RESISTANCE SWITCHING CHARACTERISTICS IN POLYCRYSTALLINE SILICON FILM RESISTORS

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Vol. 132, No. 5

I n P E P I T A X I A L L A Y E R S 1193 Manuscript s u b m i t t e d April 30, 1984; revised manu-

script received Oct. 29, 1984.

AT&T Bell Laboratories assisted in meeting the publica-

tion costs of this article.

R E F E R E N C E S

1. G.H. Olson, C. J. Nuese, and M.

Ettenberg, Appl. Phys.

Let.,

34, 262 (1979).

2. W. D. J o h n s t o n , Jr., and K. E. Strege, I E E E 38th Device Research Conference, Abstract Vol. IV B-3, Ithaca, N e w York (1980).

3. G.H. Olson, in " G a I n A s P Alloy S e m i c o n d u c t o r s , " T. P. Pearsall, Editor, Chap. 1, J o h n Wiley and Sons, New York (1982).

4. S. N. G. Chu,

This Journal,

129, 2082 (1982).

5. S. N. G. Chu, C. M. Jodlauk, and A. A. Ballman,

ibid.,

129, 352 (1982).

6. S. N. G. Chu and T. T. Sheng,

ibid.,

To be published. 7. R. E. Nahory, M. A. Pollack, W. D. Johnston, Jr., and

R. L. Barns,

Appl. Phys. Lett.,

33, 659 (1978). 8. C. N. Cochran and L. M. Foster,

This Journal,

1{}9, 144

(1962).

9. D. Shaw,

J. Phys. Chem. Solids,

36, 111 (1975). 10 C. D. T h u r m o n d ,

ibid.,

26, 785 (1965).

11. M. G e r s h e n z o n and R. H. Mikulyak,

This Journal,

198, 548 (1961).

12. A. K o u k i t u and H. Seki,

J. Cryst. Growth,

49, 325 (1980). 13. R.F. Karlicek, Jr., and A. B. LaRoe, U n p u b l i s h e d work. 14. V. M. Donnelly and R. F. Karlicek,

J. Appl. Phys.,

53,

6399 (1982).

Resistance Switching Characteristics in Polycrystalline Silicon Film

Resistors

Chih-Yuan Lu*

AT&T Bell Laboratories, Reading, Pennsylvania 19603-0856; Institute of Electronics, National Chiao-Tung University,

Hsin-Chu, Taiwan, 300, China; Department of Electrical and Computer Engineering, North Carolina State University,

Raleigh, North Carolina 27695-7911

Nicky Chau-Chun Lu

IBM T J . Watson Research Center, Yorktown Heights, New York 10598

Chih-Ching Shih

Institute of Electronics, National Chiao-Tung University, Hsin~Chu, Taiwan 300, China

A B S T R A C T

B o t h reversible and irreversible resistance switchings have been investigated in boron- and arsenic-doped L P C V D polycrystalline silicon film resistors. The effects of film thickness and doping concentration on the transition voltage and current h a v e b e e n characterized for different length resistors having film thickness from 0.1 to 1.2 t~m and doping concentration ranging from 5 • 10 TM to 1 • 10 z~ cm -3. U n d e r a large voltage bias, the resistor can be switched to a conduc-

tive " o n " state or to a "short" state having resistance reduction by a factor of 103-106, or it can be b l o w n "open". The transition voltage and current and the resistance after switching depend strongly on film thickness, doping concentration, and applied power. A simple qualitative m o d e l is proposed to explain these resistance switching p h e n o m e n a .

