Iec 62396-1-2016.Pdf

IEC 62396 1 Edition 2 0 201 6 01 INTERNATIONAL STANDARD Process management for avionics – Atmospheric radiation effects – Part 1 Accommodation of atmospheric radiation effects via single event effects[.]

IEC 62396- 1

Editio 2.0 2 16-01

Process management for avionics – At mospheric radiat ion efect s –

Part 1: Accommodat ion ofat mospheric radiat ion efect s via single event efect s

w it hin avionics elect ronic equipment

THIS PUBLICATION IS COPYRIGHT PROTECTED

Copyr ight © 2 16 IEC, Ge e a, Switzer la d

Al rig ts r es r ve Unle s oth rwis s e ifi d, n p rt of this p blc tio ma b r epr od c d or uti z d in a y form

or b a y me n , ele tr onic or me h nic l in lu in p oto o yin a d microfim, with ut p rmis io in wr itin from

eith r IEC or IEC's memb r Natio al Commite in th c u tr y of th re u ste If y u h v a y q e tio s a o t IEC

c p r i ht or h v a e q ir y a o t o tainin a ditio al ri hts to this p blc tio , ple s c nta t th a dr es b low or

y ur lo al IEC memb r Natio al Commite for ur th r informatio

Th Intern tio al Ele trote h ic l Commis io (IEC) is th le din glo al org niz tio th t pr ep res a d p bls e

Internatio al Sta d r ds for al ele tri al ele tr onic a d relate te h olo ie

Abo t IEC p blc tio s

Th te h ic l c nte t of IEC p blc tio s is k pt u d r c n ta t r eview b th IEC Ple s ma e s re th t y u h v th

late t e itio ,a c rr ig n a or a ame dme t mig t h v b e p bls e

IEC Cat alo ue - webst ore.e ch/ cat alo ue

Th st an -alo e a plc t io for c n ultin th e tire

biblo ra hic l informat io o IEC Intern tio al Sta d rd ,

Te h ic l Sp cific tio s, Te h ic l R ep rts a d oth r

d c me ts A v aia le for P , Ma OS, A ndroid Ta let s a d

iPa

IEC p blc t i ns s arch - www ie ch/ se rch u

Th a v an e s arc e a le t o fin IEC p blc t io s b a

variety of crit eria (efere c n mb r, t ext, t ec nic l

c mmitt e,…) It als gives informatio o projec t s, re la e

a d wit hdrawn p blc tio s

IEC Just P blshed - webst ore.e ch/ just pu lshed

St ay u to d te o al n w IEC p blc tio s Ju t Pu ls e

d t ais al n w p blc t io s rele s d A v aia le o ln a d

als o c a mo t h b emai

Ele t ro edia - www ele t ro edia.org

Th world's le din o ln dic t io ary of elec t ro ic a d

ele t ric l terms c nt ainin 2 0 0 terms a d d finitio s in

En ls a d Fre c , wit h e uiv ale t t erms in 15 a dit io al

la g a e Als k nown a t he Intern t io al Ele trote h ic l

Vo a ulary (IEV ) o ln

IEC Glos ar y - st d.e ch/ glos ary

6 0 0 elec t rot ec nic l t ermin lo y e t rie in En ls a d

Fre c e t ra te fom t he Terms a d Definitio s cla s of

IEC p blc tio s is u d sin e 2 0 Some e t rie h v e b e

c ole te fo m e rler p blc t io s of IEC TC 3 , 7 , 8 a d

CISPR

IEC Cust omer Servic Cent re - webst ore.ec ch/ csc

If y ou wis to giv e u your fe d a k o t his p blc tio or

n e furt her a sista c , ple s c nta t t he Cu tomer Serv ic

Ce t re:c c@ie c

IEC 62396- 1

Edit io 2.0 2 16-01

Process management for avionics – At mospheric radiat ion efect s –

Part 1: Accommodat ion of at mospheric radiat ion efect s via single event efect s

w it hin avionics elect ronic equipment

INT ERNAT IONAL

ELECT ROT ECHNICAL

FOREWORD 6

INTRODUCTION 8

1 Sco e 9

2 Normative ref eren es 9

3 Terms an def i ition 9

4 Ab reviation an acron ms 18 5 Radiation en ironment of the atmosphere 21

5.1 Radiation generation 21

5.2 Ef fect of secon ary p rticles on avionic 21

5.3 Atmospheric neutron 21

5.3.1 General 21

5.3.2 Atmospheric neutron energ sp ctrum an SEE cros -section 2

5.3.3 Altitu e variation of atmospheric neutron 2

5.3.4 L titu e variation of atmospheric neutron 2

5.3.5 Thermal neutron within aircraf t 2

5.4 Secon ary proton 2

5.5 Other p rticles 2

5.6 Solar en an ements 2

5.7 Hig altitu es gre ter than 60 0 0 f t (18 2 0 m) 2

6 Ef fects of atmospheric radiation on avionic 3

6.1 Typ s of radiation eff ects 3

6.2 Sin le event eff ects (SEEs) 3

6.2.1 General 3

6.2.2 Sin le event upset (SEU) 31

6.2.3 Multiple bit upset (MBU) an multiple cel upset (MCU) 31

6.2.4 Sin le ef fect tran ients (SETs) 3

6.2.5 Sin le event latc -up (SEL) 3

6.2.6 Sin le event fu ctional inter upt (SEFI) 3

6.2.7 Sin le event burnout (SEB) 3

6.2.8 Sin le event gate rupture (SEGR) 3

6.2.9 Sin le event in u ed hard er or (SHE) 3

6.2.10 SEE p tential ris s b sed on future tec nolog 3

6.3 Total ionisin dose (TID) 3

6.4 Displacement damage 3

7 Guidan e f or s stem desig s 3

7.1 Overview 3

7.2 Sy tem desig 4

7.3 Hardware con ideration 41

7.4 Electronic devices c aracterisation an control 4

7.4.1 Rigour an dis ipl ne 4

7.4.2 L vel A s stems 4

7.4.3 L vel B 4

7.4.4 L vel C 4

7.4.5 L vels D an E 4

8 Determination of avionic sin le event ef fects rates 4

8.1 Main sin le event ef fects 4

8.2 Sin le event eff ects with lower event rates 4

8.2.1 Sin le event burnout (SEB) an sin le event gate rupture (SEGR) 4

8.2.2 Sin le event tran ient (SET) 4

8.2.3 Sin le event hard er or (SHE) 4

8.2.4 Sin le event latc -up (SEL) 4

8.3 Sin le event eff ects with hig er event rates – Sin le event upset data 4

8.3.1 General 4

8.3.2 SEU cros -section 4

8.3.3 Proton an neutron b ams f or me s rin SEU cros -section 4

8.3.4 SEU p r bit cros -section tren s in SRAMs 5

8.3.5 SEU p r bit cros -section tren s an other SEE in DRAMs 51

8.4 Calc latin SEE rates in avionic 5

8.5 Calc lation of avaia i ty of ul red n an y 5

8.5.1 General 5

8.5.2 SEU with mitigation an SET 5

8.5.3 Firm er ors an f aults 5

9 Con ideration for SEE compl an e 5

9.1 Compl an e 5

9.2 Confirm the radiation en ironment for the avionic a pl cation 5

9.3 Identify the s stem develo ment as uran e level 5

9.4 As es prelminary electronic eq ipment desig for SEE 5

9.4.1 Identify SEE-sen itive electronic comp nents 5

9.4.2 Quantify SEE rates 5

9.5 Verify that the s stem develo ment as uran e level req irements are met for SEE 5

9.5.1 Combine SEE rates for the entire s stem 5

9.5.2 Management of electronic comp nents control an de en a i ty 5

9.6 Cor ective action 5

An ex A (informative) Thermal neutron as es ment 5

An ex B (informative) Method for calc latin SEE rates in avionic electronic 5

B.1 Pro osed in-the-lo p s stem test – Ir adiatin avionic LRU in neutron/proton b am, with output fed into aircraf t simulation computer 5

B.2 Ir adiatin avionic LRU in a neutron/proton b am 5

B.3 Uti sin existin SEE data f or sp cific electronic comp nents on LRU 5

B.3.1 Neutron proton data 5

B.3.2 He v ion data 6

B.4 Ap lyin generic SEE data to al electronic comp nents on LRU 61

B.5 Comp nent level laser simulation of sin le event ef fects 6

B.6 Determination of SEU rate f om service monitorin 6

An ex C (inf ormative) Review of test faci ty avai a i ty 6

C.1 F ci ties in the USA an Canada 6

C.1.1 Neutron faci ties 6

C.1.2 Proton f aci ties 6

C.1.3 L ser f aci ties 6

C.2 F ci ties in Euro e 6

C.2.1 Neutron faci ties 6

C.2.2 Proton f aci ties 71

C.2.3 L ser f aci ties 7

An ex D (informative) Ta ular des ription of variation of atmospheric neutron flu

with altitu e an latitu e 7

An ex E (informative) Con ideration of eff ects at hig er altitu es 7

An ex F (informative) Prediction of SEE rates f or ion 8

An ex G (inf ormative) L te news as of 2 14 on SEE cros -section a plca le to the atmospheric neutron en ironment 8

G.1 SEE cros -section key to SEE rate calc lation 8

G.2 Limitation in compi n SEE cros -section data 8

G.3 Cros -section me s rements (fig res with data fom publc l terature) 8

G.4 Con ervative estimates of SEE cros -section data 8

G.4.1 General 8

G.4.2 Sin le event upset (SEU) 8

G.4.3 Multiple cel upset (MCU) 8

G.4.4 Sin le event fu ctional inter upt (SEFI) 8

G.4.5 Sin le event latc -up (SEL) 8

G.4.6 Sin le event tran ient (SET) 91

G.4.7 Sin le event burnout (SEB) 9

An ex H (inf ormative) Calc latin SEE rates f rom non-white (non-atmospheric l ke) neutron cros -section for smal ge metry electronic comp nents 9

H.1 Energ thres old 9

H.2 Nominal neutron flu es 9

H.3 Calc latin event rates u in non-atmospheric lke cros -section for smal ge metry electronic devices 9

Biblogra h 9

Fig re 1 – Energy sp ctrum of atmospheric neutron at 4 0 0 ft (12 16 m), latitu e 4 ° 2

Fig re 2 – Model of the atmospheric neutron flu variation with altitu e (se An ex D) 2

Fig re 3 – Distribution of vertical rigidity c t-off s arou d the world 2

Fig re 4 – Model of atmospheric neutron flu variation with latitu e 2

Fig re 5 – Energy sp ctrum of proton within the atmosphere 2

Fig re 6 – Sy tem safety as es ment proces 3

Fig re 7 – SEE in relation to s stem an LRU eff ect 4

Fig re 8 – Variation of RAM SEU cros -section as f un tion of neutron/proton energ 4

Fig re 9 – Neutron an proton SEU bit cros -section data 4

Fig re 10 – SEU cros -section in SRAMs as f un tion of the man facture date 51

Fig re 1 – SEU cros -section in DRAMs as fu ction of man f acture date 5

Fig re E.1 – Integral l ne r energ tran f er sp ctra in si con at 10 0 0 ft (3 4 0 m) f or c t-of f rigidities (R) f rom 0 GV to 17 GV 7

Fig re E.2 – Integral l ne r energ tran fer sp ctra in si con at 7 0 0 f t (2 8 0 m) f or c t-of rigidities (R) f om 0 to 17 GV 7

Fig re E.3 – Integral l ne r energ tran fer sp ctra in si con at 5 0 0 f t (16 7 0 m) f or c t-of rigidities (R) f om 0 GV to 17 GV 7

Fig re E.4 – In uen e of solar mod lation on integral l ne r energy tran f er sp ctra in si con at 15 0 0 f t (4 7 0 m) f or c t-of rigidities (R) of 0 GV an 8 GV 7

Fig re E.5 – In uen e of solar mod lation on integral l ne r energy tran f er sp ctra in si con at 5 0 0 ft (16 7 0 m) for c t-of f rigidities (R) of 0 GV an 8 GV 7

Fig re E.6 – Calc lated contribution fom neutron , proton an he v ion to the

SEU rates of the Hitac i-A 4 Mbit SRAM as a fu ction of altitu e at a c t-of rigidity (R)

of 0 GV 7

Fig re E.7 – Calc lated contribution f rom neutron , proton an he v ion to the

SEU rates of the Hitac i-A 4 Mbit SRAM as a fu ction of altitu e at a c t-of f rigidity

(R) of 8 GV 7

Fig re F.1 – Example diff erential LET sp ctrum 81

Fig re F.2 – Example integral c ord len th distribution for isotro ic p rticle

en ironment 81

Fig re G.1 – Variation of the hig energ neutron SEU cros -section p r bit as a

f un tion of electronic device fe ture size for SRAMs an SRAM ar ay in

micro roces ors an FPGAs 8

Fig re G.2 – Variation of the hig energ neutron SEU cros -section p r bit as a

f un tion of electronic device fe ture size for DRAMs 8

Fig re G.3 – Variation of the hig energ neutron SEU cros -section p r electronic

device as a fu ction of electronic device fe ture size f or NOR an NAND type flas

memories 8

Fig re G.4 – Variation of the MCU/SBU p rcentage as a f un tion of f eature size b sed

on data f rom man rese rc ers in SRAMs [4 , 4 ] 8

Fig re G.5 – Variation of the hig energ neutron SEFI cros -section in DRAMs as a

f un tion of electronic device fe ture size 8

Fig re G.6 – Variation of the hig energ neutron SEFI cros -section in

micro roces ors an FPGAs as a fu ction of electronic device fe ture size 9

Fig re G.7 – Variation of the hig energ neutron sin le event latc -up (SEL) cros

-section in CMOS devices (SRAMs, proces ors) as a fu ction of electronic device

f eature size 91

Fig re G.8 – Sin le event burnout (SEB) cros -section in p wer electronic devices

