• Validate nuclear models against

semiconductor data.• Identify issues related to the interface

between charge generation and transport in sub-100 nm structures.

• Deeper understanding of the intricacies of charge generation.

• Reduced uncertainty in SEU prediction.

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Technology Transfer

• ISDE Engineering

• Collaborative R&D, e.g. NRL/Vanderbilt

• NASA MSFC/Vanderbilt CREME-MC Site

• Major semiconductor supplier relationships

• NASA Center collaborative R&D

• Through students