- Email: [email protected]
Study of radiation effects of heavy ions in microelectronic devices
Nucl. Tracks Radiat. Meas., Vo[. 19, Nos 1-4, pp. 891-894, 1991 Int. J. Radial. Appl. Instrum., Part D
Printed in Great Britain
0735-245")(/91 $3.00+ .00 Pergamon Press plc
STUDY OF RADIATION E F F E C T S OF HEAVY IONS IN M I C R O E L E C T R O N I C D E V I C E S
O. Geschke i, H. Ri~cherj, A. NollI, J. Dreute t, B. Wie~el l, S. Hirzehruch l, ~vV. HeinrichI, R. Harboe Sorensen 2, L. A d a m s , J. Vetter 3 I University of Siegen, Department of Physics , P.O.Box 101240, 5900 Siegen, F.R. Germany 2 European Space Research and Technology Centre, Noordwijk, The Netherlands 3 Gesellschaft flir Schwerionenforschung, 6100 Darmstadt If, F.R. Germany
ABSTRACT W e s t a r t e d a r e s e a r c h p r o g r a m u s i n g h e a v y ion b e a m s at t h e GSI D a r m s t a d t a c c e l e r a t o r to i n v e s t i g a t e r a d i a t i o n e f f e c t s of h e a v y ions in m i c r o e l e c t r o n i c d e v i c e s . The u n d e r s t a n d i n g of t h e s e r a d i a t i o n e f f e c t s is of p a r t i c u l a r i m p o r t a n c e to e s t i m a t e t h e r a d i a t i o n risc for m i c r o e l e c t r o n i c p a r t s e x p o s e d to t h e c o s m i c r a d i a t i o n during s p a c e m i s s i o n s . In o r d e r to e x p o s e s t a t i c RAM d e v i c e s to h e a v y ion b e a m s a t e s t s y s t e m w a s i n s t a l l e d . A d d i t i o n a l l y we use CCD i m a g e s e n s o r s to m e a s u r e t h e a m o u n t of c h a r g e d e p o s i t e d inside the s e n s i t i v e v o l u m e of single p i c t u r e e l e m e n t s . M e a s u r e m e n t s will be p e r f o r m e d w i t h ions of d i f f e r e n t c h a r g e and e n e r g y up to I G e V / N to i n v e s t i g a t e t h e LET d e p e n d e n c e of t h e e f f e c t s and p o s s i b l e i n f l u e n c e of t h e t r a c k s t r u c t u r e . The e x p e r i m e n t a l s e t u p is d e s c r i b e d in t h i s p a p e r and f i r s t r e s u l t s are p r e s e n t e d .
KEYWORDS m i c r o e l e c t r o n i c d e v i c e s , r a d i a t i o n e f f e c t s , c o s m i c r a y s , s i n g l e e v e n t u p s e t , LET
INTRODUCTION In a n u m b e r of space missions i t has been observed t h a t a single cosmic ray p a r t i c l e can cause m a l f u n c t i o n of a m i c r o e l e c t r o n i c d e v i c e ( B l a k e e~t aJ., 1986). This phenomenon is c a l l e d a single e v e n t upset (SEU) (Robinson jr. et a L , 1990) , (Price et aJ., 1989). I t happens when a heavy ion deposits enough charge in the s e n s i t i v e r e g i o n to change the l o g i c a l s t a t e . I f a device, i r r a d i a t e d for t seconds w i t h a c o n s t a n t p a r t i c l e f l u x of F p a r t i c l e s 2 p e r cm 2 and sec shows a number of N SEUs the d e v i c e cross s e c t i o n is d e f i n e d as o = N / ( F ~ t ) cm . In a zero order a p p r o x i m a t i o n i t can be e x p e c t e d t h a t o is r e l a t e d to the g e o m e t r y of the s e n s i t i v e components in the d e v i c e and t h e i r t o t a l number. The cross s e c t i o n as a f u n c t i o n of L E T should be a step f u n c t i o n w i t h a step at a c r i t i c a l L E T v a l u e c o r r e s p o n d i n g to a c r i t i c a l amount of charge t h a t has to be deposited in a single s e n s i t i v e v o l u m e of a c o m p o n e n t to cause a b i t - f l i p . E x p e r i m e n t s have shown t h a t the measured cross sections increase f r o m zero at l o w L E T - v a l u e s to a s a t u r a t i o n v a l u e at high LETs w h i c h is c o m p a r a b l e to the g e o m e t r i c cross s e c t i o n of the s e n s i t i v e v o l u m e . In f a c t the cross s e c t i o n is not a single step f u n c t i o n but rises o v e r an i n t e r v a l of L E T values. I f this L E T dependent cross s e c t i o n curve is d e t e r m i n e d e x p e r i m e n t a l l y i t can be used to c a l c u l a t e the e x p e c t e d r a t e of single e v e n t upsets f o r a specific d e v i c e f l o w n in a specific space mission based on the f l u x of cosmic ray n u c l e i as a f u n c t i o n of L E T , the so c a l l e d cosmic ray L E T spectrum for this mission. L E T dependent cross sections f o r m a n y devices have been measured in the past ( B l a k e et al., 1986).For this purpose d i f f e r e n t v a l u e s of L E T are needed. T h a t means t h a t heavy ions of d i f f e r e n t energy and charge are r e q u i r e d . Since t h i s - i e q u i r e m e n t c a n n o t he f u i l f i l l e d in many e x p e r i m e n t s the p r o b l e m has been s o l v e d by t i l t i n g the devices against the beam a x i s by an angle co. For a s e n s i t i v e v o l u m e o f depth d the charge d e p o s i t e d w o u l d increase by a f a c t o r of l/cosct w h i c h corresponds to an e f f e c t i v e L E T v a l u e of LET/cos0~. This p r o c e d u r e c o m p l e t e l y neglects any e f f e c t s of the t r a c k s t r u c t u r e , energy and a n g u l a r d i s t r i b u t i o n s o f ~ - e l e c t r o n s produced by i o n i z a t i o n and therefore should only a p p r o x i m a t e l y be c o r r e c t . F u r t h e r m o r e most i n v e s t i g a t i o n s are p e r f o r m e d 891