(4 0 V to 1 2 0 V) as a fu ction of drain-source voltage (V

DS) 9

Ta le 1 – Nomen lature cros referen e 3

Ta le B.1 – Sources of hig energ proton or neutron SEU cros -section data 6

Ta le B.2 – Some models for the u e of he v ion SEE data to calc late proton SEE

data 61

Ta le D.1 – Variation of 1 MeV to 10 MeV neutron flu in the atmosphere with altitu e 7

Ta le D.2 – Variation of 1 MeV to 10 MeV neutron flu in the atmosphere with latitu e 7

Ta le G.1 – Information relevant to neutron-in u ed SET 9

Ta le H.1 – Ap roximate SEU energ thres old f or SRAM-b sed devices 9

Ta le H.2 – Neutron flu es a ove diff erent energ thres old (4 0 0 ft, latitu e 4 °) 9

INTERNATIONAL ELECTROTECHNICAL COMMISSION

_

PROCESS MANA GEMENT FOR A VIONICS –

Part 1: A ccommodation of atmospheric radiation ef fects via

single event effects within avionics electronic equipment

1 Th Intern tio al Ele trote h ic l Commis io (IEC) is a worldwid org niz tio for sta d rdiz tio c mprisin

al n tio al ele trote h ic l c mmite s (IEC Natio al Commite s) Th o je t of IEC is to promote

intern tio al c -o eratio o al q e tio s c n ernin sta d rdiz tio in th ele tric l a d ele tro ic f i ld To

this e d a d in a ditio to oth r a tivitie , IEC p bls e Intern tio al Sta d rd , Te h ic l Sp cif i atio s,

Te h ic l Re orts, Pu lcly Av ia le Sp cific tio s (P S) a d Guid s (h re f ter refer e to a “IEC

Pu lc tio (s)”) Th ir pre aratio is e tru te to te h ic l c mmite s; a y IEC Natio al Commite intere te

in th s bje t d alt with ma p rticip te in this pre aratory work Intern tio al g v rnme tal a d n n

-g v rnme tal org niz tio s laisin with th IEC als p rticip te in this pre aratio IEC c la orate clo ely

with th Intern tio al Org niz tio f or Sta d rdiz tio (ISO) in a c rd n e with c n itio s d termin d b

a re me t b twe n th two org niz tio s

2) Th f ormal d cisio s or a re me ts of IEC o te h ic l maters e pre s, a n arly a p s ible, a intern tio al

c n e s s of o inio o th rele a t s bje ts sin e e c te h ic l c mmite h s re re e tatio f rom al

intere te IEC Natio al Commite s

3) IEC Pu lc tio s h v th form of re omme d tio s f or intern tio al u e a d are a c pte b IEC Natio al

Commite s in th t s n e Whie al re s n ble ef forts are ma e to e s re th t th te h ic l c nte t of IEC

Pu lc tio s is a c rate, IEC c n ot b h ld re p n ible for th wa in whic th y are u e or f or a y

misinterpretatio b a y e d u er

4) In ord r to promote intern tio al u if ormity, IEC Natio al Commite s u d rta e to a ply IEC Pu lc tio s

tra s are tly to th ma imum e te t p s ible in th ir n tio al a d re io al p blc tio s An div rg n e

b twe n a y IEC Pu lc tio a d th c re p n in n tio al or re io al p blc tio s al b cle rly in ic te in

th later

5) IEC its lf d e n t pro id a y ate tatio of c nf ormity In e e d nt c rtific tio b die pro id c nf ormity

a s s me t s rvic s a d, in s me are s, a c s to IEC mark of c nf ormity IEC is n t re p n ible f or a y

s rvic s c rie o t b in e e d nt c rtif i atio b die

6) Al u ers s o lde s re th t th y h v th late t e itio of this p blc tio

7) No la i ty s al ata h to IEC or its dire tors, emplo e s, s rv nts or a e ts in lu in in ivid al e p rts a d

memb rs of its te h ic l c mmite s a d IEC Natio al Commite s f or a y p rs n l injury, pro erty d ma e or

oth r d ma e of a y n ture wh ts e er, wh th r dire t or in ire t, or for c sts (in lu in le al f ee ) a d

e p n e arisin o t of th p blc tio , u e of, or rela c u o , this IEC Pu lc tio or a y oth r IEC

Pu lc tio s

8) Ate tio is drawn to th Normativ refere c s cite in this p blc tio Us of th refere c d p blc tio s is

in is e s ble for th c r e t a plc tio of this p blc tio

9) Ate tio is drawn to th p s ibi ty th t s me of th eleme ts of this IEC Pu lc tio ma b th s bje t of

p te t rig ts IEC s al n t b h ld re p n ible f or id ntif yin a y or al s c p te t rig ts

International Stan ard IEC 6 3 6-1 has b en pre ared by IEC tec nical commit e 10 :

Proces management f or avionic

This secon edition cancels an re laces the first edition publs ed in 2 12 This edition

con titutes a tec nical revision

This edition in lu es the fol owin sig if i ant tec nical c an es with resp ct to the previou

edition:

a) removed, in Clau e 7 related to s stem desig , referen e to level A Type I an Typ I

(s stem an ref eren es) As Clau e 7 is now for g idan e, ”s al” statements have b en

c an ed to “s ould” an in 9.5.2 the req irement for electronic comp nent management is

clarified;

b) al c r ent definition in lu ed in Clau e 3 are those u ed within the IEC 6 3 6 f ami y of

e) referen e ad ed in 7.1 to a pro osed new Part 7 o in orp ratin atmospheric radiation

ef fects analy is into the s stem desig proces ;

f ) referen e ad ed in 6.2.10 d) to a pro osed future Part 8 on other p rticles in lu in

proton , pion an muon ;

g) clarification on calc latin event rates where cros -section have b en o tained with non

-atmospheric radiation lke neutron sources, ad ition of a new An ex H, an c an es to 5.3

an 8.2

The text of this stan ard is b sed on the fol owin doc ments:

Ful inf ormation on the votin f or the a proval of this stan ard can b foun in the re ort on

votin in icated in the a ove ta le

This publ cation has b en drafted in ac ordan e with the ISO/IEC Directives, Part 2

A l st of al the p rts in the IEC 6 3 6 series, publs ed u der the general title Pro es

ma a eme t for a io ics – Atmosp eric rad iation efe ts, can b f ou d on the IEC we site

The commit e has decided that the contents of this publ cation wi remain u c an ed u ti

the sta i ty date in icated on the IEC we site u der "ht p:/we store.iec.c " in the data

related to the sp cif i publ cation At this date, the publ cation wi b

• with rawn,

• re laced by a revised edition, or

A bi n ual version of this publcation may b is ued at a later date

IMPORTANT – The 'colour inside' logo on the cov r pa e of this publ c tion in ic te

that it contains colours whic are consid re to be us f ul f or the cor e t

understa din of its conte ts Us rs s ould th ref ore print this doc me t using a

colour printer

This in u try-wide International Stan ard informs avionic s stems desig ers, electronic

eq ipment man facturers, comp nent man facturers an their c stomers of the kin of

ionisin radiation en ironment that their devices wi b s bjected to in aircraft, the p tential

ef fects this radiation en ironment can have on those devices, an some general a pro c es

f or de l n with these eff ects

The same atmospheric radiation (neutron an proton ) that is resp n ible f or the radiation

exp s re that crew an p s en ers ac uire whie f l in is also resp n ible for cau in the

sin le event eff ects (SEE) in the avionic electronic eq ipment There has b en mu h work

car ied out over the last few ye rs related to the radiation exp s re of aircraf t p s en ers an

crew A stan ardised in u try a pro c on the ef fect of the atmospheric neutron on

electronic s ould b viewed as con istent with, an an exten ion of, the on-goin activities

related to the radiation exp s re of aircraf t p s en ers an crew

Atmospheric radiation eff ects are one f actor that could contribute to eq ipment hard an sof t

f ault rates From a s stem saf ety p rsp ctive, u in derived fault rate values, the existin

methodology des rib d in ARP4 5 A (ac ommodation of hard an sof t f ault rates in general)

wi also ac ommodate atmospheric radiation ef fect rates

In ad ition, this International Stan ard refers to the JEDEC Stan ard JESD 8 A, whic relates

to soft er ors in electronic by atmospheric radiation at grou d level (at altitu es les than

10 0 0 ft (3 0 0 m)

PROCESS MANA GEMENT FOR A VIONICS –

Part 1: A ccommodation of atmospheric radiation ef fects via

single event effects within avionics electronic equipment

This p rt of IEC 6 3 6 is inten ed to provide g idan e on atmospheric radiation ef fects on

avionic electronic u ed in aircraf t o eratin at altitu es up to 6 00 ft (18,3 km) It defines

the radiation en ironment, the eff ects of that en ironment on electronic an provides desig

con ideration f or the ac ommodation of those eff ects within avionic s stems

This International Stan ard is inten ed to help avionic eq ipment man facturers an

desig ers to stan ardise their a pro c to sin le event eff ects in avionic by providin

g idan e, le din to a stan ard methodolog

Detai s of the radiation en ironment are provided together with identification of p tential

problems cau ed as a res lt of the atmospheric radiation received Ap ro riate method are

given for q antifyin sin le event eff ect (SEE) rates in electronic comp nents The overal

s stem saf ety methodolog s ould b exp n ed to ac ommodate the sin le event ef fects

rates an to demon trate the s ita i ty of the electronic for the a pl cation at the comp nent

an s stem level

The f ol owin doc ments, in whole or in p rt, are normatively ref eren ed in this doc ment an

are in isp n a le f or its a pl cation For dated ref eren es, only the edition cited a ples For

u dated referen es, the latest edition of the referen ed doc ment (in lu in an

amen ments) a pl es

IEC TS 6 2 9-1:2 15, P ro es ma a eme t for avio ics – Man g me t plan – Part 1:

Pre aration a d maint en n e ofa ele tro ic c mp n nts ma a eme t plan

IEC 6 3 6-2:2 12, P ro es ma a eme t for a ionics – At mosp eric rad iation efe ts –

P art 2: Guidelines for sin le event efe ts test in for a io ics systems

IEC 6 3 6-3, P ro es ma a eme t for avio ics – At mosp eric rad iatio efe ts – Part 3:

System d esig o t imization t o a c mmod ate t he sin le event efe ts (SEE) of atmosp eric

rad iat ion

IEC 6 3 6-4:2 13, P ro es ma a eme t for a ionics – Atmosp eric rad iat io efe ts –

P art 4: Desig of high volta e aircraft electro ics ma a ing p t ent ial sin le event efe ts

IEC 6 3 6-5, P ro es ma a eme t for avio ics – Atmosp eric rad iat io efe ts – P art 5:

As es me t of t hermal n utro flux es a d single e e t efe ts in avionics systems

EIA-4 9 , Sta dard for P re aring a Ele tro ic Comp n nts Man g me t P la

3 Terms and def initions

For the purp ses of this doc ment, the f ol owin terms an def i ition a ply

NOT Us rs of this intern tio al sta d rd c n u e altern tiv d f i itio s c n iste t with c n e tio within th ir

c mp nie

3.1

doc ments relatin to avionic whic are publ s ed by the Society of Automotive En ine rs

Note 1 to e try: For e uipme t, a aia i ty is th f ra tio of time th e uipme t is fu ctio al divid d b th total

time th e uipme t is e p cte to b o eratio al ie th timeth e uipme t is f un tio al plu a y re air time

3.4

a ionic e uipme t e vironme t

< eronautical eq ipment> a pl ca le en ironmental con ition (as des rib d p r the

eq ipment sp cif i ation) that the eq ipment is a le to with tan without los or degradation in

eq ipment p rf orman e d rin al of its man f acturin c cle an maintenan e l f e

Note 1 to e try: Th le gth of th mainte a c lf e is d fin d b th e uipme t ma ufa turer in c nju ctio with

proces of testin a sample of comp nents to determine the key electrical p rameter values

that can b exp cted of al prod ced comp nents of the typ tested

comp ne t ma ufa turer

organisation resp n ible for the comp nent sp cification an its prod ction

3.10

could not d pl c te

CND

re orted outcome of diag ostic testin on a piece of eq ipment

Note 1 to e try: Folowin re eipt of a eror or fa lt me s g d rin o eratio , th eror or f ault c n itio c uld

critical c arge

smal est c arge that wi cau e an SEE if injected or de osited in the sen itive volume

Note 1 to e try: For ma y ele tro ic c mp n nts, th u it a ple is th pic c ulomb (pC); h we er, for smal

g ometry c mp n nts, this p rameter is me s re in femto c ulomb (f C)

3.12

cros -s ction

σ

<in proton an neutron interaction > combination of sen itive are an pro a i ty of an

interaction de ositin the critical c arge for a SEE

Note 1 to e try: Th cro s-s ctio ma b c lc late u in th f olowin formula:

s stem or eq ipment methodolog to test a digital word of information to determine if it has

b en cor upted, an if cor upted, to conditional y a ply a cor ection

Note 1 to e try: This meth d lo y c n c r e t two-bit c ru tio s a d c n d te t a d re ort thre -bit c ru tio s

(Us d within IEC 6 3 6-3.)

