SINGLE EVENT UPSETS ON STATIC RANDOM
ACCESS MEMORY BY SPENVIS AND PSPICE
SIMULATION AT NEAR EQUATORIAL ORBITS
BY
SOUAAD BEN KARA MAHAMMED
A dissertation submitted in fulfilment of the requirement for
the degree of Master of Science (Electronics Engineering)
Kulliyyah of Engineering
International Islamic University Malaysia
AUGUST 2016
ii
ABSTRACT
Memories, such as Static Random Access Memories (SRAMs) are important parts in
microelectronic circuits. SRAM is used to store data in a circuit. In harsh space
environments with high energetic radiation, SRAM devices are likely to interact with
ionizing electrons, protons and various ions. This interaction induces excess charge
within the device that modifies its electronic state, causing various types of unwanted
effects including Single Event Upset (SEU). This work computes the critical charge
(Qcrit) that is required to upset 90nm and 180nm CMOS 6T SRAM cells at their two
most sensitive nodes at Q and Qbar. Different current values are used with a supplied
voltage ranging from 0.2 V to 1V. Based on the obtained critical charge, the single
event upset rates are reported as a function of radiation particles, shielding and
striking nodes (transistor drain) size. This investigation is performed by simulation
devices in Near Equatorial Orbit (NEqO) environment, using ORCAD PSPICE and
SPENVIS simulation tools. The results show that Q node is more vulnerable to SEU
than Q bar node for both technologies similarly. 90nm SRAM is more susceptible to
SEU than 180nm. It is also found that shielding by 0.5 mg/cm2 Al has no effect on
Galactic Cosmic Rays(GCR) radiation. Solar particles (SP) dominates the effect rates,
however trapped particles (TP) have the least effects. Drainlength plays an important
role in the SEU rates variation. It may minimize the upset rates with small drain length
and low supplied voltage. Shielding by 0.5 g/cm2 of Al and decreasing the drain
length can mitigate the transistor susceptibility to SEU. Thus, it can be justified that
smaller CMOS transistor technology has high potential to be used in space.
iii
خلاصة البحثABSTRACT IN ARABIC
تشكل جزءا هاما في الدارات الميكروالكترونية ( SRAMs) ذاكرة الوصول العشوائي الثابتةخلايا الذاكرة ، كــ اجهزة الذاكرة الحديثة. في الفضاء، بوجود محيط قاس بسبب النشاط الإشعاعي العالي، فانه من الممكن أن تتفاعل
SRAM مع الإلكترونات والبروتونات المؤينة و مختلف الأيوناتالاخرى. هذا التفاعل يحث على انتاج فائض فيالشحنة داخل الجهاز والذي يؤدي الى تغيير حالته الالكترونية مما يسبب أنواع مختلفة من الآثار المزعجة على غرار
( المطلوبة لاضطراب كل من Qcritالحرجة )هذا العمل يحسب كمية الشحنة (.SEU)حادثة أحادي الاضطراب عقدتين الأكثر عند ال 90nm CMOS 6Tو SRAM :180 nm CMOS 6Tخلايا الذاكرة
على قيم الشحنة ا. وبناء1Vإلى V 0.2مورد بتغير من تيار حساسية لديهما. قيم مختلفة للتيار قد استعملت مع الجسيمات الإشعاعية ، التغليف قد تم تقريرها وبدلالة SEUلـــ ( التي تم الحصول عليها، معدلات اQcritالحرجة )
(، وبتتطبيق NEqOوحجم العقدة المصدومة. هذا البحث تم تنفيذه في محيط المدارات الاستوائية الدنى )PSPICE ORCAD وأدوات المحاكيSPENVIS وقد أظهرت النتائج أن في كلا التكنولوجيا العقدة .Q
3.5من الالمنيوم يستطيع أن يمنع نحو mg/cm 2 0.5التغليف بـ . Qbarمن العقدة SEUهي أكثر عرضة للـ 3x 10 من معدلات الــSEU من ناحية أخرى، ليس له أي تأثير على أشعة الـ .GCR مما يعني أن نفس ،
( على حدوث تأثيرالـ SPشمسية )تم الحصول عليها عن قبل وبعد تغطية. تهيمن الجسيمات ال SEUمعدلات الـ SEU( ولكن الجزيئات المحاصرة ،TP أقل تأثير. طول العقدة يلعب دورا هاما في تغيير معدلات الـ )SEU فيمكن.