892
O. G E S C H K E et al.
u s i n g ions of low e n e r g i e s , i.e. e n e r g i e s of only a f e w M e V / N . For t h e s e ions t h e L E T is c h a n g i n g a l o n g t h e p a t h of t h e p a r t i c l e a n d is t h e r e f o r e not c o n s t a n t o v e r t h e s e n s i t i v e v o l u m e , E x p e r i m e n t s u s i n g h e a v y ion b e a m s of r e l a t i v i s t i c e n e r g i e s o v e r c o m e m a n y of t h e s e p r o b l e m s s i n c e for t h e s e p a r t i c l e s t h e L E T is c o n s t a n t o v e r r a n g e s l a r g e r by o r d e r s of m a g n i t u d e c o m p a r e d to t h e d e p t h of t h e s e n s i t i v e v o l u m e s . In e x p e r i m e n t s u s i n g r e l a t i v i s t i c h e a v y ion b e a m s in p r i n c i p l e it is not n e c e s s a r y to open t h e d e v i c e s and to i r r a d i a t e t h e m f r o m t h e s u r f a c e side. T h e d e v i c e s c a n b e t e s t e d u n d e r c o n d i t i o n s t h a t are c o m p a r a b l e to t h e r e a l o p e r a t i o n a l c o n d i t i o n s in s p a c e . F o r L E T v a l u e s w h e r e t h e c r o s s s e c t i o n c u r v e h a s n o t r e a c h e d i t s s a t u r a t i o n v a l u e t h e p r o b a b i l i t y for an u p s e t is g i v e n by t h e r a t i o b e t w e e n t h e m e a s u r e d c r o s s s e c t i o n and t h e s a t u r a t i o n c r o s s s e c t i o n . F o r a m o r e d e t a i l e d u n d e r s t a n d i n g of t h e g e n e r a t i o n of S E U s it m a y be v e r y i m p o r t a n t to u n d e r s t a n d t h i s p r o b a b i l i t y as a r e s u l t of f l u c t u a t i o n s of t h e a m o u n t of d e p o s i t e d c h a r g e . To m e a s u r e t h e a m o u n t of c h a r g e d e p o s i t e d in a s e n s i t i v e v o l u m e we i n c l u d e d CCD i m a g e s e n s o r s as t e s t devices. EXPERIMENTAL
SETUP
W e d e v e l o p e d a t e s t s y s t e m w h i c h is a b l e to t e s t RAM c h i p s and CCD i m a g e s e n s o r s . T h e m e m o r i e s e x p o s e d to h e a v y ions c a n be l o a d e d w i t h d i f f e r e n t b i t p a t t e r n s . E r r o r s c a u s e d by h e a v y ions p e n e t r a t i n g t h e RAM are i d e n t i f i e d and l o c a l i z e d by a t e s t s o f t w a r e r u n n i n g on a m i c r o p r o c e s s o r t h a t c o n t r o l s t h i s RAM. To m e a s u r e t h e c h a r g e d e p o s i t e d i n s i d e a s i n g l e p i x e l e l e m e n t of a C C D s e n s o r , t h e i m a g e s e e n during t h e e x p o s u r e to a h e a v y ion b e a m is d i g i t i z e d i n t o e i g h t b i t g r e y l e v e l a n d w r i t t e n into t h e m e m o r y of a p i c t u r e a n a l y s i s s y s t e m . S o f t w a r e r u n n i n g on t h i s s y s t e m a l l o w s to i d e n t i f y p i x e l s t h a t h a v e b e e n h i t a n d to r e a d out t h e g r e y l e v e l w h i c h is p r o p o r t i o n a l to t h e c h a r g e d e p o s i t e d by t h e i o n i z i n g p a r t i c l e . T h e e x p e r i m e n t a l s e t u p also a l l o w s to t i l t t h e d e v i c e s a g a i n s t t h e b e a m a x i s and to o p e r a t e t h e d e v i c e s u n d e r a c o n t r o l l e d t e m p e r a t u r e . A s e t u p for m o n i t o r i n g h e a v y ion f l u x e s d u r i n g t h e e x p o s u r e s b a s e d on PIN d i o d e s w a s i n s t a l l e d . A d d i t i o n a l l y solid s t a t e n u c l e a r t r a c k d e t e c t o r s are u s e d for an a b s o l u t e c a l i b r a t i o n of p a r t i c l e f l u x e s . Fig. 1 s h o w s a s c h e m a t i c view of t h e c o n f i g u r a t i o n of t h e t e s t s y s t e m for SRAMs as it was i n s t a l l e d . &80H pPS stepping Motor control unit
Y-stepping motor
COH2