3.14

digital single e e t tra sie t

DSET

spuriou digital sig al or voltage, in u ed by the de osition of c arge by a sin le p rticle that

can pro agate throu h the circ it p th d rin one cloc c cle

eq ipment man facturer's doc ment that defines the proces es an practices f or a plyin

electronic comp nents to an eq ipment or ran e of eq ipment

Note 1 to e try: Ge eraly, it a dre s s al rele a t a p cts of th c ntrol n c mp n nts d rin s stem d sig ,

d v lo me t, pro u tio , a d p st-pro u tio s p ort

3.17

ele tronic compone t

electrical or electronic device that is not s bject to disas embly without destru tion or

EX MPLE En items, s b-a s mble , ln -e la e ble u its a d s o -e la e ble u its.

3.19

ele tronic f light instrume tation s stem

EFIS

avionic electronic s stem req irin s stem develo ment as uran e level A an f or whic the

pi ot wi b within the lo p (within the control lo p) throu h the piot s stem inf ormation

<semicon u tor commu ity> circ it cel fai ure within an electronic comp nent that can ot b

reset other than by re o tin the s stem or by c cl n the p wer

Note 1 to e try: Su h a faiure c n ma ife t its lf a a s f t f ault in th t it c uld pro id n fa lt fo n d rin

s b e u nt te t a dimp ct th v lu for th MT UR of th LRU

Note 2 to e try: Se als s ft eror

3.2

f irm fa lt

< ircraft fu ction level> faiure that can ot b reset other than by re o tin the s stem or by

c cl n the p wer to the relevant f un tional element

Note 1 to e try: Su h a f ault c n imp ct th v lu f or th MT F of th LRU a d pro id n f ault f ou d d rin th

s b e u nt te t

3.2

f ly-by-wire

FBW

avionic electronic s stem req irin s stem develo ment as uran e level A an f or whic the

pi ot wi not b within the aircraf t sta i ty control lo p

radiation p rticle energ of giga electron volts ( hou an mi ion electron volts)

Note 1 to e try: Th SI e uiv le t e erg is 16 ,2 pic jo le

hard er or

p rmanent or semi-p rmanent damage of a cel by atmospheric radiation that is not

recovera le even by c cln the p wer of f an on

Note 1 to e try: Hard erors c n in lu e S B, S GR a d S L Su h a fa lt wo ld b ma ife t a a h rd f ault a d

c n imp ct th v lu for th MT F of th LRU

3.2

hard f ault

< ircraft f un tion level> p rmanent f ai ure of a comp nent within an LRU

Note 1 to e try: A h rd fa lt re ults in th remo al of th LRU af fe te a d th re la eme t of th p rma e tly

d ma e c mp n nt b fore a s stem/s stem arc ite ture c n b re tore to f ul f un tio alty Su h a fa lt c n

imp ct th v lu for th MT F of th LRU re aire

test methodolog where an LRU is placed within a radiation b am that provides a simulation

of the atmospheric neutron environment an where the inputs to the LRU can b fom an

electronic fixture external to the b am to ena le a closed lo p s stem

Note 1 to e try: Th ele tro ic f i ture c n c ntain a h st c mp ter f or th aircraf t simulatio mo el Th

ele tro ic fixture c n als c ntain a pro riate sig al c n itio in for c mp tibi ty with th LRU In th c s of a

a tomatic c ntrol f un tio , th o tp ts fom th LRU c n b , in turn, s nt to a a tu tio me n or dire tly to th

h st c mp ter Th h st c mp ter wo ld a tomatic ly clo e a sta i ty lo p (a in th c s of a fly-b -wire c ntrol

s stem) In th c s of a n vig tio fu ctio , th o tp ts fom th LRU c uld b s nt to a dis la s stem wh re th

piot c uld th n clo e th n vig tio lo p

3.31

inte rate modular a ionic

IMA

implementation of aircraft f un tion in a multitas computin en ironment where the

computation f or e c sp cific s stem implementin a p rtic lar fu ction are confined to a

p rtition that is exec ted by a common computin resource (a sin le digital electronic circ it

3.3

latc -up

trig erin of a p rasitic p-n-p-n circ it in bulk CMOS, res ltin in a state where the p rasitic

latc ed c r ent ex e d the holdin c r ent

Note 1 to e try: This state is maintain d whie p wer is a ple

Note 2 to e try: L tc -u c n b a p rtic lar c s of a s ft f ault (f irm/s f t eror or in th c s wh re it c u e

ele tro ic c mp n nt d ma e, a h rd fa lt

3.3

l ne r e ergy tra sfer

LET

energy de osited p r u it p th len th in a semicon u tor alon the p th of the radiation

Note 1 to e try: Th u its a plc ble are MeV⋅cm

radiation p rticle energ of mega electron volts (mi ion electron volts)

Note 1 to e try: Th SI e uiv le t e erg is 16 ,2 f emto jo le

Note 1 to e try: MT F is a term fom th world airln s’ te h ic l glo s ry ref erin to th me n time b twe n

f aiure of e uipme t or a s stem in s rvic s c th t it g n raly re uire th re la eme t of a d ma e

c mp n nt b fore a s stem/s stem arc ite ture c n b re tore to ful fu ctio alty a d th s it is a me s re of

rela i ty re uireme ts f or e uipme t or s stems

Note 1 to e try: MT UR is a term f rom th world airln s’ te h ic l glo s ry referin to th me n time b twe n

u s h d le remo al of e uipme t or a s stem in s rvic th t c n b th re ult of s ft f aults a d th s is a me s re

of rela i ty for e uipme t or s stems MT UR v lu s c n h v a major imp ct o airln o eratio al c sts

3.3

multiple bit ups t

MBU

energ de osited in the si con of an electronic comp nent by a sin le ionisin p rticle an

whic cau es upset to more than one bit in the same word

Note 1 to e try: Th d f i itio of MBU h s b e u d te d e to th intro u tio of th d f i itio of MC , multiple

c l u s t

3.4

multiple c l ups t

MCU

energ de osited in the si con of an electronic comp nent by a sin le ionisin p rticle an

whic in u es several bits in an integrated circ it (IC) to upset at one time

3.41

ne tron

elementary p rticle with atomic mas n mb r of one an whic car ies no c arge

Note 1 to e try: It is a c n titu nt of e ery atomic n cle s e c pt h dro e

3.4

no fa lt f ound

NFF

re orted outcome of diag ostic testin on a piece of eq ipment

Note 1 to e try: Folowin re eipt of a eror or fa lt me s g d rin o eratio , th e uipme t is f ou d to b f uly

f un tio al a d within s e if i atio d rin s b e u nt e uipme t te tin Se IEC 6 3 6-3

particle f lue c

<u idirectional b am of p rticles> n mb r of p rticles cros ing the u it s rf ace are at rig t

an les to the b am

Note 1 to e try: For is tro ic f l x, this is th n mb r e terin a s h re of u it cro s-s ctio al are

Note 2 to e try: Th u its a plc ble are p rticle⋅cm

3.4

pion

s b-atomic p rticle

Note 1 to e try: Th c arg p s ibi tie are (+1, –1, 0) a d th y are pro u e b e erg tic n cle r intera tio s

Note 2 to e try: Th term “pi-me o ” c n b u e in le of pio ” in s me d c me ts or sta d rd

3.4

prel minary s stem s fety a s s me t

PSSA

s stematic evaluation of a pro osed s stem arc itecture an implementation b sed on the

f un tional hazard as es ment an fai ure con ition clas ification to determine safety

f or a s stem with con tant fai ure rate, the con itional pro a i ty that a s stem wi remain

o erational over the time interval 0 to t given by:

me s re of the p tential ina i ty to ac ieve overal program o jectives within defined cost,

s hed le, an tec nical con traints

3.5

single bit ups t

SBU

<semicon u tor device radiation a sorb d by the electronic comp nent whic is s f ficient to

c an e a sin le cel s logic state

Note 1 to e try: After a n w write c cle, th origin l state c n b re o ere

_ _ _ _ _ _

1

Numb rs ins u re bra k ts ref er to th Biblo ra h

single e e t burnout

SEB

burnout of a p wered electronic comp nent or p rt there f as a res lt of the energ

a sorption trig ered by an in ivid al radiation event

3.5

sin le er or cor e tion, double er or dete tion

SECDED

s stem or eq ipment methodolog to test a digital word of information to determine if it has

b en cor upted, an if cor upted, to con itional y a ply a cor ection

Note 1 to e try: This meth d lo y c n c r e t o e-bit c ru tio a d c n d te t a d re ort two-bit c ru tio s

3.5

single e e t ef fe t

SEE

resp n e of a comp nent cau ed by the imp ct of a sin le p rticle (f or example galactic

cosmic ray , solar energetic p rticles, energetic neutron an proton )

Note 1 to e try: Th ra g of re p n e c n in lu e b th n n-d stru tiv (f or e ample u s t) a d d stru tiv (or

e ample latc -u or g te ru ture) p e ome a

3.5

single e e t functional inter upt

SEFI

oc ur en e of an upset, u ual y in a complex electronic comp nent (e.g a micro roces or),

s c that a control p th is cor upted, le din the electronic comp nent to ce se to f un tion

<gate of a p wered in ulated gate comp nent> radiation c arge a sorb d by the electronic

comp nent, whic is s ff i ient to cau e gate rupture an is destru tive

3.5

single e e t latc -up

SEL

in an electronic comp nent containin a minimum of 4 semicon u tor layers (p-n-p-n), fixed

state of a comp nent that oc urs when the radiation a sorb d by the comp nent is s ff i ient

to cau e a node within the p wered semicon u tor comp nent to b held whatever input is

a pl ed u ti the comp nent is de-p wered

Note 1 to e try: Sin le e e t latc -u c n b d stru tiv or n n-d stru tiv

Note 2 to e try: Th io iz tio d p site b th intera tio of a sin le p rticle of ra iatio in a ele tro ic

c mp n nt c u e trig erin of a p ra itic p-n-p-n circ it in s mic n u tor materials (in lu in b lk CMOS) to

o c r, re ultin in a state wh re th p ra itic latc e c re t e c e s th h ldin c re t; this state is maintain d

whie p wer is a ple Sin le e e t latc -u c n b a p rtic lar c s of a s f t f ault (irm/s ft eror or in th c s

wh re it c u e ele tro ic c mp n nt d ma e, a h rd fa lt

3.5

single e e t tra sie t

SET

momentary voltage ex ursion (voltage spike) at a node in an integrated circ it cau ed by a

sin le energetic p rticle strike

Note 1 to e try: Th s e if i terms AS T (a alo u sin le e e t tra sie t) a d DS T (digital sin le e e t

<semicon u tor comp nent> radiation a sorb d by the electronic comp nent whic is

s f ficient to c an e a cel s logic state

Note 1 to e try: After a n w write c cle, th origin l state c n b re o ere

Note 2 to e try: A lo ic c l ma b a memory bit c l re ister bit c l latc c l etc

3.5

single hard er or

SHE

single e e t induc d hard er or

radiation (in a sin le event a sorb d by the electronic comp nent, whic is s f ficient to

cau e a p rmanent stu k-bit in the comp nent, an a hard er or within the eq ipment

3.6

sof t er or

er one u output sig al fom a latc or memory cel that can b cor ected by p rormin one

or more normal f un tion of the electronic comp nent containin the latc or memory cel

Note 1 to e try: As c mmo ly u e , th term ref ers to a eror c u e b ra iatio or ele troma n tic p ls s a d

n t to a eror a s ciate with a p y ic l d fe t intro u e d rin th ma uf acturin pro e s

Note 2 to e try: Sof t erors c n b g n rate f rom S U, S FI MBU, MC , a d or S T Th term S R h s b e

a o te b th c mmercial in u try whie th more s e ific terms S U, S FI etc ar e ty ic ly u e b th

a io ic , s a e a d mi tary ele tro ic c mmu itie

Note 3 to e try: Th term “s f t eror” wa f irst intro u e (or DRAMs a d ICs) b Ma a d Wo d of Intel in th ir

Apri 19 8 p p r at th IE E Intern tio al Rela i ty Ph sic Symp sium (IRPS) [13 ] a d th term “sin le e e t

u s t wa intro u e b Gu n er, Wolc i a d Ala of Na al Re e rc L b ratory, Wa hin to D , in th ir 19 9

IE E Nu le r & Sp c Ra iatio Ef fe ts Co f ere c (NSREC) p p r [13 ]

3.61

sof t fa lt

< ircraft fu ction level> c aracteristic of in al d digital logic cel (s) state c an es within digital

hardware electronic circ itry

Note 1 to e try: It is a f ault th t d e n t in olv re la eme t of a p rma e tly d ma e c mp n nt within a