Polycrystalline silicon (polysilicon) films have been widely used as solar cell and integrated-circuit elements, and such applications have stimulated extensive studies of the electrical properties of this material. B o t h reversible and irreversible resistance switching p h e n o m e n a have b e e n reported (1-3). The irreversible resistance switching has b e e n extensively applied to integrated- circuit applications, such as a m e m o r y e l e m e n t in fusible- link P R O M ' s (3-5) and a fuse or antifuse in r e d u n d a n c y circuits in high density RAM's (6). However, there are a limited n u m b e r of papers in the literature systematically studying resistance switching properties of polysilicon resistors. Greve studied the p r o g r a m m i n g m e c h a n i s m of heavily d o p e d polysilicon resistor fuses and showed that formation of a s e c o n d - b r e a k d o w n state is necessary to blow open the fuses (1). He also studied n~-p-n § polysilicon devices and showed that the dopant migration and the a l u m i n u m penetration in m o l t e n filaments through polysilicon devices are the m e c h a n i s m s for resistance switching (7, 8). On the other hand, Mahan reported a reversible switching p h e n o m e n o n in u n d o p e d polysilicon resistors having high v a l u e resistance (2).

This work reports n e w e x p e r i m e n t a l results on the effects of film thickness, doping concentration, and device dimensions on resistance switching behavior in polysilicon resistors. The resistances before and after switching, the switching IrV curves, and the transition voltage

*Electrochemical Society Active Member.

and current beyond which the switching occurs were characterized extensively. Different switching patterns have b e e n clearly identified from this systematic study, and a better physical understanding of the switching behavior in polysilicon resistors has b e e n obtained from a qualitative model.

Sample Preparation and Measurements

A 0.80 tLm thick oxide was grown at ll00~ on top of N-type (100) silicon wafers with resistivity of 4 - 7 ~l-cm. U n d o p e d polysilicon films with thickness ranging from 0.1 to 1.2 tLm were deposited in a low pressure CVD reac- tor at 620~ with deposition rate of 80 •/min. Either boron or arsenic dopants were t h e n i m p l a n t e d with various doses to yield doping concentrations from 5 • 1026 to 1 x 10 ~~ c m -3 for arsenic and from 5 • 10 TM to 2 • l0 is cm -3 for

boron. After polysilicon resistors were patterned by plasma etching, an 8000~ CVD o x i d e layer was deposited at 430~ to avoid dopant evaporation during s u b s e q u e n t thermal steps. F o r p-type samples, the contacts were either u n d o p e d or heavily doped with boron. For n-type samples, the contacts were all heavily doped with arsenic to avoid S c h o t t k y barrier formation. All samples were an- nealed at 900~ for 60 rain to activate and uniformly redis- tribute the dopants, as well as to r e m o v e the i m p l a n t a t i o n damage. A 1.0 ~ m thick a l u m i n u m layer was deposited and etched to f o r m the contact pattern. The contacts were sintered in N2 at 450~ for 20 rain.

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address. Redistribution subject to ECS terms of use (see 140.113.38.11

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1194 J. E l e c t r o c h e m . Soc.: S O L I D - S T A T E S C I E N C E A N D T E C H N O L O G Y M a y 1985 T h e t h i c k n e s s of p o l y s i l i c o n films was m e a s u r e d by an

optical m e t h o d ( N a n o s p e c M o d e l Axp-010-0180) a n d an a-step profiler. M e a s u r e d electrical p r o p e r t i e s o f p o l y s i l i c o n r e s i s t o r s i n c l u d e zero bias r e s i s t a n c e a n d I-V characteristics. T h e m e a s u r e m e n t s y s t e m s were: (i) a n H P 4140B p i c o a m p e r e m e t e r w i t h dc p r o g r a m m a b l e v o l t a g e source, c o u p l e d to an HP-85 m i c r o c o m p u t e r to m e a s u r e t h e zero bias r e s i s t a n c e , a n d (ii) a T e k t r o n i x 576 c u r v e t r a c e r to o b s e r v e I-V characteristics a n d to t r i g g e r polysil- i c o n - r e s i s t a n c e s w i t c h i n g . T h e s u r f a c e of resistors after s w i t c h i n g was s t u d i e d b y an optical m i c r o s c o p e a n d a s c a n n i n g e l e c t r o n m i c r o s c o p e (SEM).