إلى النصف إذا أخذ الطول المناسب قي التوتر المنخفض.بالإضافة إلى ذلك، فإن التغليفبـ SEUالتقليل من معدلات الــ 20.5 mg/cm يمكن من التخفيف من حساسية الترانزستورللـ سرب يرفي طول الموالتصغSEU وهكذا،تكنولوجيا
النانومتر لديها امكانات عالية لاستخدامها في الفضاء.CMOSالترانزستور
iv
APPROVAL PAGE
I certify that I have supervised and read this study and that in my opinion, it conforms
to acceptable standards of scholarly presentation and is fully adequate, in scope and
quality, as a thesis for the degree of Master of Science (Electronics Engineering).
…………………………………..
Nurul Fadzlin Hasbullah
Supervisor
…………………………………..
Rosminazuin Bt. Ab. Rahim
Co-Supervisor
I certify that I have read this study and that in my opinion it conforms to acceptable
standards of scholarly presentation and is fully adequate, in scope and quality, as a
thesis for the degree of Master of Science (Electronics Engineering).
…………………………………..
Sheroz Khan
Internal Examiner
…………………………………..
A. H. M. Zahirul Alam
Internal Examiner
This dissertation was submitted to the Department of Electrical and Computer
Engineering and is accepted as a fulfilment of the requirement for the degree of
Master of Science (Electronics Engineering).
…………………………………..
Teddy Surya Gunawan
Head, Department of Electrical
and Computer Engineering
This dissertation was submitted to the Kulliyyah of Engineering and is accepted as a
fulfilment of the requirement for the degree of Master of Science (Electronics
Engineering).
…………………………………..
Md. Noor Hj. Salleh
Dean, Kulliyyah of Engineering
v
DECLARATION
I hereby declare that this dissertation is the result of my own investigations, except
where otherwise stated. I also declare that it has not been previously or concurrently
submitted as a whole for any other degrees at IIUM or other institutions.
Souaad Ben Kara Mahammed
Signature ........................................................... Date .........................................
vi
COPYRIGHT PAGE
INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA
DECLARATION OF COPYRIGHT AND AFFIRMATION OF
FAIR USE OF UNPUBLISHED RESEARCH
SINGLE EVENT UPSETS ON STATIC RANDOM ACCESS
MEMORY BY SPENVIS AND PSPICE SIMULATION AT NEAR
EQUATORIAL ORBITS
I declare that the copyright holders of this dissertation are jointly owned by the student
and IIUM.
Copyright © 2016 Souaad Ben Kara Mahammed and International Islamic University Malaysia. All
rights reserved.
No part of this unpublished research may be reproduced, stored in a retrieval system,
or transmitted, in any form or by any means, electronic, mechanical, photocopying,
recording or otherwise without prior written permission of the copyright holder
except as provided below
1. Any material contained in or derived from this unpublished research may
be used by others in their writing with due acknowledgement.
2. IIUM or its library will have the right to make and transmit copies (print
or electronic) for institutional and academic purposes.
3. The IIUM library will have the right to make, store in a retrieved system
and supply copies of this unpublished research if requested by other
universities and research libraries.
By signing this form, I acknowledged that I have read and understand theIIUM
Intellectual Property Right and Commercialization policy.
Affirmed by Souaad Ben Kara Mahammed
Signature ……..…………………….. Date ………………………..
vii
ACKNOWLEDGEMENTS
All praise to ALLAH the almighty for giving me the strength, patience and ability to
complete this research. This research would have not been possible without His
guidance.
Words cannot express how thankful I am to my supervisor, Assoc. Prof, Nurul Fadzlin
for her kindness, understanding, support and deep guidance throughout my research.
My gratefulness also goes to my co-supervisor, Dr. Rosmina
Zuin and Mr. Sharizal Fadlie. Thanks to Dr. Mohamed Mahmoud Ibrahim for all the
help, support and immense knowledge he gave me. And to everyone that provided me
with any kind of help and support.