LRU b t it d e in olv re torin th lo ic c ls to v ld state b f ore a s stem/s stem arc ite ture c n b re tore

to ful fu ctio alty Su h a fa lt c n itio h s b e s s e te in th "n f ault fo n " s n rome f or f un tio s

impleme te with digital te h olo y a d it c n pro a ly imp ct th v lu for th MT UR of th in olv d LRU If a

s ft f ault re ults in th mista e re la eme t of a c mp n nt within th LRU, th re la eme t c n imp ct th v lu

en an ement of solar p rticles (proton , ion an some neutron ) cau ed by solar flare

activity or coronal mas ejection

Note 1 to e try: Th e h n eme t c n la t f rom a few h urs to s v ral d y A smal f ra tio h s s ff i ie tly

e erg tic s e tra to pro u e sig ific ntly e h n e s c n ary n utro flu e in th atmo p ere

3.6

s bstitute compone t

comp nent u ed as a re lacement in eq ipment after the eq ipment desig has b en

a proved

Note 1 to e try: In s me c nte ts, th term “altern te c mp n nt is u e to d s rib a s b titute c mp n nt th t

is “e u l to or b ter th n” th origin l c mp n nt

mitigation ac ieved f or certain typ s of SEE by control of certain stres ors within defined

p rameters in the a plcation

Note 1 to e try: For e ample S L a d S B c n b 10 % mitig te b lmitin s p ly v lta e b low th thre h ld

wh re S L a d S B o c r

3.6

v l dation

method of confirmation of comp nent radiation toleran e by the eq ipment man facturer,

when there is no in-service data fom prior u e or radiation data f rom a test la oratory

3.6

white ne tron sourc

source providin energetic neutron with a wide ran e of energies, the sp ctrum of whic is

simi ar to that of the natural atmospheric or ter estrial radiation up to the maximum energ of

the source

BL1A, BL1B, BL C b am l ne desig ation at the TRIUMF f aci ty (Canada) [se

IEC 6 3 6-2]

DOE De artment of Energ (USA)

IEC 6 3 6-2]

IEEE Tran Nu l Sci IEEE Tran action on Nu le r Scien e

LRU lne re lace ble u it

MOSFET metal oxide semicon u tor field ef fect tran istor

radiation a sorb d dose

IEC 6 3 6-2]

SECDED sin le event cor ection double event detection

SW software

5 Radiation e vironme t of the atmosphere

5.1 Ra iation ge eration

The atmosphere is p netrated by a flu of variou c arged an neutral p rticles that in

combination cre te a complex ionisin radiation en ironment These p rticles are cre ted by

the interaction of the contin ou stre m of primary cosmic ray p rticles with the atoms in the

atmosphere (mainly nitrogen an ox gen), an so are caled secon ary cosmic ray The

primary cosmic ray are u ual y refer ed to as galactic cosmic ray (GCR), in icatin that

their origin are b yon that of the solar s stem

The galactic cosmic radiation is comp sed of atomic n clei that have b en completely ionised

(ful y strip ed of their electron ) an s bseq ently ac elerated to very hig energies GCR

con ist of a out 8 % proton , 16 % alpha p rticles an < 2 % he v ion (p rticles with

atomic n mb r Z > 2) As the primary cosmic ray , mainly very hig -energ proton , b mb rd

the atmosphere, they cre te a cas ade of secon ary, tertiary, etc p rticles f om their

interaction with the atoms of the atmosphere Th s, f or e c primary cosmic ray enterin ,

man more secon ary p rticles are cre ted At a very a proximate level, the flu of in omin

primary cosmic ray at the to of the atmosphere is 3 p rticle⋅cm

-2

⋅s-

, an at aircraf t

altitudes, the f l x of al secon ary p rticles is a out 10 p rticle⋅cm

-2

⋅s-

The den ity of the

lowest p rtion of atmosphere is so hig , that most of the flu of p rticles is a sorb d, so that

at se level the nominal flu of secon ary p rticles is les than 0,1 p rticle⋅cm

-2

⋅s-

The f l x of secon ary p rticles is not u iform arou d the e rth d e to the ef fect of the e rth’s

mag etic f ield that is at rig t an les to the p rticle direction at the eq ator Particles cros

field l nes at rig t an les at the eq ator an are b nt away, whi e at the p les they travel

p ral el to the f ield an are not deflected As a res lt the primary cosmic ray are a le to

p netrate into the atmosphere more re di y ne r the mag etic p les an they interact with the

atoms in the atmosphere cre tin larger n mb rs of cas ade p rticles

5.2 Ef fe t of s con ary particle on a ionic

Some of the secon ary p rticles can interact with electronic devices within aircraft avionic

s stems an cau e single event eff ects (SEEs) in the devices These secon ary p rticles

de osit enou h c arge throu h the recoi s they cre te within a sen itive p rtion of a device to

res lt in a malfu ction of the device It has b en f ou d that neutron , proton an pion are

the main p rticles that can cau e these ef fects

5.3 Atmospheric ne trons

Neutron are the secon ary cosmic ray p rticles that have b en s own to b mainly

resp n ible for cau in sin le event upsets (SEUs) in memories an other electronic devices

on aircraft sin e the e rly 19 0s This identification of the neutron as the main cau e of the

SEUs was b sed on several dif ferent kin s of cor elation :

a) the variation of the upset rates again t altitu e an ge gra hic latitu e fol owed the

variation of the neutron f l x with altitu e an latitu e;

b) neutron-in u ed SEU rates calc lated u in SEU cros -section me s red in a lab ratory

an integrated with the neutron flu in the atmosphere agre d with me s red in-l g t SEU

rates; an

c) upset rates at grou d level d e to secon ary neutron are pro ortional to rates at aircraf t

altitu es F r the neutron , as wel as al for the secon ary p rticles within the

atmosphere, the variation of the p rticle flu with thre p rameters (energ , altitu e an

latitu e) is most imp rtant f or u derstan in the variation of the SEU rate

5.3.2 Atmospheric ne trons e ergy spe trum a d SEE cros -s ctions

5.3.2.1 Natural e ergy spe trum of atmospheric n utrons

The energ variation of the atmospheric neutron is u ual y presented by plotin the

dif ferential flu (f l x p r u it energ interval) as a f un tion of energy, whic is of ten caled the

sp ctrum (se Fig re 1) Monte Carlo generated sp ctra have prod ced the fol owin

f raction < 1 MeV 0,5 ; 1 MeV to 10 MeV 0,2; > 10 MeV 0,2 The f its q oted b low may give

sl g tly dif ferent values Me s rements of the energ sp ctrum of the cosmic ray neutron

have b en made sin e the 19 0s u in a variety of tec niq es In Fig re 1 f our neutron

sp ctra at an altitu e of a proximately 40 0 0 f t (12,2 km) are plot ed These in lu e the

original me s rements made by Hes in 19 9 [1] a calc lation by Armstron in 19 3 [2] a fit

to me s rements by Hewit et al at NASA in 19 7 [3] an the recent DOE me s rements by a

f it to me s rement by Gold agen in an ER-2 aircraf t d rin 19 7 [4]

Fig re 1 – Energy spe trum of atmospheric ne trons

at 4 0 0 f t (12 16 m), latitude 4 °

A fit to the NASA Ames Rese rc Center’s 19 4 f lig t data (energ (E) up to 3 0 MeV) that

had b en u ed in the p st has b en modif ied for energ > 3 0 MeV u in the more recent

me s rement data It s ould b noted that when this diff erential flu is integrated for energ

10 MeV, the integrated neutron flu is ~ 6 0 neutron⋅cm

-2

⋅h-

whic can b rou ded up to

6 0 0 neutron⋅cm

-2

⋅h-

This nominal hig energ neutron flu of 6 0 0 neutron⋅cm

-2

⋅h-

at

4 0 0 f t (12,2 km) an ge gra hic latitu e 4 ° may be tre ted as a typical or nominal in

-fl g t en elo e an s aled for dif ferent avionic a plcation (for example, for altitu e

variation p r me s rements) The modified sp ctrum is given, with energ in MeV, as

1×100

1×10–1

1×10–2

1×10–3

1×10–4

1×10–5

1×10–3

1×10–2

1×10–1

1×100

1×101

1×102

1×103

1×104

It s ould b noted that when this dif ferential flu is integrated for energ > 10 MeV, the

integrated neutron f l x is ~ 6 0 neutron⋅cm

-2

⋅h-

6 0 0 neutron⋅cm

-2

⋅h-

This nominal hig energ neutron flu of 6 0 0 neutron⋅cm

-2

⋅h-

at

4 0 0 ft (12,2 km) an ge gra hic latitu e 4 ° may b tre ted as a typical or nominal in

-fl g t en elo e an s aled for diff erent avionic a plcation (f or example, for altitu e

variation as in 5.3.3 an for latitu e variation as in 5.3.4) For lower energies, the model gives

a f l x of 3 2 0 neutron⋅cm

-2

⋅h-

for 1 MeV < E < 10 MeV, with 1 6 0 neutron⋅cm

-2

⋅h-

in the

ran e of 1 MeV< E < 3 MeV an 1 6 0 neutron⋅cm

-2

⋅h-

in the ran e of 3 MeV < E < 10 MeV

This flu of 6 0 0 neutron⋅cm

-2

⋅h-

f or E > 10 MeV is con ervative by a factor of a proximately

2 comp red to the ER-2 aircraf t me s rement res lts At grou d level the f l x is

a proximately a f actor of 3 0 lower than at 4 0 0 f t (12,2 km), th s on the grou d, the f l x

f or energ > 10 MeV is 2 neutron⋅cm

-2

⋅h-

, [5] an this agre s with an in e en ently derived

calc lation f or New York City [6]

The gre ter than 10 MeV neutron wi b the dominant cau e of SEE on sen itive electronic

devices with ge metric f eature size a ove 15 nm, however for devices with f eature size at

an b low 15 nm the contribution of neutron with energ b twe n 1 MeV an 10 MeV may

b sig if i ant Theref ore for electronic device f eature sizes 15 nm an b low the ef fects d e

to neutron with energ in the ran e 1 MeV < E < 10 MeV s al b in lu ed when calc latin

SEE rates

In order to make relevant SEE calc lation for electronic devices with fe ture sizes b low

15 nm, it can b valua le to u derstan how the avai a le SEE cros -section(s) was/were

determined

5.3.2.2 White ne tron spe trum cros -s ctions

If the avai a le cros -section(s) was/were determined f rom neutron exp riments where a

white neutron energ sp ctrum re resentative of the atmospheric sp ctrum was u ed ( he test

b am in lu es neutron with energ in the ran e 1 MeV < E < 10 MeV an a ove 10 MeV,

re resentative of the atmospheric sp ctrum), the exp rimental res lts in lu e SEE cau ed by

neutron with energ in the ran e 1 MeV < E < 10 MeV Theref ore, the calc lated cros

-section in lu es those SEE contribution fom neutron with energ in the ran e

1 MeV < E < 10 MeV (if an ) For those cros -section , the neutron f l en e ref eren e energ

original y u ed to calc late the cros -section (if JESD 8 A is u ed, the neutron fluen e at

10 MeV is sp cified) provides the key for the a plca le energ ran e for the u e of neutron

f l x that wi yield a pro riate u e con ition SEE rates Faci ties whic provide hig energy

white neutron radiation sources in lu e WNR, TRIUMF (TNF), ISIS (RAL), ANITA (TSL) an

ter estrial faci ties

Becau e a cros -section me s red with a white sp ctrum atmospheric neutron b am contain

SEE contribution at lower energies, the white neutron sp ctrum cros -section can b u ed

without modification f or al energ ran es covered by the cros -section tests For example,

for cros -section me s red in a white neutron sp ctrum b am an f ol owin JESD 8 A

(JESD 8 A sp cifies the cros -section b calc lated u in the 10 MeV fluen e), the nominal

neutron flu at 10 MeV of 6 0 0 neutron⋅cm

-2

⋅h-

, may b u ed to determine the a pro riate

SEE rate Th s the nominal event rate f or s c cros -section (E > 10 MeV) is given by:

Nominal event rate = cros -section (E > 10 MeV) × 6 0 0 events p r hour

Sometimes the white neutron cros -section are q oted for neutron with energ a ove

1 MeV, an the nominal event rate for s c cros -section (E >1 MeV) is then given by:

Nominal event rate = cros -section (E > 1 MeV) × 9 2 0 events p r hour

Usin cros -section an flu es b sed on a > 1 MeV thres old introd ces ad itional

u certainty Therefore, this s ould only b done if, for some re son, the > 10 MeV cros

-section is u avai a le

5.3.2.3 Non-white ne tron spe trum cros -s ctions or unk own cros -s ctions

For cases where the SEE cros -section were me s red by method where the SEE

contribution f rom neutron with energ in the ran e 1 MeV < E < 10 MeV p tential y have not

b en in lu ed, the contribution f om these lower energy ran es can b estimated for some

electronic devices by u in an en an ed fig re for neutron flu in the er or rate calc lation

Non-atmospheric sp ctrum b am typ s in lu e mono-energetic proton b ams an q asi

-mono-energetic neutron b ams Becau e b am sp ctra are not re resentative of the natural

atmospheric radiation sp ctra the toleran e on the er or rate is larger than in 5.3.2.2