Results

T h e g e n e r a l b e h a v i o r of t h e I-V characteristics of p o l y s i l i c o n resistors is i l l u s t r a t e d in Fig. 1. T h e I-V c u r v e of p o l y s i l i c o n resistors b e f o r e s w i t c h i n g follows t h e pre- d i c t e d h y p e r b o l i c sine f u n c t i o n ( c u r v e 1) (9, 10) to a cer- tain p o i n t A. It was f o u n d t h a t t h e h i g h v o l t a g e p a r t of c u r v e t was n o t stable for m o s t d e v i c e configurations. T h e r e s i s t i v i t y drastically d e c r e a s e s w i t h i n c r e a s i n g voltage, a n d w o u l d c o n t r a c t to a stable c u r v e 2 ( " o f f ' state) (2). W h e n v o l t a g e i n c r e a s e s a l o n g c u r v e 2, a n e g a t i v e resist- a n c e b e h a v i o r m a y appear. W h e n t h e v o l t a g e f u r t h e r increases, t h e I-V c u r v e s of d e v i c e s o f l i g h t d o p i n g c o n c e n - tration a n d short d i m e n s i o n s w e r e s w i t c h e d to a m o r e c o n d u c t i v e " o n " state (curve 3). W h e n t h e p o w e r of t h e c u r v e t r a c e r w a s l i m i t e d b e l o w a c e r t a i n value, t h e nega- t i v e r e s i s t a n c e c h a r a c t e r i s t i c is s t a b l e a n d t h e s w i t c h i n g b e t w e e n c u r v e 2 a n d 3 is r e v e r s i b l e . T h i s r e v e r s i b l e s w i t c h i n g in p o l y s i l i c o n film w a s r e p o r t e d b y M a h a n as " t h r e s h o l d s w i t c h i n g " (2). W h e n m o r e p o w e r was a d d e d into t h e resistor, a s u d d e n c h a n g e f r o m " o n " state ( c u r v e 3) to t h e " s h o r t " state (curve 4) o c c u r r e d for t h i c k film devices. H o w e v e r , for t h i n film devices, m o r e p o w e r can c a u s e t h e r e s i s t o r to " o p e n " ( c u r v e 5). B o t h s w i t c h i n g s f r o m c u r v e 3 to 4 a n d f r o m 3 to 5 are irreversible. F o r me- d i u m a n d h e a v i l y d o p e d p o l y s i l i c o n resistors, t h e switching always j u m p s d i r e c t l y f r o m " o f f ' state to e i t h e r " o p e n " or " s h o r t " state w i t h o u t g o i n g t h r o u g h t h e " o n " state. F o r e x a m p l e , in b o r o n - d o p e d s a m p l e s w i t h NA I> 5 x 10 '7 c m -3, no s w i t c h i n g to " o n " state has b e e n observed. H o w e v e r , for short a n d l i g h t l y d o p e d s a m p l e s (NA --< 1 • 1017 c m -~, a n d n o m i n a l l e n g t h less t h a n 15 ~m), re- v e r s i b l e s w i t c h i n g was o b s e r v e d . S i m i l a r o b s e r v a t i o n s w e r e m a d e on a r s e n i c - d o p e d polysilicon resistors, a n d t h e s a m e c o n c l u s i o n s w e r e o b t a i n e d . T h e s e v a r i o u s s w i t c h i n g p a t t e r n s are s u m m a r i z e d in Fig. 1. T h e r e v e r s i b l e s w i t c h i n g is m o r e l i k e l y to o c c u r for short a n d l i g h t l y d o p e d samples. No r e v e r s i b l e s w i t c h i n g has b e e n o b s e r v e d for o u r s a m p l e s w i t h d o p i n g level h i g h e r t h a n 1 x 10 '7 c m -3 a n d / o r l o n g e r t h a n 15 ~m. A l o n g t h e s t a b l e c u r v e 2, t h e v o l t a g e b e y o n d w h i c h t h e s w i t c h i n g o c c u r s is d e f i n e d as " t r a n s i t i o n v o l t a g e , " VT, a n d t h e c o r r e s p o n d i n g c u r r e n t as " t r a n s i t i o n c u r r e n t , " I~. T h e zero bias r e s i s t a n c e b e f o r e s w i t c h i n g is d e f i n e d as Rb a n d after s w i t c h i n g as R~. F i g u r e 2 s h o w s t h e t r a n s i t i o n v o l t a g e a n d r e s i s t a n c e vs. d o p i n g c o n c e n t r a t i o n for b o r o n - d o p e d r e s i s t o r s w i t h l e n g t h s of 10 a n d 5 ~ m b e f o r e a n d after switching. T h e resistance b e f o r e s w i t c h i n g s t r o n g l y d e p e n d s on t h e d o p i n g c o n c e n t r a t i o n , e s p e c i a l l y a r o u n d a critical d o p i n g c o n c e n - tration N* w h e r e m o s t of t h e g r a i n s c h a n g e f r o m total de- p l e t i o n i n t o partial depletion, t h u s c a u s i n g a drastic c h a n g e of r e s i s t a n c e (10). A n i n t e r e s t i n g p h e n o m e n o n is t h a t t h e t r a n s i t i o n v o l t a g e has s h o w n a m a x i m u m a r o u n d N*. A w a y f r o m N* on t h e h e a v i l y d o p e d side, t h e transition v o l t a g e g e n e r a l l y follows t h e d e c r e a s i n g p a t t e r n of R~. It w a s also f o u n d t h a t t h e t r a n s i t i o n v o l t a g e scales pro- p o r t i o n a l l y to t h e r e s i s t o r length. R e s i s t a n c e after s w i t c h i n g d e c r e a s e s b y a f a c t o r o f 10"L10t F o r t h e short a n d l i g h t l y d o p e d s a m p l e s , t h e r e s i s t o r m o s t l y s w i t c h e d first to " o n " , t h e n to " o p e n " r a t h e r t h a n " s h o r t " . As t h e m a x i m u m p o w e r of t h e c u r v e t r a c e r w a s raised f r o m 0.5 to 2.2W, t h e r e s i s t a n c e after s w i t c h i n g (already " s h o r t " ) c a n be f u r t h e r r e d u c e d b y a f a c t o r o f 10~-10 ~. Fi- I T i l l IZ) l F t 1