A deep hearted gratitude goes to my parents who supported me with every possible
way. They gave me more than I deserve, all over my life. Also I acknowledge the
financial and moral support of my brothers and sisters and in particular Khaled and
Nadjima. Deep thanks to my beloved family may Allah bless them and reward them in
this world and the hereafter.
I would like to express my sincere gratitude to all my friends for their encouragement,
moral support and guidance throughout this journey.
Thanks to everyone who remembered me in their Dua.
viii
TABLE OF CONTENTS
Abstract ................................................................................................................... ii Abstract in Arabic .................................................................................................. iii Approval page ........................................................................................................ iv
Declaration .............................................................................................................. v Copyright Page ....................................................................................................... vi Acknowledgments .................................................................................................. vii Table of Contents ................................................................................................... viii List of Tables .......................................................................................................... x
List of Figures ......................................................................................................... xi
List of Abbreviations ............................................................................................. xiii
List of Symbols ....................................................................................................... xi
CHAPTER ONE: INTRODUCTION .................................................................. 1 1.1 Background of The Study ....................................................................... 1
1.2 Problem Statement and Its Significance ................................................. 3 1.3 Research Scope ....................................................................................... 4
1.4 Research Objectives................................................................................ 4 1.5 Research Methodology ........................................................................... 5 1.6 Thesis Outlines ....................................................................................... 6
CHAPTER TWO: LITERATURE REVIEW ..................................................... 8 2.1 Overview................................................................................................. 8 2.2 Space Radiation Environment ................................................................ 10
2.2.1 Galactic Cosmic Rays (GCR) ....................................................... 10 2.2.2 Solar Particle Events (SPE)........................................................... 11
2.2.3 Trapped Particles (TP) .................................................................. 12 2.3 Single Event Upset (Seu) ........................................................................ 14
2.4 Direct and Indirect Ionization ................................................................. 15 2.4.1 Direct Ionization ........................................................................... 16 2.4.2 Indirect Ionization ......................................................................... 17
2.5 Static Random Access Memory (6t Cells).............................................. 17
2.6 Single Event Upset in 6t-Sram ............................................................... 18 2.7 The Critical Charge for SEU Inducement .............................................. 21 2.8 Previous Works ....................................................................................... 22
2.8.1 Radiation and SEUs ...................................................................... 22 2.8.2 Research on Distinct Orbits .......................................................... 24 2.8.3 Examples of Launched Satellites and Their Missions .................. 25 2.8.4 Examples of Launched Satellites and Their Missions .................. 26 2.8.5 The SEU in SRAM 6T Cells ......................................................... 27
2.8.6 Benchmarking Papers ................................................................... 28 2.9 Summary ................................................................................................. 30
CHAPTER THREE: METHODOLOGY ............................................................ 32 3.1 Overview................................................................................................. 32
ix
3.2 Simulation Details .................................................................................. 32 3.3 Pspice Simulation and Critical Charge Modelling ................................. 33
3.3.1 The 6T CMOS SRAM Cell Function ........................................... 34
3.3.1.1 Standby State .................................................................... 35 3.3.1.2 Reading State .................................................................... 35 3.3.1.3 Writing State ..................................................................... 36
3.3.2 Current Pulse Description For Simulated Circuit ......................... 37 3.4 Spenvis Models and Simulation ............................................................. 39
3.4.1 SPENVIS Coordinate Generator ................................................... 40 3.4.2 SPENVIS Radiation Models ......................................................... 41
3.4.2.1 Trapped Particles Model (AP8/AE8) ............................... 42 3.4.2.2 Solar Event Particules Model (CRÈME-96) .................... 43
3.4.2.3 Galactic Cosmic Rays Model (ISO 15390) ...................... 44 3.4.3 Short Term SEU Rates Models ..................................................... 44
3.4.3.1 The SEU Rates Induced by Direct Ionisation ................... 46
3.4.3.2 Soft Upset Rates Estimation Methods .............................. 47 3.5 Summary ................................................................................................. 48
CHAPTER FOUR: CRITICAL CHARGE (Qcrit) MODELLING and SINGLE
EVENT UPSET (SEU) RATES SIMULATION…………49
4.1 Overview................................................................................................. 49
4.2 Pspice Simulation ................................................................................... 49 4.2.1 The 6T-SRAM Cell Circuit before Radiation ............................... 49 4.2.2 6T SRAM Cell with Current Source Injection (After
Radiation) ..................................................................................... 52 4.3 SPENVIS Simulation ............................................................................. 58
4.3.1 Radiation Sources ......................................................................... 58 4.3.1.1 Trapped Protons and Electrons ......................................... 58
4.3.1.2 Reading State .................................................................... 60 4.3.1.3 Galactic Cosmic Rays (GCR) Ions ................................... 60
4.3.2 Single Event Upset Rates .............................................................. 61
4.3.2.1 Orbital Radiation Effects on SEU .................................... 61
4.3.2.2 Scaling Effects on SEU Rates .......................................... 65 4.3.2.3 Radiation Particules Type Effets on SEU ......................... 67 4.3.2.4 Drain Size Effects on SEU ............................................... 73
4.4 Summary ................................................................................................. 77
CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS .............. 78 5.1 Conclusions ............................................................................................ 78
5.2 Contribution ............................................................................................ 79 5.3 Limitations and Future Recommendations ............................................. 79
REFERENCES ....................................................................................................... 81
Appendix I ............................................................................................................... 81
Appendix II .............................................................................................................. 81
Appendix III ............................................................................................................. 90
Appendix IV ............................................................................................................. 92
x
LIST OF TABLES
Table No. Page No.