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targetboard
/ I~-PC
tenperature control unit
Move/rotate device
Fig. 1. S c h e m a t i c v i e w of t h e RAM t e s t s y s t e m c o n f i g u r a t i o n T h e s y s t e m c o n s i s t s of t h e f o l l o w i n g c o m p o n e n t s : - a h o s t c o m p u t e r ( I B M - A T ) u s e d as a c o n t r o l l e r and f i l e s e r v e r . - a m i c r o p r o c e s s o r (MC 68000) b a s e d m e m o r y t e s t s y s t e m i n c l u d i n g i n t e r f a c e s , a h a r d w a r e c o u n t e r , i n t e r n a l m e m o r y and an e x t e r n a l m e m o r y b o a r d c a l l e d t a r g e t b o a r d . - a s t e p p i n g m o t o r c o n t r o l u n i t (MC 68008) to m o v e a n d r o t a t e t h e t a r g e t b o a r d . - a t e m p e r a t u r e c o n t r o l unit to h e a t up t h e d e v i c e s to be t e s t e d . - P I N d i o d e s and a p r e a m p l i f i e r for o n l i n e m e a s u r e m e n t of t h e b e a m i n t e n s i t y . - a MC 68020 b a s e d i m a g e p r o c e s s i n g c o m p u t e r ( I P C ) to o p e r a t e CCD i m a g e s e n s o r s . T E S T OF E X P E R I M E N T A L
S E T U P AND F I R S T R E S U L T S
B e f o r e t h e e x p e r i m e n t a l s e t u p w a s b r o u g h t to GSI f i r s t t e s t s w e r e p e r f o r m e d at t h e U n i v e r s i t y of
HEAVY ION RADIATION EFFECTS
893
S i e g e n using f i s s i o n p a r t i c l e s of a C f s o u r c e . SEU c r o s s s e c t i o n s for H M I - 6 5 1 6 2 - 2 2kogBit SRAM w e r e m e a s u r e d to be 0ct, = 2.62-10-2cm 2. This n u m b e r a g r e e s w i t h t h e value o f 0av = 2.41oi0 -2 cm 2 d e t e r m i n e d at E S T E C w i t h a s i m i l a r p r o c e d u r e as an a v e r a g e v a l u e for t h r e e d e v i c e s o f t h i s t y p e . During t h e p h a s e of t h e d e v e l o p m e n t o f t h e s y s t e m s e v e n d i f f e r e n t ion b e a m s at GSI in D a r m s t a d t h a v e b e e n u s e d to p e r f o r m t e s t s of t h e e x p e r i m e n t a l s e t u p . In t h e low e n e r g y runs t h e d e v i c e s w e r e e x p o s e d to a b e a m of ions e x t r a c t e d t h r o u g h a thin 13.4 tim t i t a n w i n d o w . A f t e r p a s s i n g t h r o u g h a b o u t 6 cm of air the ions hit t h e m i e r o e l e c t r o n i c d e v i c e s w i t h a r e d u c e d e n e r g y g i v e n in T a b l e 1. The L E T and t h e r a n g e o f t h e p a r t i c l e s in s i l i c o n e q u i v a l e n t to t h i s e n e r g y is also given in T a b l e 1. For d e v i c e s e x p o s e d w i t h i n c i d e n t a n g l e s not e q u a l to z e r o t h e e f f e c t i v e LET/cosc~ is g i v e n . For t h e high e n e r g y runs w i t h Ne and Au also e x t r a c t e d b e a m s in air w e r e u s e d . The e n e r g y l o s s o f t h e s e p a r t i c l e s in t h e air can be n e g l e c t e d . The L E T v a l u e and r a n g e given for t h e s e p a r t i c l e s w a s d e t e r m i n e d for t h e b e a m e n e r g y . T a b l e 1. L i s t of e x p o s u r e s with d i f f e r e n t ion b e a m s , t h e p a r t i c l e e n e r g y in t h e b e a m p i p e , e n e r g y , c a l c u l a t e d e n e r g y loss on d e v i c e s u r f a c e , t h e r a n g e o f t h e p a r t i c l e s in t h e d e v i c e and t h e p r e l i m i n a r y r e s u l t s for c r o s s s e c t i o n s of H a r r i s H M I - 6 5 1 6 2 - 2 2 k o g b i t SRAM ion
20Ne 20Ne 20Ne 40Ar 40Ar 40Ar 40Ar 40Ar 40At 197Au 251Cf 131Xe 197Au
incident angle
beam energy
e n e r g y on surface
degrees
MeV/N
MeV/N
0 0 45 0 25 34 40 45 0 0
350, 0 11, 4 11, 4 15, 5 15, 5 15, 5 15, 5 15, 5 11,4 600, 0
0 0
11, 6 15,9
350, 9, 9, 12, 12, 12, 12, 12, 7, 386,