LONG 8 SHORT 8 SHORT 8

THICK THICK THIN

A) ON" ~' ~ ~' ~ ) 15) " S H O R T " ' LIG~TLu DOPED \ % I

vT

V O L T A G E (5) "OPEN"

Fig. 1. The general I-V switching behavior of polysilicon resistors

I

LONG Ti~N

151

nal resistance is a p p r o x i m a t e l y several o h m s a n d relatively i n d e p e n d e n t of d o p i n g c o n c e n t r a t i o n (Fig. 3). S h i n y a l u m i n u m penetration p a t h w a s f o u n d in these further "short" state resistors, w h i c h a c c o u n t s for the l o w resistance.

F i g u r e 4 s h o w s the relationship b e t w e e n film thickness a n d m e a s u r e d resistances before a n d after s w i t c h i n g for t w o d o p i n g concentrations of 1 • 1017 a n d 2 • I0 TM c m -3.

T h e resistance before s w i t c h i n g decreases drastically as the film thickness increases for resistors at d o p i n g concentration of 2 • 1018 c m -3, b u t not so m u c h for resistors at d o p i n g c o n c e n t r a t i o n of I • 10 '7 c m -3. T h e details of effect of d o p i n g effect o n resistivity vs. film thickness w a s investigated b y L u et al. (12). A l m o s t all the devices w i t h film thickness less t h a n 2 0 0 0 ~ w e r e s w i t c h e d to " o p e n " state, a n d R ~ is infinite.