Table 1.1 Satellites classification. 1
Table 1.2 Earth orbits types and altitudes 2
Table 2.1 Summary of relevant literatures of SEU and radiation simulation 29
Table 3.1 Summary of relevant literatures of SEU and radiation simulation 40
Table 4.1 Summary of relevant literatures of SEU and radiation simulation 51
xi
LIST OF FIGURES
Figure No. Page No.
Figure1.1Flow Chart of Research Methodology 6
Figure 2.1The Earth’s Magnetosphere 8
Figure 2.2Van Allen radiation belts with two probes satellites flying through them 12
Figure 2.3Heavy ions and protons striking 15
Figure 2.4Transistor Memory Cell (6T Cell) 17
Figure 2.5An SEU in a memory cell due to a pulse strike 18
Figure 2.6Drain voltage waveforms for no upset, upset and in the upset threshold 19
Figure 2.7Sensitive areas and SEUs in a 6T-SRAM cell circuit 19
Figure 2.8Qcrit vs. cell supply voltage for particle strikes at off-NMOS/PMO 20
Figure 3.1Diagram of critical charge modeling by means of PSPICE 32
Figure 3.2Six-transistor (6T) CMOS SRAM cell 33
Figure 3.36T CMOS SRAM cell during a read operation 34
Figure 3.4The 6T CMOS SRAM cell during a write operation 35
Figure 3.5The current pulse sources and collection (a) the particle track
(b) The charge drift (c) the charge diffusion (d) the pulse curve 37
Figure 3.6The procedure for SEU rates calculation in SPENVIS 38
Figure 3.7 The three steps taken to define Razaksat coordinates 40
Figure 3.8The used trapped radiation models 41
Figure 3.9The used solar particle flux model 42
Figure 3.10The used Galactic Cosmic Rays Model 43
Figure 3.11Single Event Upsets model input parameters in SPENVIS 45
Figure 3.12Sensitive node shape and dimensions 46
xii
Figure 4.1Modelling of 6T SRAM cell in ORCAD PSPICE 50
Figure 4.2The voltages in the cell (a) at bit line (BL) and bit line bar (BLB)
(b) cell at Q (VQ) and Qbar (VQbar) nodes 51
Figure 4.3Current injection at Q node in 6T-SRAM cell circuit 53
Figure 4.4Current injection at Qbar node in 6T-SRAM cell circuit 54
Figure 4.5(a) The injected current waveform (Iexp, I2= 0.47mA). (b) The inverters
output voltages with no upset occurrence at Q node(c)The inverters output
voltages with upset occurrence at Q node 55
Figure 4.6 The critical charge as a function of cell supplied voltage at Q and Qbar
nodes for (a) 90nm circuit. (b) 180nm circuit 57
Figure 4.7The critical charge as a function of current injected resulted from particle
strikes at Q and Qbar node for (a) 90nm circuit. (b) 180nm circuit 58
Figure 4.8The average integral and differential fluxes of (a) Trapped protons
(b) Trapped electrons for 3 years mission at Razaksat orbit 60
Figure 4.9Solar proton flux spectra (peak 5-minute-averaged fluxes) 61
Figure 4.10GCR ions flux spectra 62
Figure 4.1Direct ionization SEUs rates concerning Razaksat through its lifetime
mission for 90nm SRAM (a) Unshielded Q node. (b) Shielded Q node 64
Figure 4.12Direct ionization SEUs rates concerning Razaksat through its lifetime
mission for 180nm SRAM (a) Unshielded Q node. (b) Shielded Q node 66
Figure 4.13SEU rates for shielded and unshielded 6T-SRAM cell concerning 90nm
and 180nm technologies at NEqO regarding (a) Q node (b) Qbar node 67
Figure 4.14SEU rates for 90nm Qnode 6T SRAM cell (a) shielded ,(b) unshielded 69
Figure 4.15SEUrates for 90nm Qbar node 6Tsram cell (a) shielded,(b) unshielded 71