• F r electronic devices with fe ture size a ove 16 nm the nominal SEE rate is calc lated

u in the E > 10 MeV cros -section an nominal neutron flu of 6 0 0 neutron⋅cm

-2

⋅h-

For f eature sizes a ove 16 nm this f l x is con idered to b s f ficiently con ervative to

ac ommodate the ef fects f rom lower energ neutron

• For electronic devices with ge metric f eature size 16 nm an b low the ef fects d e to

lower energ neutron s al b in lu ed, an con ideration of the low energ thres old

f or smal er ge metry devices is provided in An ex H Ta le H.1 provides the a proximate

neutron energ thres old vers s electronic device tec nolog fe ture size Ta le H.2

provides the recommen ed nominal neutron f l xes for diff erent electronic device

tec nolog f eature sizes when u in non-white neutron (non-atmospheric l ke) radiation

sources The method to calc late nominal event rates for the smal er ge metry electronic

devices is given in Clau e H.3

NOT 1 Th origin l g id n e b s d o refere c [7] th t th c ntrib tio fom th 1 MeV < E <10 MeV n utro s

to th o eral S E rate is 10 % is n lo g r re omme d d for th smaler g ometry ele tro ic d vic s

NOT 2 Th v lu s of n utro flu giv n in Ta le H.2 c n b s ale to oth r altitu e a d latitu e , u in th

Ta le D.1 a d D.2

5.3.3 Altitude v riation of atmospheric ne trons

The altitu e variation of the atmospheric neutron derives fom the comp tition b twe n the

variou prod ction an removal proces es that af fect how the neutron an the initiatin

cosmic ray interact with the atmosphere The res lt is a maximum in the flu at a out

6 0 0 f t (18,3 km), cal ed the Pf otzer maximum that can b se n in Fig re 2 The f i ure

comp res the altitu e variation of the 1 MeV to 10 MeV neutron flu A mu h more rigorou

a pro c was taken by NASA-L n ley in develo in a model that is c r ently cal ed AIR [10]

It uti sed me s rements made on aircraf t d rin the 19 0s an 19 0s, an develo ed a

model that gives the 1 MeV to 10 MeV neutron f l x as a f un tion of thre p rameters, the

atmospheric de th (g⋅cm

-2

), vertical rigidity c t-of (GV) an solar we ther con ition

A sti more rigorou model has b en develo ed b sed on exten ive calc lation in orp ratin

thre key ste s, the calc lation of the initial cosmic ray sp ctrum, the rigidity c t-of f

calc lation an a Monte Carlo code to generate an tran p rt the secon ary p rticle radiation

throu h the atmosphere This code p c age is cal ed the Quotid Atmospheric Radiation Model

(QARM) [12] an it can b ac es ed an uti sed via the Internet l n [1 ] It can provide

estimates of the secon ary cosmic ray p rticle flu es an sp ctra at al location f or al

p rticles in lu in neutron an proton A simi ar code p c age that is also avai a le via the

Internet is cal ed EXPACS (Ex el-b sed programme f or calc latin atmospheric cosmic- ay

sp ctrum [13]), an is b sed on analytical f un tional f its to Monte Carlo-generated sp ctra

[14] QARM an EXPACS yield simi ar res lts for the atmospheric neutron sp ctrum [15]

Predicted SEU rates in the atmosphere b sed on u in QARM for six diff erent SRAMs are

a out a factor of 2 lower than rates calc lated u in the neutron sp ctrum (se 5.3.2) in this

stan ard [15]

Fig re 2 – Mod l of th atmospheric n utron f lux

v riation with altitude (s e Anne D)

A ta ular des ription of the variation of atmospheric neutron f l x with altitu e an also with

latitu e as given by the Bo in model is provided in An ex D to ena le calc lation of neutron

f l x at variou f lig t location

5.3.4 Latitu e v riation of atmosph ric ne trons

The latitu e variation is expres ed in terms of the vertical rigidity c t-of f (R), in u its of GV

The rigidity c t-of fs in icate the req ired rigidity (es ential y the p rticle momentum divided

by its c arge) of primary cosmic ray p rticles ne ded to p netrate to a given location a ove

the atmosphere At the eq ator, where the mag etic field is at rig t an les to p rticle

direction, it req ires p rticles with the hig est rigidity (R ~ 15 GV) to p netrate to this region,

an where it is p ralel to the p rticle direction, ne r the p les, p rticles with R < 1 GV can

re c The ge gra hical distribution of the vertical rigidity c t-of fs arou d the world at an

altitu e of 2 km [16] is s own in Fig re 3

Fig re 3 s ows the distribution of vertical rigidity c t-of c rves acros the glo e b sed on the

19 0 e oc that was develo ed in [16] combinin me s rements an calc lation , with the

rigidity c t-off s b in averaged over ge gra hical lon itu e for e c 5° in ge gra hical

latitu e The referen e [16] authors updated their rigidity c t-of model with a new set of data

f rom the ye r 19 5 an it is ta ulated in JESD 8 A This newer set of calc lation an

me s rements prod ced a model with rigidity values within 1° × 1° ac urac These rigidity

values were averaged over bro der an ular bin (5° in latitu e × 15° in lon itu e) an these

averaged values are ta ulated in An ex A of JESD 8 A:2 0 Based on a comp rison of the

updated rigidity values f rom JESD 8 A (19 5 e oc ) with the older values in Fig re 3 (19 0

e oc ), the rigidity c t-of values have decre sed sl g tly A comp rison was car ied out at a

lon itu e of 0° an f or latitu es ran in b twe n 3 ° an 6 ° In most cases the c an e was

a decre se of ~ ,15 to 0,2 in the overal vertical rigidity acros al latitu e levels Sin e the

c an e in rigidity was a proximately con tant, the p rcentage c an e was mu h hig er at

hig er latitu es where the a solute value of the rigidity is smal er Th s, for latitu es < 5 °,

the p rcentage decre se was < 5 %, f or 5 ° to 5 ° it was b twe n 5 % an 7 %, an f or 6 ° it

was ~15 % These variation in the vertical rigidity c t-off s d e to c an es in the ge mag etic

f ield over a 15-ye r p riod a p ar to b smal enou h to in icate that the cor esp n in

c an e in the atmospheric neutron flu wi b relatively smal , an Fig re 3 is sti u eful

Ful y up to date c t-of rigidities are avai a le throu h the QARM model [12] u in trajectory

integration in the latest IGRF magnetic field plu external source terms de en ent on the

ge mag etic disturb n e in ex (Kp) u in the Ts ganen o 2 01 model The QARM model

can b ac es ed an uti sed via the internet l n [1 ] These rigidities can b computed on

-l ne f or an selected location For fl g t p th calc lation a set of 4 pre-calc lated ma s is

u ed Ge mag etic disturb n es can sig if i antly lower the c t-of rigidity (by a out a f actor 2

IE C

0

0,2

0,50,7

f or Kp = 6 for a 1 GV c t-of at zero disturb n e) The in uen e on p rticle f l xes can b

a out 10 % for galactic cosmic ray but by factors of 5 or more d rin solar p rticle events

Figure 3 – Distribution of v rtic l rigidity c t of f s aroun the world

Two models are also avaia le f or the variation of the 1 MeV to 10 MeV neutron flu as a

f un tion of latitu e, a simplf ied Bo in model an the NASA-L n ley AIR model The

simpl fied Bo in model is b sed on me s rements made in aircraf t d rin the 19 0s, in

p rtic lar p le-p le latitu e s rvey a o rd a Bo in 7 7 aircraf t [17] The initial data was

given as the neutron f l x as a f un tion of the vertical rigidity c t-off Based on the o servation

in Fig re 3 that the rigidity c t-off s ex ibit their main variation with latitu e, the vertical c

t-of fs were averaged over ge gra hical lon itu e for e c 5° in ge gra hical latitu e These

contours are evolvin with time d e to the Earth's c an in ge mag etic field This al owed

the me s red 1 MeV to 10 MeV neutron flu , original y given as a f un tion of igidity c t-off , to

b con erted to a c rve of the 1 MeV to 10 MeV neutron flu as a f un tion of latitu e an this

The variation of the neutron flu with altitu e s own in Fig re 2 for energies 1 MeV to 10 MeV

has also b en s own to a ply for neutron with hig er energies [9] Theref ore Fig re 2 an

Fig re 4 can b u ed to s ale the gre ter than 10 MeV neutron flu of 6 0 0 neutron⋅cm

-2

⋅h-

whic a ples at 4 0 0 f t (12,2 km) an 4 ° latitu e to other altitu es and latitu es It s ould

b noted that there is a stron de en en e of c t-of rigidity an hen e p rticle flu es on

lon itu e an this is s own in the QARM model F r example, at 4 ° latitu e there is a f actor

5 variation in c t-of f rigidity with lon itu e an this tran lates into a f actor 3 variation in

neutron flu es f om galactic cosmic ray

The 1 MeV to 10 MeV neutron have a sig ificant SEE contribution for electronic devices with

ge metries 15 nm an b low (se 5.3.2)

5.3.5 Thermal ne tron within aircraf t

Thermal neutron are low energ neutron that have s at ered s f ficiently to b in thermal

eq i brium with their s r ou din s At ro m temp ratures this le d to an average energ of

0,0 5 eV The majority of the thermal neutron in ide the aircraf t are cre ted by the

interaction of the aircraft stru ture an al of its contents with the hig er energ neutron

within the atmosphere Thermal neutron can b sig if i ant b cau e they have a very hig

pro a i ty of interactin with certain isoto es, s c as b ron 10 (B10), an b ron is present

in micro lectronic in two main are s, as a p do ant, an in some f orms of the glas ivation

layer, for example b ro hosphosi cate glas Th s, a 0,0 5 eV neutron interactin with a B10

atom le d to two c arged p rticles in an electronic device with a combined 2,3 MeV of

energ ; if this energy is de osited within the sen itive volume of an electronic device, it can

le d to SEU

To date, only one stu y has at empted to calc late the thermal neutron flu within an

a ro lane [18] The h drogenou materials within an a ro lane, the fuel, the p s en ers, the

crew an the b g age, al serve to thermal se the hig er energy neutron An entire large

commercial airl ner was model ed in terms of 2 s b-volumes, some extremely large Even

with this cru e model the calc lation were very u eful, s owin that at the several location

within the a ro lane that were re orted up n, the thermal neutron f l x was a out a factor of

10 hig er than it is ju t outside the a ro lane The n mb r of me s rements of SEU cros

-section in electronic devices in u ed by thermal neutron is very l mited (se 8.3.3), but

more recent referen es sig ificantly exp n on this data [19, 2 , 21, 2 ]

The s bject of thermal neutron ef fects is covered in more detai in IEC 6 3 6-5

5.4 Se ondary protons

Charged p rticles have also b en me s red in the atmosphere, most of whic are, l ke the

neutron , cosmic ray secon aries, fom the interaction of the primary cosmic ray with the

ox gen (O) an nitrogen (N) n clei in the air The secon ary proton can cau e sin le event

ef fects in electronic in a man er very simiar to that of the neutron The distribution of

secon ary proton is simi ar to that of neutron , esp cial y with resp ct to energ an altitu e

The energ sp ctrum of the atmospheric proton is simi ar to that of the neutron , as se n in

Fig re 5, whic contain proton me s rements at two mou tain to s (US an Ru sia, [2 ,

2 ]) an fom one b lo n exp riment [2 ] The mou tain-to data in icates a p akin in the

dif ferential proton flu at a out 2 0 MeV to 3 0 MeV Fig re 5 s ows that for energies up to

a out 5 0 MeV, the secon ary proton in the atmosphere are a out 2 % to 3 % of the flu

of the neutron , but at hig er energies the proton an neutron f l xes are comp ra le

10 MeV < E < 7 0 MeV, the variation with altitu e is very simi ar to that of the neutron [2 ]

i.e there is a maximum at ~ 0 g⋅cm

-2

(5 0 0 f t (16,8 km) , the Pfotzer maximum With

resp ct to the latitu e variation there is a sl g t decre se in the total atmospheric proton flu

of a out a factor of 2 in traversin f om the p lar to eq atorial region , whic is les

pronou ced than the latitu e variation with neutron Therefore, for purp ses of calc latin

SEE rates in the atmosphere, sin e the neutron flu dominates an the s g ested flu of

6 0 0 neutron⋅cm

-2

⋅h-

(E > 10 MeV) is con ervative, the contribution of the proton to the

SEE rate can b con idered as b in in lu ed within the neutron-in u ed SEE rate

Nevertheles as dis u sed in 6.2.10, item c), in the low energ domain, proton may interact

throu h ionization an contribute to the er or rate of tec nologies b low 9 nm

Figure 5 – Energy spe trum of protons within the atmosphere

5.5 Oth r particle

The other c arged p rticle secon ary cosmic ray within the atmosphere that can in u e sin le

event eff ects in electronic is the pion ( here are b th p sitively an negatively c arged

pion ) However, in the atmosphere at aircraft altitu es, the pion f l x is only a smal f raction

of the neutron an proton f l x F r energies ≤ 1 GeV, the pion/proton (π/p) ratio is estimated

to b ~ ,1, an it a pl es at b th aircraft altitu es, 5 0 g⋅cm

-2

(2 0 0 f t (6,1 km) , as wel as

at grou d level [2 ] At 4 0 0 f t (12,2 km) an at an energ of 1 GeV, the dif ferential pion

f l x has b en calc lated to b ~1/3 that of the neutron an proton ( he diff erential neutron

an proton flu es are a out eq al), an at 10 MeV, the dif ferential pion f l x is ~1/10 that of

the neutron f l x [2 ] Th s, the flu of pion in the atmosphere is so smal (<1 %) comp red to

that of the neutron , that they can b ig ored f or purp ses of eff ects on electronic The