T h e b e h a v i o r of V T vs. film thickness is s h o w n in Fig. 5. It is similar to the relationship of R b vs. film thickness in Fig. 4, e x c e p t that for the thinnest s a m p l e at d o p i n g level of 2 • I0 TM c m -3, the transition voltage decreases a n d the

p o s t s w i t c h i n g w a s a n " o p e n " state instead of a "short" state. T h e similar b e h a v i o r b e t w e e n V T a n d R~ s u g g e s t s that J o u l e heating plays a n i m p o r t a n t role in the switching m e c h a n i s m (I, 2).

F i g u r e 6 s h o w s the V T a n d IT of b o r o n - d o p e d resistors at d o p i n g level of 2 • i0 's c m -'~ for various film thicknesses. T h e r e is n o significant difference w h e t h e r the contacts h a v e b e e n heavily d o p e d or not (12). It is f o u n d that o v e r the o b s e r v e d r a n g e of film thickness, IT a n d V T o b e y a n

250 - - i . . ~ l l J IOI~ 0 " ~ 0 ~ 1 1 " ~ - LPCVD BORON _ 109 ~ E ~ I I WR = 50/J,m TR = 0.2/J.m - - BEFORE _ 2O0 IO s / / ! ~ TRANSITION /' ! ~\-'z-" .... AFTER I07 "' / t ( - ~ TRANSITION (~ C9 < 150 .' t \ \ - - - TRANSITION lOS uJ > j ', ~ VOLTAGE (,.) \ 105 z z 9 . . . '\ ~-

0 I00 9 LR=IOF. m "'~IB, '\ r

t ~' ' L U r- ~ LR=5~,m

/'~ f'-%~

,04 z I03 <c n / i ~ I \ = -;," ... o---J--I ~-- I0 2 5 0 0 ~ I | I 0 i 0 . . . 0 0 I I I 100 1016 i017 ,,!'~ 1018 1019 DOPING CONCENTRATION (cm -5)

Fig. 2. Transition voltage and resistance vs. (loping level before end offer switching (power ~< O.5W).

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Vol. 132, No. 5

P O L Y C R Y S T A L L I N E SILICON F I L M R E S I S T O R S

1195

2 5 O F ' ~ , , ~ i

i

1 m,o

/ r'l"-r.1 ~ l l LPCVD BORON

~ E ~ WR = 50ju.m TR'O.Zp-m toe

^ 2 o o - - B E F O R E

.."~ ~

TRANSmON lOS

_ _ / L ~ \ .... AFTER I0 7 / i \ \ TRANSITION 150

/"

i i "~ ---TRANSITION I06 "~ 0 / ~ B VOLTAGE 0 > 9 IO 5 z 9 LR=lO/~m ~' 0 f-I L R= 5/J.m \ ~- too _/Io \ 1o 4 _,,, z / i \ E ,~ - - / , \ io 3 i,- / / I I02

5o

o

t I b . . . m' . . . , ,oo 1016 i017 !* 1018 1019 DOPING CONCENTRATION (cm -3)

Fig. 3. Transition voltage and resistance vs. doping level before and after switching (power ~< 2 . 2 W ) .

empirical expression

Iv = Io[exp

(VJVT)]

where lo and Vo are empirical parameters.

D i s c u s s i o n

A simple qualitative model is proposed to u n d e r s t a n d the above observations. When the applied voltage is be- low the transition voltage, the I-V characteristics of polysilicon resistor can be described by the carrier trapping a n d dopant-segregation models (9-13). According to these models, the active d o p a n t concentration can be obtained by subtracting the inactive segregated d o p a n t concentration from the actual doping concentration (10, 11), and the grain-boundary trapping states can trap free carriers from the ionized active d o p a n t s a n d act as recombination centers (14, 15). This trapping process reduces the n u m b e r of free carriers and creates built-in potential barriers s u r r o u n d i n g the grain boundary, which i m p e d e carrier motion from one crystallite to another. The carrier transport across the grain b o u n d a r y a n d the built-in potential barriers by thermionic emission a n d t u n n e l i n g processes show a hyperbolic sine function I-V characteristic (13).