Figure 4.16SEU rates for 180nm Qnode 6T SRAM cell (a) shielded , (b) unshielded 73
Figure 4.17SEU rates for 180nm Qbar node 6Tsram cell (a) shielded,(b) unshielded 74
Figure 4.18SEU rates versus drain length in 90nm cell at (a) Q node (b) Qbar node 76
Figure 4.19SEU rates versus drain length in 180nm cell at (a) Q node (b) Qbar node 78
xiii
LIST OF ABBREVIATIONS
6T SRAM Six Transistors Static Random Access Memory
Al Aluminum
BL Bit line
BLB Bit line bar
CMEs Coronal Mass Ejections
CMOS Complementary metal-oxide-semiconductor
ESA Space situational awareness
GaAs Gallium Arsenide
GCR Galactic cosmic rays
GEO Geostationary Earth Orbit
IRPP Integral rectangular parallelepiped
LEO Low Earth Orbit
LET Linear Energy Transfer
MCU Multiple Call Upset
NEqO NEar Equatorial Orbit
NMOS N-type metal-oxide-semiconductor
PMOS P-type metal-oxide-semiconductor
RPP Rectangular Parallelepiped
SAA South Atlantic Anomaly
SEB Single Event Burnout
SEE Single Event Effect
SEGR Single Event Gate Rapture
xiv
SEL Single Event Latch-up
Si Silicone
SP Solar Particles / Protons
SPE Solar Particle Events
SPENVIS Space Environment Information System
SWE Space Weather
TID Total Ionization Dose
TP Trapped Particles / Protons
xv
LIST OF SYMBOLS
A Ampere
GeV Gaga electro-volt
Icoll Collected current
Iexp Exponential current
Iinj Injected current
KeV Kilo electro-volt
MeV Mega electro- volt
mg/cm2 Milligram per centigram square
nm Nanometer
pfu Particle flux unit
Qcoll Collected charge
Qcrit Critical charge
Td Rise delay
Tf Fall delay
Vdd Supply voltage
τf Fall time
τr Rise time
1
CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
In this age, the fields of science, technology and the utilisation of computer
applications have become an important aspect in the development of nations. In that
Space technology is playing an increasingly important role in most space exploration
by modern societies. In particular, since the launching of the first artificial earth
satellite, known as Sputnik1, by the former Soviet union 58 years ago, this technology
has been under goingrapid development throughout the world. By December 2013,
sixty one (61) countries have successively launched their own satellites.
Nowadays, thousands of satellites are orbiting the Earth, providing services in
different fields including astronomy, communication, earth observation, military,
navigation, weather forecasting, scientific research and space stations. Satellites are
usually classified based on their mass (Farre Ponsa, 2012) as in Table 1.1.
Table 1.1 Satellites classification.
Satellite mass Satellite class
500 kg and above
100 – 500 kg
10 – 100 kg
1 – 10 kg
0.1 – 1 kg
Below 0.1 kg
Common satellite
Minisatellite
Microsatellite
Nanosatellite
Picosatellite
Femtosatellite
2
This has motivated scientists to design more advanced satellites, that have low
cost, low weight and low power consumption. For instance, a built prototype of a
femtosatellite type costs only $300 (Barnhart et al. 2009). Smaller satellites such as
AttoSatellites and ZeptoSatellites are aimed to be built with just a few dollars per unit
prototype (Tahri et al., 2013). Each spacecraft or satellite is designed based on its
objectives and working environment. This latter depends on the targeted orbit which
has to be accurately defined.