QARM model [12] can provide detai ed flu an sp ctrum information within the atmosphere

f or these other cosmic ray secon ary p rticles, in lu in proton An ex E provides

con ideration of ef fects at hig er altitu es, a ove 6 0 0 ft (18 2 0 m)

Electron an gamma ray are also prod ced as secon ary cosmic radiation in the

atmosphere Althou h these p rticles do not have a hig enou h dE/dx (energ de osition p r

p th len th) in si con to cau e sin le event eff ects in electronic , they do de osit an ionisin

dose in the electronic In general terms, the flu es of hig energ electron an gamma ray

are rou hly comp ra le to those of the atmospheric neutron

There is also a very smal p rcentage of he v ion , i.e primary cosmic ray an their

secon ary f agments in the atmosphere that s rvive the p s age throu h the h n red of

g⋅cm

-2

of atmosphere However their flu is very low Theref ore, he v ion in the atmosphere

can b general y ig ored as a p tential thre t to electronic , althou h f or the case of very

hig altitu es it is p s ible that some he v ion may b en ou tered Only for altitu es

gre ter than 6 0 0 ft (18,3 km) may ad itional con ideration ne d to b given f or the ef fects

of he v ion [28, 2 ] as wel as for the ef fects f rom primary cosmic ray an their secon ary

f ragments At present, the QARM model [12] do s not provide inf ormation on the red ced

f l xes of primary cosmic ray he v ion an their secon ary fagments within the atmosphere

1×10–3

1×10–4

1×10–5

1×10–6

5.6 Solar e ha c me ts

Solar activity fol ows an a proximately 1 -ye r c cle, d rin whic time there are p riod of

heig tened activity (a proximately the mid le 6 ye rs) an les ened activity (a proximately

the f irst 2,5 ye rs an last 2,5 ye rs) Durin the entire p riod there is a f i ite pro a i ty of

eruption on the s n, s c as solar f lares or coronal mas ejection that res lt in energetic

p rticles b in emit ed

In general, these solar energetic p rticles have les energ than the galactic cosmic ray The

f irst p rticles re c the Earth in a mat er of min tes but the en an ements last for several

hours to day They interact with the atmosphere to cre te secon ary p rticles in a simi ar

way to galactic cosmic ray but their lower energy me n that they prod ce mu h ste p r

altitu e an latitu e profi es F r a f ew events the p rticle energies are s f ficiently hig to

give en an ed secon ary flu es at aircraft altitu es an on the grou d (so-cal ed grou d level

events or GLEs)

The en an ed secon ary cosmic ray d rin solar flares have b en me s red on the grou d

by the worldwide network of cosmic ray neutron detectors (contin al y trac in the variation of

the cosmic ray en ironment an oc asional y by in truments a o rd aircraft [3 , 31] The

SEP en an ement in the atmospheric neutron flu , relative to the b c grou d f l x (>10 MeV)

of 6 0 0 neutron⋅cm

-2

⋅h-

in 5.3.2, has b en calc lated for a n mb r of worst-case s enarios

These s enarios are de en ent on the p rticle sp ctra f rom sp cif i solar flare events, the

altitu e an the rigidity c t-of f For the Se temb r 19 9 flare, the en an ement factors at

3 0 0 f t (12 km) are 41 an 1,6 f or rigidities of 0 GV an 3 GV resp ctively, an at an

altitu e of 5 0 0 ft (17 km) the factors in re se to 7 an 2,4 resp ctively With the Fe ruary

19 6 f lare, for whic the in omin p rticle sp ctrum is les wel c aracterized, the

en an ement factor is 2 3 at 0 GV an 3 0 0 ft (12 km) Th s, extremely hig SEE rates

could oc ur in the hig latitu e region (R ≤ 1 GV) d rin worst case flares that could b

en an ed by a factor as hig as 3 0 at 3 0 0 f t (12 km) Su h very large events are termed

extreme sp ce we ther, with, typical y, en an ements of more than 10 times nominal flu es

This s bject wi b covered in more detai in a f uture new p rt of the IEC 6 3 6 series

(IEC TS 6 3 6-6)

These events are u ualy of s ort d ration (several hours) an f or worst case take-of f times

are contained within the d ration of lon haul f lig ts Hen e althou h the worst case

in tantane u rate en an ement is as hig as a f actor of 2 3 the in re sed SEE rate

averaged over a hig latitu e fl g t would b more l ke 2 times the solar minimum q iet-time

rate The QARM model in lu es seven solar p rticle events whic have b en model ed in

detai [3 ] Five of these have b en comp red f avoura ly with the lmited avaia le f lig t data

on air crew dose Use of these events in QARM ena les the worst case f lig t s enarios with

resp ct to take-of f time to b determined The F bruary 19 6 event is the worst case

avai a le, an b sed on grou d level data is the worst sin e s c monitorin commen ed in

19 2 However, b sed on the in irect eviden e of nitrate samples in ice cores, the first solar

flare ever o served ( he Car in ton event of 1 Se temb r 18 9) could have b en four times

worse [3 , 3 ] In ad ition analy is of events with resp ct to air crew dose [3 ] s ows that

four other events in the 19 0s could have ex e ded 10 times the normal f lig t-averaged dose

or SEE rate at high latitu e an 3 0 0 f t With the more recent events of 2 Se temb r 19 9

an 2 Jan ary 2 0 ( his f ortu ately only at hig southern latitu es d e to large anisotro y

in ar ival direction ) also in this category, the f req en y of s c worst case events s ould b

taken as seven in 6 ye rs Some 2 other events (e.g 15 Apri 2 01) could have given

route-averaged rates at hig latitu e ran in f rom 10 % to 2 0 % of q iet time over this time

p riod

5.7 High altitud s gre ter th n 6 0 0 f t (18 2 0 m)

Althou h neutron are the dominant cau e of SEEs up to a out 4 0 0 ft (12,2 km) other

p rticles b come in re sin ly imp rtant at hig er altitu es Proton contribute to the neutron

rate at 6 0 0 f t (18,3 km) an a ove 6 0 0 f t (18,3 km), whi e a ove this altitu e there is

sig if i ant p netration of cosmic ray he v ion an their secon ary f agments In ad ition

the imp rtan e of solar p rticle events in re ses an the Fe ruary 19 6 event would have

b en six times worse at 6 0 0 f t (18,3 km) comp red to 4 0 0 ft (12,2 km) Cur ently

models s c as QARM in lu e neutron an proton but not he v ion

He v ion prod ce SEE by direct ionization an tec niq es s c as CREME9 [3 , 3 ] are

u ed for sp ce s stems These are b sed on the c aracterisation of the en ironment by the

sp ctrum of p rticles as a f un tion of l ne r energ tran fer (LET) This is u ual y plot ed in

integral f orm, i.e the flu of p rticles havin gre ter LET The p th len th distribution throu h

a p ralele ip d re resentation of an electronic device sen itive volume is then employed to

give the sp ctrum of c arge de osition an hen e a n mb r gre ter than a device thres old

f or SEE Earler work [2 ] has presented LET sp ctra f or the up er atmosphere u in semi

-empirical cros -section for he v ion interaction an the generation of f ragments Modern

Monte Carlo radiation tran p rt codes s c as FLUKA [3 ] now contain ph sic mod les to

de l with ion-ion col sion an these are b in a pled to generate resp n e f un tion for the

atmosphere

An exes E an F give detai s of the hig altitu e en ironment an calc lation of SEE rates

prod ced by he v ion as wel as neutron an proton Fig re E.6 an Fig re E.7 can b

ef fectively u ed to estimate the SEU contribution f rom the thre p rticles (neutron ,

secon ary proton an primary cosmic ray he v ion ) within the atmosphere as a fu ction of

altitu e, b sed on the SEU resp n e of a p rtic lar SRAM From Fig re E.6 an Fig re E.7

the neutron SEU contribution is se n to decre se at altitu es ab ve 6 0 0 ft, the proton

contribution re c es a plate u at 6 0 0 ft an the he v ion contribution in re ses

sig if i antly a ove 8 0 0 ft

6 Ef f ects of atmospheric radiation on avionics

6.1 Type of ra iation ef fe ts

The ionisin radiation en ironment in the atmosphere, an theref ore within an aircraft, can

cau e a variety of ef fects on the electronic u ed in avionic Thre b sic typ s of radiation

ef fects on electronic are de lt with in Clau e 6, sin le event ef fects, total ionisin dose an

displacement damage It is s own that some sin le event ef fects have an imp ct on avionic

but that total ionisin dose an displacement damage are not of con ern Th s, the main

f oc s is on sin le event eff ects in avionic "Sin le event ef fects" is a generic term an

en omp s es al of the p tential eff ects on the electronic cau ed by the interaction of a

sin le element of adiation; in the case of atmospheric radiation, this is secon ary neutron

Out of the man typ s of p rticles res lting f rom cosmic ray cas adin throu h the Earth’s

atmosphere re c in se level, neutron are the most sig ificant in cau in electronic circ it

problems

6.2 Single e e t ef fe ts (SEEs)

Al sin le event ef fects (SEEs) are cau ed by the de osition of energy within an electronic

device by a sin le p rticle that interacts with the device The energ de osition, whic oc urs

either directly or in irectly, le d to a c arge b in col ected When the in omin p rticle is

c arged (for example, cosmic ray he v ion), the ionization proce d directly as the p rticle

de osits its energ by ionisin the s r ou din si con atoms The gre ter the a i ty of the

p rticle to rele se its energ , the gre ter the energ de osited by the p rticle (expres ed as

LET (l ne r energy tran f er), energ /p th len th), the more lkely the c arge rele sed is

s f ficient to cau e an ef fect When the sin le p rticle is neutral, s c as a neutron, the

p rticle first has to have a n cle r interaction with an atom within or ne r the active are of

the device This cre tes recoi n atoms, cal ed recoi s, whic p s es energ that is

de osited (in irectly) into the s r ou din si con atoms

A proton is c arged an has a low LET in si con but has b en s own to cau e SEE by direct

ionization in electronic devices with ge metry at an b low 9 nm However, at hig energies

(> 5 MeV), it also has n cle r re ction with si con in a man er simi ar to how a neutron of

the same energ would interact Th s to date, proton cau e sin le event ef fects in electronic

devices only throu h n cle r re ction Based on actual me s rements, we as ume that f or

energies > 10 MeV, proton an neutron have the same a i ty to in u e a sin le event

upset (SEU), a fl p in the logic state, in electronic devices This is cal ed the SEU cros

-section, an hen e, atmospheric neutron are as umed to have the same SEU cros -section

as hig energ proton

In avionic , SEEs have b en o served in electronic devices u ed in aircraft sin e the e rly

19 0s [5, 8, 3 , 4 , 41] In the existin l terature, SEUs in memory devices have b en

recorded Most if not al of the upsets have b en atributed to the atmospheric neutron As

the size of the total n mb r of bits in an aircraf t that are sen itive to SEU has in re sed

ge metrical y over the last decade (more bits p r electronic device, gre ter f un tionalty

le din to the ne d for more memory), the n mb r of SEUs b in in u ed has simi arly

in re sed However, there is not a gre t de l of doc mented eviden e of these in-f lig t SEUs

f or a variety of re son :

a) the u e of er or detection an cor ection s hemes is routinely u ed in avionic , but sin e

the er ors are cor ected, there is lt le interest in recordin the er ors that are detected an

cor ected;

b) the oc ur en e of these er ors is con idered pro rietary inf ormation, hen e it is rarely

col ected, an even les of ten analy ed; an

c) most er or cor ection s hemes lo k f or er ors only in memory that is b in uti sed, hen e

bit f lips in u u ed memory wi alway b ig ored

6.2.2 Single e e t ups t (SEU)

A sin le event upset (SEU) is the most common typ of a sin le event ef fect SEU is cau ed

by the de osition of c arge in an electronic device by a sin le p rticle that is s ff i ient to

c an e the logic state of a sin le bit f rom one binary state to the other SEUs are sometimes

cal ed sof t er ors b cau e they are re di y cor ected by reinitial sin the bits Electronic

devices sen itive to SEUs general y have b en memory bits, register bits or latc es Ran om

ac es memories are general y the most sen itive electronic devices to SEU b cau e they

contain the largest n mb r of memory bits However d e to the large n mb r of volati e

memory bits contained within micro roces or cac ed memories an registers,

microcontrol ers, ASICs an f ield programma le gate ar ay (FPGAs) are also v lnera le

SEU sen itivity in re ses as the a pl ed s p ly voltage decre ses

More recently the p tential f or SEU d e to thermal neutrons has b en o served in hig

den ity complex electronic devices that have very smal f eature size an a low critical c arge

f or upset Thermal neutron are prod ced when hig energ secon ary neutron interact with

the aircraft stru ture, in p rtic lar the h drogenou materials, f or example b g age,

p s en ers an fuel The thermal neutron flu within the aircraf t may b a out 2 times that of

the hig energy neutron at some location A thermal neutron SEU cros -section comp ra le

to that of the hig energ secon ary neutron was o served d rin the SEU testin of SRAMs

by several dif ferent groups (se 8.3.3) These electronic devices have a thermal neutron

cros -section b cau e they contain b ron 10 The comp ratively hig thermal neutron f l x

as ociated with the aircraf t en ironment me n that f or electronic devices that contain b ron

10 in an p rcentage, con ideration s al b given to the thermal neutron flu (for further

detai s refer to An ex A)