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e f f e c t i v e LET on s u r f a c e
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0 1 1 7 7 7 7 7 ! 5
70350 143 143 178 178 178 178 178 94 15000
5, 5 9,9
54 102
265 3667 5134 8532 9385 10238 11092 11945 11306 11949 40000 62000 89600
cross section
cm 2 ..... 1,1" 10 -5 2, 2. I0 - 5 3, 8" 10 - 3 7, 0" 10 -3 7, 6" 10 -3 9 , 6 " 10 - 3 8, 5" 10 -3 9, 5" 10 - 3 9, 8" 10 -3 2, 6" 10 -2 9, 1" 10 -2 1,9" 10 -1
Due to p r o b l e m s of a c c u r a t e b e a m flux m e a s u r e m e n t s it w a s only p o s s i b l e to get p r e l i m i n a r y r e s u l t s for t h e c r o s s s e c t i o n of t h e H M I - 6 5 1 6 2 - 2 d e v i c e for t h e d i f f e r e n t e x p o s u r e s . The b e a m m o n i t o r u s i n g PIN d i o d e s w h i c h will be u s e d in f u t u r e w a s not a v a i l a b l e during all t h e s e runs. P a r t i c l e f l u x e s had to be e s t i m a t e d b a s e d on n u c l e a r t r a c k d e t e c t o r s or on c o u n t s of not p e r f e c t l y c a l i b r a t e d PIN d i o d e s . T h e r e f o r e t h e m e a s u r e d c r o s s s e c t i o n s may have e r r o r s s i g n i f i c a n t l y l a r g e r than the s t a t i s t i c a l e r r o r r e s u l t i n g from the n u m b e r of u p s e t s o b s e r v e d . The s t a t i s t i c a l e r r o r s t y p i c a l l y r a n g e f r o m 5 to 10 p e r c e n t . In Fig. 2 c r o s s s e c t i o n s o f T a b l e 1 are p r e s e n t e d as a f u n c t i o n of LET. For t h e 11.6 M e V / N Xe and the 16 M e V / N Au e x p o s u r e s t h e m e a s u r e d c r o s s s e c t i o n s are s i g n i f i c a n t l y l a r g e r t h a n t h o s e for f i s s i o n p r o d u c t s of Cf. W e are c o n v i n c e d t h a t t h e s e r e s u l t s are not c a u s e d by u n c e r t a i n t i e s in b e a m flux c a l i b r a t i o n but o r i g i n a t e f r o m the f a c t t h a t a single ion can c a u s e m u l t i p l e b i t - f l i p s as it w a s o b s e r v e d b e f o r e ( M a r t i n et a l . , 1987) . In Fig. 3a and 3b t h e d i s t r i b u tions o f t h e n u m b e r of c o r r e l a t e d b i t - f l i p s c a u s e d by a s i n g l e p a r t i c l e are shown. For Xe a m e a n value o f 1.8 b i t - f l i p s p e r ion and for Au a m e a n value o f 2.2 b i t - f l i p s p e r ion w e r e o b s e r v e d . This m e a n s t h a t in t h e s e c a s e s the a r e a of p o t e n t i a l d a m a g e a r o u n d t h e t r a j e c t o r y is s i g n i f i c a n t l y l a r g e r t h a n t h e s i z e of a single s e n s i t i v e v o l u m e . B i t - f l i p s also can o c c u r e w h e n ions p a s s t h r o u g h i n s e n s i t i v e e l e m e n t s . This i n t e r e s t i n g p h e n o m e n o n is not d e s c r i b e d c o r r e c t l y by a c r o s s s e c t i o n of t h e form o = N/(F~,t) cm 2 with N = n u m b e r o f b i t - f l i p s o b s e r v e d . T h e r e f o r e t h e s e c r o s s s e c t i o n s w e r e n o t p r e s e n t e d in Fig. 2. N e v e r t h e l e s s a more d e t a i l e d s t u d y o f this phenomenon would be o f particular interest. For t h e 350 M e V / N Ne no s i g n i f i c a n t n u m b e r of S E U s was o b s e r v e d s i n c e on t h e one hand t h e e n e r g y loss by i o n i z a t i o n in t h e s e n s i t i v e l a y e r was too s m a l l and on t h e o t h e r h a n d t h e t e s t p e r i o d w a s not long e n o u g h to o b s e r v e t h e r a r e S E U s c a u s e d by the high a m o u n t of e n e r g y d e p o s i t e d by n u c l e a r i n t e r a c t i o n s of t h e Ne w i t h Si i n s i d e t h e d e v i c e . Our f i r s t p r e l i m i n a r y r e s u l t s are i m p o r t a n t for the p l a n n i n g o f f u t u r e t e s t s at t h e n e w SIS f a c i l i t y