Basically, Earth has three types of orbits:
Low Earth Orbit (LEO): It has an altitude between 160 km and 2000 km, most
scientific and all manned satellites are placed in LEO.
Medium Earth Orbit (MEO): Acquires the height between 2000 and 35786 km,
below the geosynchronous orbit. The most prevalent use of satellites in this
orbit type is navigation, communication, space environment science and a
particular region supervision.
Geostationary Earth Orbit (GEO) is 35,786 km high up the Earth’s equator. A
geostationary satellite has a circular rotation pursuing the Earth’s movement
direction. A ground observer views the geostationary satellite as a motionless
object. It is worth highlighting that weather and communication satellites are
predominantly positioned in geostationary orbits. Table 1.2 summarizes the
attitude ranges of the three types of orbits ( Suparta & Zulkeple, 2014).
Table 1.2 Earth orbits types and altitudes
Low Earth Orbit
(LEO)
Middle Earth Orbit
(MEO)
Geostationary Earth Orbit
(GEO)
400 km
685 km
19,100 km
20,200 km
35,793 km
1000,000 km
3
Designing, building and launching a satellite is a time consuming process that
requires high budget. Therefore, its failure while in the space can cost hundreds of
millions dollars. Some of the hazardous elements in the space medium that can
damage a satellite include the radiation beltsaround the Earth, solar emissions, cosmic
rays, magnetic fields, plasma environments and space debris. As hardware technology
is advancing in capability, size of the electronic components is obviously shrinking
and satellites susceptibility to radiation impacts such as radiation damage, single event
impact (SEU) and charging is increasing (Baker, 2000). Therefore, when a space
mission is planned, a thorough investigation on the space environment and its
influence on the spacecraft’s microelectronics and astronaut’s safety has to be
conducted before launching.
In addition, investigating radiation problem mitigation through experimental
researches is considerably expensive and can cause undesirable side effects in
energetic radiation environment. The availability of advanced computer software and
simulation tools such as CREME96 (Tylka et al, 1997) and SPENVIS (Heynderickx et
al., 2004), which providing a gentle and inexpensive research tools can ensure the
device functionality and potentially saving money.
1.2 PROBLEM STATEMENT AND ITS SIGNIFICANCE
Highly ionizing cosmic rays and solar particles form a harsh radiation environment in
space they are found to be detrimental to spacecraft materials and devices. Several
radiation effects occur because of radiation environment. For instance, Single Event
Upset (SEU), a type of these effects as it is considered as a soft error, has a negative
effect on the spacecraft Static Random Access Memories (SRAMs). Moreover,
shrinking of transistor channel’s length in spacecraft devices will inevitably cause
4
effects such as SEU due to reduction in the critical charge. A spacecraft susceptibility
to SEU depends largely on their orbit, because each orbit has different radiation
levels. Near Equatorial Orbits (NEqO) are LEO orbits are categorized as a critical
orbit due to its maximum peak overpasses per day. High radiation levels are of much
interest to countries near to the equator such as Malaysia (RazakSAT) and Singapore
(TELEOS1).
Experimental analysis of the SEU problem is considerably expensive and
known to have undesirable side effects due to the emitted energetic radiation. The
availability of advanced and accurate computer software and simulation codes provide
safe and inexpensive research tools that can ensure reliable analysis of the device
functionality. It is envisioned that the finding of this project will have a major
importance in reliability enhancement and lifespan prolongation of RazakSAT, as
well as likewise the future of satellite generations.
1.3 RESEARCH SCOPE
This study explores and computes the natural cosmic radiation at Near Equatorial
Orbit (the orbit hovered by RasakSAT, Malaysian satellite) and investigates its SEU
effect on 6T SRAM, using two types of modeling software; SPENVIS and PSPICE.
1.4 RESEARCH OBJECTIVES
Based on the problem statement, the main goal of this research is to explore the SEUs
rates on 6T SRAM at Near Equatorial Orbit for RazakSAT. This goal can be allocated
as the following objectives:
5
1- To model 6T SRAM cell using PSPICE and to estimate the critical charge
variation for 90nm and 180nm CMOS technologies variability of
transistors models, injected with current and supplied voltage.