6.2.3 Multiple bit ups t (MBU) a d multiple c l ups t (MCU)

Multiple bit upset (MBU) ref ers to multiple bits (bits that are in the same logical word) b in

upset d rin the same SEE interaction MBU dif fers f om multiple cel upset (MCU) in whic

two or more bits (cel s) are upset, u ual y bits phy ical y located ne r e c other, but not

neces ari y in the same logical word The multiple cel upset (MCU) f raction (pro a i ty of

MCU/pro a i ty of SEU or MCU cros -section (multipl city > 1) SEU cros -section) in re ses

with the decre sin f eature size an with more recent IC fa rication in a dramatic way This is

b l eved to b d e to c arge s arin , i.e the c arge de osited by the energetic neutron

interactin with the SRAM is b in s ared by a n mb r of adjacent memory bits

With regard to SRAMs, those f abricated in arou d 2 0 had an MCU faction of ~ % f or

13 nm electronic devices but of ~ % for 9 nm electronic devices when tested in a

sp l ation neutron b am in Ja an [4 ] However, b sed on a later compi ation of s c data

[4 ] f rom eig t diff erent sources, in lu in referen e [4 ] the MCU f action was definitely

in reasin with decre sin fe ture size, however there a p ar to b two se arate tren lnes

For one set of electronic devices the MCU f raction starts relatively low, simi ar to ref eren e

[4 ] (~ % for 15 nm electronic devices), but in re ses by a out a f actor of 2 as the fe ture

size decre ses f rom 15 nm to 5 nm For the other set of electronic devices the MCU

f raction starts mu h hig er, for example ~ 0 % for 15 nm electronic devices, but in re ses

mu h more slowly, by a out a factor of 2 as the f eature size decre ses f om 15 nm to 5 nm

Further, more recent data has s own s bstantial y wider variation , with data p ints fal n in

b twe n the two tren l nes What is con istent with the two tren l nes is that when

extra olatin out to a f eature size of ~ 5 nm, the MCU faction wi b 1,0 i.e al SEUs wi

res lt in two or more bits b in upset

One of the recent p p rs [4 ] also in estigated the ef fect of c an in the an le of in iden e

of the neutron b am strikin the electronic device on the MCU faction The MCU f action

in reased with the an le of in iden e, it was lowest for normal in iden e an hig est for

grazin in iden e (90°), but the overal me s red in re se over normal in iden e was at most

~ 0 % at 9 ° an ~ 0 % at 4 °

The variation of the MCU f action with energy was examined [4 ] via testin with mon

o-energetic proton an the overal con lu ion is that the MCU f raction decre sed very slg tly

with decre sin energy The variation with proton energ was not u if orm, but the

a proximate decre se in the MCU f raction was f om ~ 5 % f or E = 2 0 MeV to 2 % for

E = 4 MeV f or the f irst electronic device, an f om ~18 % f or E = 2 0 MeV to ~15 % for

E = 3 MeV f or the secon device

Th s f or SRAMs, the MCU rate as a f raction of the SEU rate primari y de en s on the fe ture

size (an more cru ely the ye r of f abrication) of the electronic device, with the

neutron/proton energ havin a very smal eff ect an the an le of in iden e havin a larger

ef fect The large variation in the MCU f raction in the variou SRAMs tested by the diff erent

rese rc ers cited a ove s ould b d ly noted As a res lt, only the con ervative up er

b u d s mmarized b low can b provided f or the MCU f raction in SRAMs, an even these

are not the most con ervative values that could b u ed If these values are con idered to

hig , in ivid al zed SEE testin would b req ired to me s re the MCU f action in actual

devices

For older electronic devices, fa ricated prior to 2 0 , the g idan e in the original IEC TS

6 3 6-1:2 0 was that an MCU faction of 3 % s ould b u ed F r electronic devices

f abricated b twe n 2 0 an 2 0 , an MCU f raction of 10 % may b u ed For electronic

devices fa ricated after 2 0 an in p rtic lar for fe ture sizes of <10 nm, an up er b u d

of 3 % may b u ed

For DRAMs the situation is mu h diff erent, b cau e DRAMs contain control logic in their

p riphery Th s when this logic is upset, entire bitl nes an rows can b upset, res ltin in

thou an s of bits b in in er or d e to a sin le neutron hit Su h thou an bit er ors are

cal ed burst er ors an can often b con idered as a SEFI rather than a multiple cel upset

The MBU / MCU faction relative to SEU in re ses with in ident p rticle energ an has b en

o served to b 7 % for 6 MeV proton on 16 Mbit DRAMs Multipl cities up to 4 have b en

o served f or proton an of 19 f or ion [4 , 4 ]

Uti sin the data f om [4 ] the situation regardin MCU in DRAMs can b general zed b sed

on the f eature size, simi ar to the cru ial role played by f eature size regardin MCU in

with larger fe ture sizes, the g idan e in the original IEC TS 6 3 6-1:2 0 in icates that an

MCU f raction of 3 % s ould b u ed However, f or the 18 nm electronic devices, multi

-thou an bit upsets are p s ible, but there is wide variation in the SEFI resp n e of the two

SDR DRAMs in whic it was me s red The SEFI/SBU ration varied b twe n 0,3 % to 2 %

an the a solute cros -section varied b twe n 3,5 × 10

For 1 0 nm DRAMs, the f raction f or clas ical MCU is very u certain b cau e of the

tremen ou variation in the MCU faction, whic varies fom 2 % to 10 % in the thre

dif ferent electronic devices tested, al 512 Mbit DDR2 devices However, in terms of a solute

MCU cros -section the variation is mu h smal er, betwe n ~1 × 10

–1

cm2⋅

device-

to

3,5 × 10

–1

cm2⋅

device-

For the SEFI typ of event that res lts in 1 × 10

3

to 1 × 10

4

er one u bits, SEFI was mu h more lkely than SBU Th s, the SEFI/SBU ratio (p r device

b sis) varied b twe n ~1 to 2 , with an average value of ≈ 5, an the a solute SEFI cros

-section varied b twe n 1 × 10

–1

cm2

⋅device

-

For 9 nm DRAMs, the situation is simi ar to that of the 1 0 nm DRAMs However, only one of

the four 9 nm DDR2 devices tested ex ibited the clas ical MCU, an f or this electronic

device, the MCU f raction was 14 % Al f our DDR2 s owed the SEFI typ of resp n e of

thou an s of er ors, but in this case, SBU was more l kely than SEFI an for these four the

SEFI/SBU ratio was ~15 % The a solute SEFI cros -section varied b twe n

4 × 10

- 2

cm2

⋅device

- However, in a se arate test of DDR an

DDR2 DRAMs of 9 nm to 1 0 nm [4 ] electronic devices fom two ven ors ex ibited burst

er ors, whi e four se arate electronic devices f rom a third ven or s owed no burst er ors

Th s, the sen itivity to burst er ors varies amon DRAM ven ors, some electronic devices

b in immu e

In s mmary, it a p ars that the multi-thou an bit burst or SEFI events are more of a pro lem

than the clas ical 2-bit or 3-bit MCU, but DRAMs f om some ven ors are sen itive to the burst

er ors, thou h not f om al ven ors For electronic devices that are sen itive to burst er ors,

the overal tren in the a solute SEFI cros -section a p ars to b grad al y decre sin with

f eature size, f rom ~1 × 10

–10

cm2

⋅device

-f or 9 nm

For hig den ity memories, d e to the more complex arc itecture of p ripheral p rts/f un tion

a hig er SEFI distribution can b exp cted [5 ]

6.2.4 Single ef fe t tra sie ts (SETs)

An SEU- elated event in some electronic devices can le d to the generation of a sin le event

tran ient (SET) whic a device may interpret as a new bit of information These tran ients are

spuriou sig als or voltages, in u ed by the de osition of c arge by a sin le p rticle that

pro agates throu h the circ it p th d rin one cloc c cle These sig als may b harmful by

pro agatin to a latc an b comin f i ed, or by strikin an internal node an cau in an

u wanted resp n e or they can b eff ectively removed by the legitimate s n hronou sig als

of the circ it Initial y, s c tran ients were o served in l ne r analog e devices s c as

comp rators an o erational ampl fiers, but they have also b en recorded in digital devices

In analog e devices the SET may b manifested as a c an e in the timin of voltage or

c r ent sig als, an is de en ent on the mag itu e of the drivin dif ferential voltage Most

SET tests have b en p r ormed u in b ams of he v ion , but SET has also b en in u ed in

l ne r devices with hig -energ proton b ams [51, 5 , 5 ] hen e the atmospheric neutron

also cau e this kin of ef fect

A digital sin le event tran ient (DSET) is a spuriou digital sig al or voltage, in u ed by the

de osition of c arge by a sin le p rticle that can pro agate throu h the circ it p th d rin

one cloc c cle As the feq en y of digital electronic has risen a ove 10 MHz the p tential

f or DSET has in re sed A DSET that is cloc ed into a f lip flo or register may a p ar as an

SEU in that element

An analog e sin le event tran ient (ASET) is a spuriou sig al or voltage prod ced at the

output of an analog e device by the de osition of c arge by a sin le p rticle This er one u

output may p rsist lon enou h to provide false values to monitorin circ it elements, f or

example analog e to digital con erters, eff ectively providin cor upt data

6.2.5 Single e e t latc -up (SEL)

A sin le event latc -up (SEL) is a regenerative c r ent f low con ition in whic a p rasitic

n-p-n-p p thway in a si con electronic device is turned on by the de osition of c arge f rom a

sin le p rticle SEL has general y b en a con ern in bulk CMOS devices, but it has also b en

se n in CMOS devices with relatively thic (> 10 µm) e itaxial layers The regenerative circ it

provides a p th for large c r ent f low an can of ten le d to destru tive bre k own Even if the

bre k own do s not oc ur, the latc ed p th wi p rsist u ti p wer is removed f rom the

device, so p wer s al b rec cled to restore normal o eration Begin in in 19 2, a smal

n mb r of CMOS devices have b en s own to b sen itive to proton an neutron-in u ed

latc -up [5 , 5 ] SEL sen itivity decre ses as the a pl ed voltage decre ses, an in re ses

as the device temp rature in re ses In ad ition, on very rare oc asion , other sin le event

in u ed mec anisms have b en o served whic can le d to a hig c r ent con ition in a

device that could le d to its destru tion One s c example is a driver contention mec anism

in one typ of FPGA [5 ] other sp cial zed mec anisms have b en o served to imp ct

bip lar devices [5 , 5 ]

6.2.6 Single e e t fu ctional inter upt (SEFI)

A sin le event f un tional inter upt (SEFI) refers to an SEU in an electronic device, u ual y a

complex electronic device (f or example, a micro roces or), s c that a control p th is

cor upted, le din the device to ce se to fu ction pro erly This eff ect has sometimes b en

refer ed to as loc up, in icatin that the electronic device has b en put into a “f rozen” state

General y, SEFI is brou ht a out by an SEU in a critical bit, s c as a bit that controls

imp rtant down tre m o eration Examples of s c bits are program cou ters, sp cial

f un tion registers, control, timin an mode registers in DRAMs an even bui t-in test (BIT)

bits uti sed by the electronic device ven or only for pre-s re n testin In some electronic

devices s c as DRAMs [5 ] an FPGAs [6 ] a SEFI can le d to an in re se in the s p ly

c r ent whic is simi ar to the ef fect of a sin le event latc -up, but proce d via a dif ferent

mec anism

6.2.7 Single e e t burnout (SEB)

Electronic devices s c as N-c annel p wer MOSFETs, in ulated gate bip lar tran istors

(IGBTs) and bip lar p wer tran istors an diodes, whic have large a pl ed voltage biases

an hig internal electric f ield , are sen itive to sin le event in u ed burnout (SEB) The

p netration of the source-b dy-drain region by the c arge de osited by a he v ion can

f orward bias the thin b d region u der the source If the terminal bias a pl ed to the drain

ex e d the local bre k own voltage of the p rasitic bip lar, the sin le event in u ed pulse

initiates avalan hin in the drain de letion region that eventual y le d to destru tive burnout

In commercial N-c an el p wer MOSFETs, this eff ect can oc ur at values of the drain

voltage, V

DS, lower than the rated voltage of the electronic device Based on the res lts fom

radiation testin in a he v ion b am, a thres old V

DS

is def i ed as the hig est V

DS

at whic

the MOSFET can b o erated with no pro a i ty of SEB b in in u ed by that he v ion

Energetic neutron an proton are also a le to in u e SEB in N-c an el p wer MOSFETs

[61] In al cases, the thres old V

DS

f or neutron an proton is hig er than it is for he v

ion SEB is preclu ed by o eratin the MOSFET b low the V

at > 9 % of rated voltage) have exp rien ed

destru tive fai ures that are con istent with rates d e to SEB by the atmospheric neutron

[6 ] Sin e the atmospheric neutron flu level at aircraf t altitu es is more than 10 times

gre ter than at grou d level, the p tential for SEB in hig voltage electronic devices in

avionic is a p tential con ern L ser testin may b u ed to determine sen itivity of hig

voltage electronic devices to SEB (se B.5) The eff ects of atmospheric radiation on hig

voltage electronic an desig mitigation are detai ed in IEC 6 3 6-4

6.2.8 Single e e t gate rupture (SEGR)

Both N-c an el an P-c an el p wer MOSFETs are s bject to sin le event gate rupture