894
O. G E S C H K E et al.
at GSI in D a r m s t a d t . F r o m t h e r e s u l t s of t h e f i r s t e x p o s u r e s s h o w n in Fig. 2 it c a n be c o n c l u d e d t h a t I G e V / N ions h e a v i e r t h a n X e s h o u l d b e u s e d for t h e p l a n n e d i n v e s t i g a t i o n s at t h e SIS to s t u d y t h e r i s e of t h e c r o s s s e c t i o n c u r v e s . R e l a t i v i s t i c u r a n i u m ions a p p r o a c h t h e L E T r e g i m e w h e r e t h e c r o s s s e c t i o n c u r v e is e x p e c t e d to s a t u r a t e . U s i n g d i f f e r e n t ions w i t h d i f f e r e n t e n e r g i e s b e t w e e n s o m e h u n d r e d M e V / N a n d t h e m a x i m u m GSI e n e r g y for h e a v y ions of I G e V / N t h e t o t a l L E T regime of interest can be covered. 1 0- ~ :
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REFERENCES J . B . B l a k e , R . M a n d e l , On O r b i t O b s e r v a t i o n s Of S i n g l e E v e n t U p s e t .... I E E E T r a n s . Nucl. S c i e n c e , Vol. N S - 3 3 , No. 6, (1986) R . C . M a r t i n , N . M . G h o n i e m , T h e S i z e E f f e c t Of Ion C h a r g e T r a c k s .... I E E E T r a n s . Nucl. S c i e n c e , Vol. N S - 3 4 , (1987), P a g e 1305-1309 ~,V.E.Price, J . R . C o s s , S i n g l e E v e n t P h e n o m e n a : A S u m m a r y , N u c l . ]Instr. M e t h . , B 4 0 / 4 1 (1989), P a g e 1306-1309 P . A . R o b i n s o n jr. 1 r e . L e e , R . A g u e r o , S . B . G a b r i e i , A n o m a l i e s Due To S i n g l e E v e n t U p s e t s , A[AA 9 0 - 0 1 7 4 . 28 t n A e r o s o a c e S c i e n c e s M e e t i n g . J a n . 8-11, 1990, R e n o , N e v a d a
Printed in Great Britain
0735-245")(/91 $3.00+ .00 Pergamon Press plc
STUDY OF RADIATION E F F E C T S OF HEAVY IONS IN M I C R O E L E C T R O N I C D E V I C E S
O. Geschke i, H. Ri~cherj, A. NollI, J. Dreute t, B. Wie~el l, S. Hirzehruch l, ~vV. HeinrichI, R. Harboe Sorensen 2, L. A d a m s , J. Vetter 3 I University of Siegen, Department of Physics , P.O.Box 101240, 5900 Siegen, F.R. Germany 2 European Space Research and Technology Centre, Noordwijk, The Netherlands 3 Gesellschaft flir Schwerionenforschung, 6100 Darmstadt If, F.R. Germany
ABSTRACT W e s t a r t e d a r e s e a r c h p r o g r a m u s i n g h e a v y ion b e a m s at t h e GSI D a r m s t a d t a c c e l e r a t o r to i n v e s t i g a t e r a d i a t i o n e f f e c t s of h e a v y ions in m i c r o e l e c t r o n i c d e v i c e s . The u n d e r s t a n d i n g of t h e s e r a d i a t i o n e f f e c t s is of p a r t i c u l a r i m p o r t a n c e to e s t i m a t e t h e r a d i a t i o n risc for m i c r o e l e c t r o n i c p a r t s e x p o s e d to t h e c o s m i c r a d i a t i o n during s p a c e m i s s i o n s . In o r d e r to e x p o s e s t a t i c RAM d e v i c e s to h e a v y ion b e a m s a t e s t s y s t e m w a s i n s t a l l e d . A d d i t i o n a l l y we use CCD i m a g e s e n s o r s to m e a s u r e t h e a m o u n t of c h a r g e d e p o s i t e d inside the s e n s i t i v e v o l u m e of single p i c t u r e e l e m e n t s . M e a s u r e m e n t s will be p e r f o r m e d w i t h ions of d i f f e r e n t c h a r g e and e n e r g y up to I G e V / N to i n v e s t i g a t e t h e LET d e p e n d e n c e of t h e e f f e c t s and p o s s i b l e i n f l u e n c e of t h e t r a c k s t r u c t u r e . The e x p e r i m e n t a l s e t u p is d e s c r i b e d in t h i s p a p e r and f i r s t r e s u l t s are p r e s e n t e d .
KEYWORDS m i c r o e l e c t r o n i c d e v i c e s , r a d i a t i o n e f f e c t s , c o s m i c r a y s , s i n g l e e v e n t u p s e t , LET
INTRODUCTION In a n u m b e r of space missions i t has been observed t h a t a single cosmic ray p a r t i c l e can cause m a l f u n c t i o n of a m i c r o e l e c t r o n i c d e v i c e ( B l a k e e~t aJ., 1986). This phenomenon is c a l l e d a single e v e n t upset (SEU) (Robinson jr. et a L , 1990) , (Price et aJ., 1989). I t happens when a heavy ion deposits enough charge in the s e n s i t i v e r e g i o n to change the l o g i c a l s t a t e . I f a device, i r r a d i a t e d for t seconds w i t h a c o n s t a n t p a r t i c l e f l u x of F p a r t i c l e s 2 p e r cm 2 and sec shows a number of N SEUs the d e v i c e cross s e c t i o n is d e f i n e d as o = N / ( F ~ t ) cm . In a zero order a p p r o x i m a t i o n i t can be e x p e c t e d t h a t o is r e l a t e d to the g e o m e t r y of the s e n s i t i v e components in the d e v i c e and t h e i r t o t a l number. The cross s e c t i o n as a f u n c t i o n of L E T should be a step f u n c t i o n w i t h a step at a c r i t i c a l L E T v a l u e c o r r e s p o n d i n g to a c r i t i c a l amount of charge t h a t has to be deposited in a single s e n s i t i v e v o l u m e of a c o m p o n e n t to cause a b i t - f l i p . E x p e r i m e n t s have shown t h a t the measured cross sections increase f r o m zero at l o w L E T - v a l u e s to a s a t u r a t i o n v a l u e at high LETs w h i c h is c o m p a r a b l e to the g e o m e t r i c cross s e c t i o n of the s e n s i t i v e v o l u m e . In f a c t the cross s e c t i o n is not a single step f u n c t i o n but rises o v e r an i n t e r v a l of L E T values. I f this L E T dependent cross s e c t i o n curve is d e t e r m i n e d e x p e r i m e n t a l l y i t can be used to c a l c u l a t e the e x p e c t e d r a t e of single e v e n t upsets f o r a specific d e v i c e f l o w n in a specific space mission based on the f l u x of cosmic ray n u c l e i as a f u n c t i o n of L E T , the so c a l l e d cosmic ray L E T spectrum for this mission. L E T dependent cross sections f o r m a n y devices have been measured in the past ( B l a k e et al., 1986).For this purpose d i f f e r e n t v a l u e s of L E T are needed. T h a t means t h a t heavy ions of d i f f e r e n t energy and charge are r e q u i r e d . Since t h i s - i e q u i r e m e n t c a n n o t he f u i l f i l l e d in many e x p e r i m e n t s the p r o b l e m has been s o l v e d by t i l t i n g the devices against the beam a x i s by an angle co. For a s e n s i t i v e v o l u m e o f depth d the charge d e p o s i t e d w o u l d increase by a f a c t o r of l/cosct w h i c h corresponds to an e f f e c t i v e L E T v a l u e of LET/cos0~. This p r o c e d u r e c o m p l e t e l y neglects any e f f e c t s of the t r a c k s t r u c t u r e , energy and a n g u l a r d i s t r i b u t i o n s o f ~ - e l e c t r o n s produced by i o n i z a t i o n and therefore should only a p p r o x i m a t e l y be c o r r e c t . F u r t h e r m o r e most i n v e s t i g a t i o n s are p e r f o r m e d 891