To analyze the critical charge effect obtained from PSPICE simulation on the SEU
rates at NEqO orbit (RazakSAT orbit) on specific sensitive volume using SPENVIS.
1.5 RESEARCH METHODOLOGY
The applied methodology to achieve the stated objectives is as follows in these
sequential steps:
1) Data collection of the needed information with critical analysis from previous
studies on SEUs and mechanism
2) Identify the key parameters adopted of the model.
3) Study the radiation environment with different particles, its energies, and
fluxes at near equatorial orbit.
4) Modelling the 6T SRAM behaviors of 6T SRAM with and without SEU.
5) Extract the critical charge as a function of supplied voltage, injected current
and CMOS transistor parameters using PSPICE software.
6) Extract the SEU rates correlated to the particle energy and critical charge,
based on data generated from previous simulation applying SPENVIS models.
7) Analyze, compare and report the outputs of the two models for SRAM
applications in equatorial environment.
The research methodology adopted for achieving the stated objectives is depicted in
Figure 1.1.
6
Figure 1.1The flow chart of the methodology
1.6 THESIS OUTLINES
In addition to an introduction, scope and objectives given in the first chapter; this
thesis comprises of four more chapters, which present an overview on space radiation
7
and a specific study regarding SEUs in 6T SRAM devices in the Near Equatorial
Orbit.
The second chapter is devoted to literature review; the properties specificat
space environment are given. In addition, the single event upset definition and
mechanism are explored.
The third chapter is dedicated to the methodology followed and the software
used in order extract details and statistics. The two mainly software used are:
SPENVIS for radiation modulation and PSPICE for circuit simulation and critical
charge calculation.
The fourth chapter provides results of the study and discusses the finding.
Here, the attained results are examined and compared with those from contemporary
findings on the subject.
Conclusions and further work suggestions are presented in the fifth chapter.
8
CHAPTER TWO
LITERATURE REVIEW
2.1 OVERVIEW
What lies beyond the Earth’s atmosphere is not a vast and vacant space. There are
significant levels of radiation particles consisting mostly of protons, electrons and
heavy ions. Certain regions have been detected to contain varying levels of particles
which exert slightly different effects on electronic devices. Also, the earth possesses a
magnetic field, called the magnetosphere (see Figure 2.1). In the case of a satellite
orbiting Earth, coming into contact with this magnetosphere means being exposed to
different types of radiation which may affect its functions.
Figure 2.1The Earth’s Magnetosphere (Space Environments and Effects
Program, 2015).
The shape of the magnetosphere depends on varying forms of solar activity as part of
the Sun’s 11-year cycle. In the event of solar storms or other solar events, the
9
magnetosphere is compressed which permits outside radiation particles to penetrate
into the magnetosphere and become trapped within.
Radiation exposure can cause significant damage to microelectronic circuits
and devices. This kind of damage can be categorized as Total ionizing dose (TID) and
single event effects (SEE). A TID is having a cumulative degradation of a device after
it has been exposed to ionizing radiation over a certain period of time. The second
most common type of damage known to be caused by the interaction of
semiconductor material and high-energy ionizing radiation is the so-called single
event effect (SEE). A SEE can be defined as an electrical disturbance occurring in a
semi-conductive microelectronic circuit caused by the passage of a single ionizing
high-energy space born particle (accelerator). When a single ionizing high-energy
particle penetrates into an electrical circuit, it leaves behind a dense plasma track in
the form of electron-hole pairs. Such a passage can cause a circuit error or even circuit
failure if a sufficiently high plasma charge is collected from the plasma track at a
sensitive node in the circuit.
The different types of SEEs can be classified into three most important and
frequent effects, listed as follows:
Single-event upset (SEU): a change of state or transient state induced by an
ionizing particle entering a device. The ionizing particle can be a cosmic ray or
a proton. This type of SEE can occur in digital, analog, and optical
components or in the surrounding circuitry.
Single-event latch up (SEL): a potentially destructive condition involving
parasitic circuit elements. If the increased current exceeds the device’s
maximum specification, it can destroy it if no safety measures are put in place
to limit the maximum current strength.