As the applied voltage further increases, the forward- biased space-charge barrier can eventually be flattened

108 cl 107 P _~ 106 oc I05 r ZPCVDIARsEINJC I 1012 F L R= IO/J'm WR = 50/r m II / A \ 9 N= hdOlTcm-:5 I0 i-- ~ A 9 -3

,e,OL

'+\

109 ~ A BEFORE TRANSITION 104 . . . AFTER TRANSITION

103 ///"

""',%

10 2 ," " 9 i- ... a I01 I I I I "'-A I 0.0 O. 2 0.4 0.6 0.8 1.0 1.2 FILM THICKNESS (/r

Fig. 4. Resistance vs. film thickness before and after switching

250 i i i i . o o LR= lO~m A 9 N = ix IOItcm "s 150 X A N=ZxlOIScrn -3 IOO X A 0 I I I I I 0.0 0.2 0.4 0.6 0.8 1.0 1.2 FILM THICKNESS (p.rn)

Fig, 5. Transition voltage vs. film thickness

and a great n u m b e r of carriers is then injected into the resistors. Once this happens, bulk resistance of silicon crystallite becomes dominant, and the I-V characteristic ex- hibits a transition from "grain-boundary limited" to "bulk-limited" condition. Thus the observation that transition voltage reaches a m a x i m u m value around the critical doping concentration can be understood by the fact that the highest built-in potential barrier exists at this doping concentration (10) and, therefore, a higher voltage is needed to flatten the forward-biased built-in potential barrier.

For lightly doped polysilicon films, the crystallites are totally depleted by the grain-boundary trapping states, a n d hence the films are nearly intrinsic. The resistivity of totally depleted polysilicon films is very high, a n d this semi-insulating property is m a i n l y due to carrier depletion rather t h a n mobility degradation (10). If a finite voltage which is large enough to flatten the built-in potential barrier is applied across the resistor, a large n u m b e r of electrons a n d holes can be injected at the cathode a n d the anode, respectively. Because there are more u n f i l l e d grain-boundary traps for capturing minority carriers t h a n for majority carriers, the lifetime of minority carriers is shorter.

If the resistor is long compared to the m e a n free path of minority carriers, the minority carriers are not able to transverse the resistor, a n d this condition results i n single injection. U n d e r a high current level, majority-carrier single injection is space-charge limited (16). However, as the bias is further increased, the field across the resistor eventually becomes high enough to allow the minority

i t I I r I l LPCVD BORON ] LR=IOp'm, WR=5Op'm I N = 2xlO 18 cm "3 I @AWlTH CONTACT A.J40

60 'o o~wiT.OUT CONTACT / " t

30 i- < 40 z

0 e..

z 30 20 o

./,./,

z

o

ao

E

-tO v- I0 P I I I 0.0 0.2 0.4 0,6 0.8 1.0 1,2 FILM THICKNESS (/zm)

Fig. 6. Transition voltage and transition current vs. film thickness

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1196 J. E l e c t r o c h e m . Soc.: S O L I D - S T A T E S C I E N C E A N D T E C H N O L O G Y M a y 1985 carriers to reach the other end of the resistor. This double

injection process causes the majority space-charge barrier to be lowered and minority carrier lifetime (mobility) to increase, p e r m i t t i n g m o r e carriers to transit the resistor; as a result, a lower voltage is required to provide the current for maintaining the condition. This positive feedback process results in negative resistance characteristics. The condition causing this negative resistance behavior is that the minority carrier transit time is equal to their lifetime. It is clear that in a shorter resistor it is easier to reach this condition. Eventually, the high level injection condition will be reached w h e n the lifetimes of minority and majority carriers are equal. A t this point, two-carrier recombination-limited current flow prevails and the negative resistance behavior terminates; the polysilicon resistor can then switch to the " o n " state. This double injection mode is m u c h more likely observed for small grain and/or lightly doped polysilicon films w h i c h have plenty of recombination centers for both majority and minority carriers (17).