892
O. G E S C H K E et al.
u s i n g ions of low e n e r g i e s , i.e. e n e r g i e s of only a f e w M e V / N . For t h e s e ions t h e L E T is c h a n g i n g a l o n g t h e p a t h of t h e p a r t i c l e a n d is t h e r e f o r e not c o n s t a n t o v e r t h e s e n s i t i v e v o l u m e , E x p e r i m e n t s u s i n g h e a v y ion b e a m s of r e l a t i v i s t i c e n e r g i e s o v e r c o m e m a n y of t h e s e p r o b l e m s s i n c e for t h e s e p a r t i c l e s t h e L E T is c o n s t a n t o v e r r a n g e s l a r g e r by o r d e r s of m a g n i t u d e c o m p a r e d to t h e d e p t h of t h e s e n s i t i v e v o l u m e s . In e x p e r i m e n t s u s i n g r e l a t i v i s t i c h e a v y ion b e a m s in p r i n c i p l e it is not n e c e s s a r y to open t h e d e v i c e s and to i r r a d i a t e t h e m f r o m t h e s u r f a c e side. T h e d e v i c e s c a n b e t e s t e d u n d e r c o n d i t i o n s t h a t are c o m p a r a b l e to t h e r e a l o p e r a t i o n a l c o n d i t i o n s in s p a c e . F o r L E T v a l u e s w h e r e t h e c r o s s s e c t i o n c u r v e h a s n o t r e a c h e d i t s s a t u r a t i o n v a l u e t h e p r o b a b i l i t y for an u p s e t is g i v e n by t h e r a t i o b e t w e e n t h e m e a s u r e d c r o s s s e c t i o n and t h e s a t u r a t i o n c r o s s s e c t i o n . F o r a m o r e d e t a i l e d u n d e r s t a n d i n g of t h e g e n e r a t i o n of S E U s it m a y be v e r y i m p o r t a n t to u n d e r s t a n d t h i s p r o b a b i l i t y as a r e s u l t of f l u c t u a t i o n s of t h e a m o u n t of d e p o s i t e d c h a r g e . To m e a s u r e t h e a m o u n t of c h a r g e d e p o s i t e d in a s e n s i t i v e v o l u m e we i n c l u d e d CCD i m a g e s e n s o r s as t e s t devices. EXPERIMENTAL
SETUP
W e d e v e l o p e d a t e s t s y s t e m w h i c h is a b l e to t e s t RAM c h i p s and CCD i m a g e s e n s o r s . T h e m e m o r i e s e x p o s e d to h e a v y ions c a n be l o a d e d w i t h d i f f e r e n t b i t p a t t e r n s . E r r o r s c a u s e d by h e a v y ions p e n e t r a t i n g t h e RAM are i d e n t i f i e d and l o c a l i z e d by a t e s t s o f t w a r e r u n n i n g on a m i c r o p r o c e s s o r t h a t c o n t r o l s t h i s RAM. To m e a s u r e t h e c h a r g e d e p o s i t e d i n s i d e a s i n g l e p i x e l e l e m e n t of a C C D s e n s o r , t h e i m a g e s e e n during t h e e x p o s u r e to a h e a v y ion b e a m is d i g i t i z e d i n t o e i g h t b i t g r e y l e v e l a n d w r i t t e n into t h e m e m o r y of a p i c t u r e a n a l y s i s s y s t e m . S o f t w a r e r u n n i n g on t h i s s y s t e m a l l o w s to i d e n t i f y p i x e l s t h a t h a v e b e e n h i t a n d to r e a d out t h e g r e y l e v e l w h i c h is p r o p o r t i o n a l to t h e c h a r g e d e p o s i t e d by t h e i o n i z i n g p a r t i c l e . T h e e x p e r i m e n t a l s e t u p also a l l o w s to t i l t t h e d e v i c e s a g a i n s t t h e b e a m a x i s and to o p e r a t e t h e d e v i c e s u n d e r a c o n t r o l l e d t e m p e r a t u r e . A s e t u p for m o n i t o r i n g h e a v y ion f l u x e s d u r i n g t h e e x p o s u r e s b a s e d on PIN d i o d e s w a s i n s t a l l e d . A d d i t i o n a l l y solid s t a t e n u c l e a r t r a c k d e t e c t o r s are u s e d for an a b s o l u t e c a l i b r a t i o n of p a r t i c l e f l u x e s . Fig. 1 s h o w s a s c h e m a t i c view of t h e c o n f i g u r a t i o n of t h e t e s t s y s t e m for SRAMs as it was i n s t a l l e d . &80H pPS stepping Motor control unit