(SEGR) This eff ect is explained via the tran ient plasma fi ament cre ted by a he v ion

trac when it strikes the MOSFET throu h the thin gate oxide region As a res lt of this ion

trac fi ament, there is a localsed in re se in the oxide f ield whic can cau e oxide

break own le din first to gate le kage an final y to gate rupture With MOSFETs, grou d

level testin of hig voltage electronic devices [6 ] has s own that in some of the devices the

f ai ure was d e to SEGR, rather than SEB Th s the hig energy atmospheric neutron are

a le to in u e SEGR in some hig voltage MOSFETs

A related ef fect that has b en se n in electronic devices s c as f ield programma le gate

ar ay (FPGAs) is sin le event dielectric rupture (SEDR) in whic a thin dielectric is ruptured

by he v ion with very hig LET Testin to date has s own that the dielectric are ruptured

only by he v ion with very hig LETs, an not by energetic neutron or proton

6.2.9 Single e e t indu e hard er or (SHE)

It has lon be n k own that he v ion are a le to cau e "stu k bits" in SRAMs These events

are sometimes refer ed to as sin le hard er ors (SHEs) These hard er ors are d e to very

local sed total dose ef fects, cau ed by a f ew ion impin in on the gate oxide of sen itive

tran istors Stu k bits are sig if i ant b cau e they can in al date the most common f orm of

er or detection an cor ection (EDAC), cal ed SECDED, sin le er or cor ect, double er or

detect Stu k bits are not cor ected by EDAC so they p rsist If a word contain a stu k bit, a

sin le SEU in another bit in that word at an time then prod ces an o serva le er or In the

e rly oc ur en es of these hard er ors, the er ors were cau ed only by he v ion with hig

LET More recently the f irst oc ur en e of SHE by proton in a la oratory test was publs ed,

in icatin that in newer electronic devices (in this case a 6 Mbit DRAM, [6 ]), proton , an

hen e atmospheric neutron , are ca a le of in u in stu k bits

6.2.10 SEE pote tial ris s ba e on future te h ology

As tec nolog develo s in the f uture the imp ct of atmospheric radiation on electronic devices

wi in re se an the fol owin lst hig l g ts p tential imp ct

a) Ef fects of MBU an MCU f or f uture electronic devices of ≤ 3 nm: an MCU f raction of

10 % s ould b exp cted

The MCU rate f or SRAM devices f abricated b f ore 2 0 with f eature sizes 2 0 nm an

a ove is typical y a f ew p r cent As fe ture sizes of more recent SRAM devices have

red ced to 15 nm, the MCU rate has in re sed to a out 4 % an the exp ctation is that

for fe ture sizes of 3 nm an b low, an MCU faction of 10 % wi res lt

b) Ef fects on smal ge metry flas ROM

Traditional y the non-volati e ROM memory has b en very tolerant of the neutron in

atmospheric radiation However at fe ture sizes a pro c in an lower than 10 nm the

memories may b come sen itive to variou SEEs, in lu in SEFI

c) Direct ionization by proton is sig if i ant f or 6 nm an b low

Testin of SOI SRAMs at fe ture sizes of 9 nm an b low s ows that there is no

thres old energ for proton-in u ed upsets in some electronic devices, an the cros

-section in f act in re ses b low 1 MeV [6 , 6 ] Direct ionization by proton at hig LET

values ne r the en of the trac , as o p sed to n cle r re ction , is s f ficient to give SEU

in s c electronic devices These low energ , or sto pin , proton are generated in

materials local to the electronic device an wi ad to the SEU rates

F r electronic devices u ed in large fielded s stems s c as aircraft, the gre ter the mas

s r ou din the electronic the more u lkely that the electronic within wi b sen itive to

SEU f om direct ionization f rom external low energ proton This is b cau e the “en of

trac ” distan e within whic the hig est proton LET is ac ieved in si con (req ired to

prod ce an SEU) is 1 µm to 2 µm (~ × 10

–5

to 8 × 10

–5

in hes), comp red to the

centimetres of material that s r ou d the electronic devices, makin energ de osition

fom the proton within the sen itive 1 µm to 2 µm u lkely However the electronic

devices wi b sen itive to hig er energ proton whic wi lose energ d e to the mas

s r ou ding the electronic an then wi b in the low energ domain Ad itional y, the

electronic devices wi also b sen itive to secon ary proton generated local y in

materials s r ou din the device

d) Direct ionization by muon

Muon b have l ke electron but are 2 0 times he vier an come fom pion decay Pion

are cre ted ju t l ke neutron d rin n cle r re ction b twe n cosmic ray proton an

the ox gen an nitrogen in the atmosphere Becau e muon are we kly interactin they

do not cau e upsets by interactin with si con an so can only cau e upset throu h direct

ionization Muon are the most dominant p rticle in cosmic ray at grou d level but most

have energies of 1 0 0 MeV or hig er However some wi b prod ced at lower energy or

b degraded to lower energy For SEE f rom direct ionization to take place the muon have

to b 1 MeV or b low The imp ct of ad itional particles, f or example pion an muon , on

electronic devices with very smal ge metry, wi b covered in more detai in a pro osed

f uture new p rt of the IEC 6 3 6 series (IEC TS 6 3 6-8)

6.3 Total ionising dos (TID)

Total ionisin dose (TID) eff ects refer to the c mulative eff ect of ionization (c arge buid-up)

in an electronic device le din to a grad al degradation of electrical p rameters When a

MOS (metal oxide-semicon u tor) device is exp sed to ionising radiation, electron-hole p irs

are cre ted throu hout the oxide, in u in the bui d-up of c arge whic le d to device

degradation The main mec anisms are the bui d-up of the p sitive oxide tra c arge in the

oxide an of the interf ace-tra c arge in the inter ace b twe n the si con an the si con

dioxide L rge con entration of oxide-tra c arge cau e in re sed le kage c r ent in an

electronic device L rge con entration of interf ace-tra c arge in re se the thres old

voltage of tran istors, degradin the timin p rameters of a device Simi ar eff ects are also

cau ed in bip lar devices

Based on previou total dose testin exp rien e of electronic devices over the p st 2 ye rs,

in olvin pro a ly thou an s of diff erent devices, an eff ective lower b u d on the minimum

TID level that can cau e a device to o erate out of sp cification is 1 0 0 cGy (e.g de osited

in si con) For the vast majority of electronic devices, in lu in almost al commercial of f the

s elf (COTS) electronic devices, the TID thres old level is mu h hig er than 1 0 0 cGy

Nevertheles , u in 1 0 0 cGy as the minimum thres old, an even in lu in a factor of 2 f or

margin, this me n that a worst case minimum total dose level that aircraft avionic would

have to a sorb is 5 0 cGy b f ore TID eff ects could p s ibly b an is ue of con ern in

avionic

Al of the major p rticles that con titute the radiation en ironment within the atmosphere, i.e

neutron , proton , electron , photon , etc, contribute to the ionisin dose Based on

me s rements made in a commercial airl ner [6 ] the maximum dose rate fom al of the

this res lts in ~4 cGy of dose over that lf etime, whic is an order of mag itu e lower than

the worst case TID thres old of 5 0 cGy For aircraf t at hig er altitu es, for example 5 0 0 ft

(16,8 km), the dose rate doubles to 8 µGy⋅h

-with a maximum dose over 10 0 0 fl g t hours

of 8 cGy wel b low the TID thres old However the total ionisin dose is c mulative an any

dose f rom other sources s ould also be con idered, for example mec anical X- ay testin

An up er b u d estimate on the maximum dose that an electronic device mig t receive fom

an X- ay in p ction is 1 mGy This is extra olated f rom the maximum dose that o jects may

receive f rom X- ay mac ines u ed to in p ct lu gage (10 µGy), an is also con istent with the

a proximate ran e of doses k own to b received f om commercial X- ay in p ction s stems

(2 0 µGy to 5 0 µGy) Th s, TID eff ects are not general y an is ue for avionic

Mec anical X- ay an gamma ray in p ction is car ied out on certain p rts of the airrame to

demon trate stru tural integrity The radiation doses delvered by this typ of in p ction may

b hig er than that f om the lu gage in p ction mac ines Where s c in p ction are

car ied out if the c mulative dose received by an local sed avionic electronic eq ipment

over its lf etime in service p tential y ex e d 5 cGy, then con ideration s al b given to

removin the electronic eq ipment b fore the radiation in p ction is car ied out Examples of

s c eq ipment in lu e win an en ine mou ted electronic

6.4 Displa eme t dama e

Sti another kin of eff ect that ionisin radiation can in u e in electronic devices is

displacement damage This is also a c mulative eff ect, but in this case it refers to atoms that

are displaced out of their lat ice When a s f ficient n mb r of atoms are displaced, the

electronic device no lon er f un tion normal y This ef fect is primari y d e to the he vier

p rticles, neutron an proton , sin e l g ter p rticles, s c as electron an gamma ray ,

are mu h les ef fective in k oc in atoms out of their lat ice

Based on previou exp rien e of testin dozen of electronic devices f or displacement

damage, an eff ective lower b u d on the minimum neutron f l en e that cau es an electronic

b sed on displacement damage in sen itive o tocouplers [6 ] For electronic devices, the

neutron fluen e thres old for damage is hig er The b sis for this testin was a fluen e of

1 MeV eq ivalent neutron A large f raction of the neutron at aircraft altitu es are at hig er

energies than 1 MeV, an their p tential for cau in displacement damage in electronic

devices is gre ter than that of 1 MeV neutron The NIEL (non-ionisin energ los ) f un tion

has be n calc lated for semicon u tor materials s c as si con an gal um arsenide (GaAs)

as a f un tion of energ , an the NIEL is ac e ted as the b st me s re for the p tential of a

material to u dergo displacement damage Based on the NIEL for si con by neutron as a

f un tion of energ , it is con ervative to as ume that the hig er energ neutron have at the

most a f actor of 3 gre ter eff ectivenes in cau in displacement damage comp red to 1 MeV

of 3 as an up er b u d eq ivalen e b twe n the hig er energ neutron an the 1 MeV

neutron for purp ses of displacement damage, this f l en e con erts to a 1 MeV eq ivalent

fluen e f or avionic is sti a f actor of 4 b low the minimum level to cau e displacement

damage to the most sen itive electronic devices Hen e displacement damage is not a

pro lem for electronic devices, based on a minimum 1 MeV neutron f l en e of

Methodology an practices as ociated with safety asp cts of s stem desig can res lt in the

ac ommodation of comp nent an eq ipment soft an hard f ault rates If avionic electronic

comp nents that can exp rien e atmospheric radiation in u ed upset an fai ure ef fects

whic have the p tential to ad ersely aff ect aircraf t safety are identified, the method of

as es in the saf ety imp ct of s c ef fects is identical to that u ed to as es other p tential

hazard as ociated with an electronic avionic prod ct Fig re 6 contain a f low c art

s owin an outl ne of this proces The flowc art is con istent with the a rosp ce

recommen ed practices (ARP) contained in ARP4 5 A an ARP4 61 In ad ition to the

ARPs, q antitative req irements for the avai a i ty of aircraf t f un tion are provided in

AC2 13 9-1C an AC2 13 9-1A Ad itional g idan e f or s stem desig ers for SEE

mitigation is provided in IEC 6 3 6-3 A future new p rt of the IEC 6 3 6 series,

(IEC TS 6 3 6-7) wi ad res sp cifical y the s bject of in orp ratin atmospheric radiation

ef fects analy is into the s stem desig an re ortin proces

Figure 6 – Sy tem s fety a s s me t proc s

The f irst ste in the develo ment proces is to al ocate the aircraft level f un tion to s stems

whic wi implement these f un tion As p rt of this develo ment phase, e c of the s stems

is as es ed relatively to p tential hazard , whic could imp ct aircraf t saf ety, by u e of a

f un tional hazard as es ment (FHA) The FHA as es es al hazard again t a set of hazard

clas es simi ar to the clas es s own in Ta le 1 In ad ition to identification of to -level

s stem hazard the FHA identifies req ired hazard clas ification f or e c fu ction This

clas ification is set eq al to the hig est critical ty hazard as ociated with e c f un tion SEE

do s not general y cau e u iq e fu ction level f aiure eff ects as other hardware f ai ure modes

can cau e the same ef fects As a res lt SEE do s not ne d to b in lu ed as a se arate

hazard within the FHA

Sy tem develo ment as uran e levels refer to proces es u ed d rin s stem develo ment

(desig , implementation, verif i ation/certification, prod ction, etc.) It was de med neces ary

to foc s on the develo ment proces es f or s stems b sed up n "hig ly-integrated" or

"complex" (whose saf ety can ot b s own solely by test an whose logic is dif fic lt to

comprehen without the aid of analytical to ls) elements (primari y digital electronic

comp nents an software)

Develo ment as uran e activities s p ort s stem develo ment proces es Sy tems an items

are as ig ed "develo ment as uran e levels" b sed on fai ure con ition clas ification

as ociated with aircraf t-level fu ction implemented in the s stems an items The rigor an

arc it ect ure

Sy stem impleme tatio

Fu ctio al h z ard a aly sis

- Id ntify fu ctio al h zard clas es

Prelmin ry syst em safety as es me t

- Id ntify HW/SW h zard c las es

- Id ntify safety re uireme ts

Sy st em safet y as es me t

- V erify sy stem me ts safet y re uireme t s