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Fig. 1. S c h e m a t i c v i e w of t h e RAM t e s t s y s t e m c o n f i g u r a t i o n T h e s y s t e m c o n s i s t s of t h e f o l l o w i n g c o m p o n e n t s : - a h o s t c o m p u t e r ( I B M - A T ) u s e d as a c o n t r o l l e r and f i l e s e r v e r . - a m i c r o p r o c e s s o r (MC 68000) b a s e d m e m o r y t e s t s y s t e m i n c l u d i n g i n t e r f a c e s , a h a r d w a r e c o u n t e r , i n t e r n a l m e m o r y and an e x t e r n a l m e m o r y b o a r d c a l l e d t a r g e t b o a r d . - a s t e p p i n g m o t o r c o n t r o l u n i t (MC 68008) to m o v e a n d r o t a t e t h e t a r g e t b o a r d . - a t e m p e r a t u r e c o n t r o l unit to h e a t up t h e d e v i c e s to be t e s t e d . - P I N d i o d e s and a p r e a m p l i f i e r for o n l i n e m e a s u r e m e n t of t h e b e a m i n t e n s i t y . - a MC 68020 b a s e d i m a g e p r o c e s s i n g c o m p u t e r ( I P C ) to o p e r a t e CCD i m a g e s e n s o r s . T E S T OF E X P E R I M E N T A L
S E T U P AND F I R S T R E S U L T S
B e f o r e t h e e x p e r i m e n t a l s e t u p w a s b r o u g h t to GSI f i r s t t e s t s w e r e p e r f o r m e d at t h e U n i v e r s i t y of
HEAVY ION RADIATION EFFECTS
893
S i e g e n using f i s s i o n p a r t i c l e s of a C f s o u r c e . SEU c r o s s s e c t i o n s for H M I - 6 5 1 6 2 - 2 2kogBit SRAM w e r e m e a s u r e d to be 0ct, = 2.62-10-2cm 2. This n u m b e r a g r e e s w i t h t h e value o f 0av = 2.41oi0 -2 cm 2 d e t e r m i n e d at E S T E C w i t h a s i m i l a r p r o c e d u r e as an a v e r a g e v a l u e for t h r e e d e v i c e s o f t h i s t y p e . During t h e p h a s e of t h e d e v e l o p m e n t o f t h e s y s t e m s e v e n d i f f e r e n t ion b e a m s at GSI in D a r m s t a d t h a v e b e e n u s e d to p e r f o r m t e s t s of t h e e x p e r i m e n t a l s e t u p . In t h e low e n e r g y runs t h e d e v i c e s w e r e e x p o s e d to a b e a m of ions e x t r a c t e d t h r o u g h a thin 13.4 tim t i t a n w i n d o w . A f t e r p a s s i n g t h r o u g h a b o u t 6 cm of air the ions hit t h e m i e r o e l e c t r o n i c d e v i c e s w i t h a r e d u c e d e n e r g y g i v e n in T a b l e 1. The L E T and t h e r a n g e o f t h e p a r t i c l e s in s i l i c o n e q u i v a l e n t to t h i s e n e r g y is also given in T a b l e 1. For d e v i c e s e x p o s e d w i t h i n c i d e n t a n g l e s not e q u a l to z e r o t h e e f f e c t i v e LET/cosc~ is g i v e n . For t h e high e n e r g y runs w i t h Ne and Au also e x t r a c t e d b e a m s in air w e r e u s e d . The e n e r g y l o s s o f t h e s e p a r t i c l e s in t h e air can be n e g l e c t e d . The L E T v a l u e and r a n g e given for t h e s e p a r t i c l e s w a s d e t e r m i n e d for t h e b e a m e n e r g y . T a b l e 1. L i s t of e x p o s u r e s with d i f f e r e n t ion b e a m s , t h e p a r t i c l e e n e r g y in t h e b e a m p i p e , e n e r g y , c a l c u l a t e d e n e r g y loss on d e v i c e s u r f a c e , t h e r a n g e o f t h e p a r t i c l e s in t h e d e v i c e and t h e p r e l i m i n a r y r e s u l t s for c r o s s s e c t i o n s of H a r r i s H M I - 6 5 1 6 2 - 2 2 k o g b i t SRAM ion
20Ne 20Ne 20Ne 40Ar 40Ar 40Ar 40Ar 40Ar 40At 197Au 251Cf 131Xe 197Au
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265 3667 5134 8532 9385 10238 11092 11945 11306 11949 40000 62000 89600
cross section
cm 2 ..... 1,1" 10 -5 2, 2. I0 - 5 3, 8" 10 - 3 7, 0" 10 -3 7, 6" 10 -3 9 , 6 " 10 - 3 8, 5" 10 -3 9, 5" 10 - 3 9, 8" 10 -3 2, 6" 10 -2 9, 1" 10 -2 1,9" 10 -1
Due to p r o b l e m s of a c c u r a t e b e a m flux m e a s u r e m e n t s it w a s only p o s s i b l e to get p r e l i m i n a r y r e s u l t s for t h e c r o s s s e c t i o n of t h e H M I - 6 5 1 6 2 - 2 d e v i c e for t h e d i f f e r e n t e x p o s u r e s . The b e a m m o n i t o r u s i n g PIN d i o d e s w h i c h will be u s e d in f u t u r e w a s not a v a i l a b l e during all t h e s e runs. P a r t i c l e f l u x e s had to be e s t i m a t e d b a s e d on n u c l e a r t r a c k d e t e c t o r s or on c o u n t s of not p e r f e c t l y c a l i b r a t e d PIN d i o d e s . T h e r e f o r e t h e m e a s u r e d c r o s s s e c t i o n s may have e r r o r s s i g n i f i c a n t l y l a r g e r than the s t a t i s t i c a l e r r o r r e s u l t i n g from the n u m b e r of u p s e t s o b s e r v e d . The s t a t i s t i c a l e r r o r s t y p i c a l l y r a n g e f r o m 5 to 10 p e r c e n t . In Fig. 2 c r o s s s e c t i o n s o f T a b l e 1 are p r e s e n t e d as a f u n c t i o n of LET. For t h e 11.6 M e V / N Xe and the 16 M e V / N Au e x p o s u r e s t h e m e a s u r e d c r o s s s e c t i o n s are s i g n i f i c a n t l y l a r g e r t h a n t h o s e for f i s s i o n p r o d u c t s of Cf. W e are c o n v i n c e d t h a t t h e s e r e s u l t s are not c a u s e d by u n c e r t a i n t i e s in b e a m flux c a l i b r a t i o n but o r i g i n a t e f r o m the f a c t t h a t a single ion can c a u s e m u l t i p l e b i t - f l i p s as it w a s o b s e r v e d b e f o r e ( M a r t i n et a l . , 1987) . In Fig. 3a and 3b t h e d i s t r i b u tions o f t h e n u m b e r of c o r r e l a t e d b i t - f l i p s c a u s e d by a s i n g l e p a r t i c l e are shown. For Xe a m e a n value o f 1.8 b i t - f l i p s p e r ion and for Au a m e a n value o f 2.2 b i t - f l i p s p e r ion w e r e o b s e r v e d . This m e a n s t h a t in t h e s e c a s e s the a r e a of p o t e n t i a l d a m a g e a r o u n d t h e t r a j e c t o r y is s i g n i f i c a n t l y l a r g e r t h a n t h e s i z e of a single s e n s i t i v e v o l u m e . B i t - f l i p s also can o c c u r e w h e n ions p a s s t h r o u g h i n s e n s i t i v e e l e m e n t s . This i n t e r e s t i n g p h e n o m e n o n is not d e s c r i b e d c o r r e c t l y by a c r o s s s e c t i o n of t h e form o = N/(F~,t) cm 2 with N = n u m b e r o f b i t - f l i p s o b s e r v e d . T h e r e f o r e t h e s e c r o s s s e c t i o n s w e r e n o t p r e s e n t e d in Fig. 2. N e v e r t h e l e s s a more d e t a i l e d s t u d y o f this phenomenon would be o f particular interest. For t h e 350 M e V / N Ne no s i g n i f i c a n t n u m b e r of S E U s was o b s e r v e d s i n c e on t h e one hand t h e e n e r g y loss by i o n i z a t i o n in t h e s e n s i t i v e l a y e r was too s m a l l and on t h e o t h e r h a n d t h e t e s t p e r i o d w a s not long e n o u g h to o b s e r v e t h e r a r e S E U s c a u s e d by the high a m o u n t of e n e r g y d e p o s i t e d by n u c l e a r i n t e r a c t i o n s of t h e Ne w i t h Si i n s i d e t h e d e v i c e . Our f i r s t p r e l i m i n a r y r e s u l t s are i m p o r t a n t for the p l a n n i n g o f f u t u r e t e s t s at t h e n e w SIS f a c i l i t y
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REFERENCES J . B . B l a k e , R . M a n d e l , On O r b i t O b s e r v a t i o n s Of S i n g l e E v e n t U p s e t .... I E E E T r a n s . Nucl. S c i e n c e , Vol. N S - 3 3 , No. 6, (1986) R . C . M a r t i n , N . M . G h o n i e m , T h e S i z e E f f e c t Of Ion C h a r g e T r a c k s .... I E E E T r a n s . Nucl. S c i e n c e , Vol. N S - 3 4 , (1987), P a g e 1305-1309 ~,V.E.Price, J . R . C o s s , S i n g l e E v e n t P h e n o m e n a : A S u m m a r y , N u c l . ]Instr. M e t h . , B 4 0 / 4 1 (1989), P a g e 1306-1309 P . A . R o b i n s o n jr. 1 r e . L e e , R . A g u e r o , S . B . G a b r i e i , A n o m a l i e s Due To S i n g l e E v e n t U p s e t s , A[AA 9 0 - 0 1 7 4 . 28 t n A e r o s o a c e S c i e n c e s M e e t i n g . J a n . 8-11, 1990, R e n o , N e v a d a