Similar p h e n o m e n a have b e e n observed in m a n y amorphous semiconductors w h e r e the initiation of switching and the maintenance of the "on" state in threshold switching can be satisfactorily explained as a double injection electronic process (18, 19). U n d o p e d or lightly doped polysilicon films of small grain size have m a n y properties close to a m o r p h o u s films. J u s t like any electronic transport process, heat will be generated by current, and thermal effects will a c c o m p a n y this electronic injection process. For short polysilicon resistors, however, the high field induced carrier generation is more likely to occur before thermal effects take over the major role. Therefore, if the d o u b l e injection process and positive feedback m e c h a n i s m occur before J o u l e heating makes any microstructure change, a reversible threshold switching occurs. However, if m o r e p o w e r is fed into the "on" state resistor, the J o u l e heating will finally b e c o m e large enough to cause an irreversible switching from " o n " state to "short" or " o p e n " state.

For heavily d o p e d polysilicon films, although the grain-boundary trapping states are completely filled up with majority carriers, the concentration of free majority carriers is still substantially larger than the intrinsic carrier concentration and of the same order of m a g n i t u d e as the active doping concentration (10, 11). The lifetime of minority carrier is m u c h shorter than that of majority carrier. This majority carrier transport process is not space- charge limited. The double injection condition is hardly reached even u n d e r a relatively large bias. Usually, the thermal process will t h e n prevail to induce current filamentation (20). Thermal current filamentation results in irreversible switching to either "short" or " o p e n " state, depending on the configuration of resistor and program- ming conditions. F o r thick and short resistors, thermal filamentation can induce either dopant migration or alu- m i n u m penetration through the molten filament to form "short" state (1). For thin and long resistors, J o u l e heating can simply evaporate the polysilicon film to leave a void (21), or the applied field can be strong enough to sweep the molten silicon ions to form an " o p e n " gap (1).

It should be noted that the coexistent electronic and thermal processes always c o m p e t e and influence each other. Therefore, the device configuration, composition of the resistor, and the p r o g r a m m i n g conditions all have their roles and b e c o m e a control parameter in some par- ticular stage of this c o m p l e x switching p h e n o m e n o n .

Conclusion

Several distinct patterns of polysilicon resistance switching have been observed for both arsenic- and

boron-doped materials over a wide range of doping concentration and film thickness. The transition voltage reaches a m a x i m u m value around the critical doping concentration, which separates the totally d e p l e t e d and par- tially depleted cases. B e y o n d this point, toward higher doping levels, the transition voltage generally follows the variation of Rb. As applied p o w e r increases, resistance after switching to "short" state can be further decreased and becomes less d e p e n d e n t on film thickness and doping level and, finally, a l u m i n u m penetration occurs, causing a resistance of only a few ohms.

Lightly doped resistors are more likely to show reversible threshold switching, probably due to their abundant recombination centers. Short and thick resistors are more likely to switch to "short" state, and the a l u m i n u m penetration path can be easily observed. L o n g and thin resistors are more likely to switch to " o p e n " state, and a physical gap is observed. These distinct patterns have been understood by a qualitative model.

Acknowledgments

The authors wish to thank Dr. Ming-Kwang Lee of ERSO, Industrial Technology Research Institute, ROC, for sample preparation, and Professor Si-Chen Lee of Na- tional Taiwan University for many valuable discussions. C. Y. Lu wishes to thank Dr. A. R e i s m a n for his encour- agement and support during his stay in N C S U and MCNC. We also would like to t h a n k Dr. L. M. Terman for helpful c o m m e n t s and C. Winston for typing this paper.

Manuscript submitted J u n e 11, 1984; revised manuscript received Dec. 7, 1984.

IBM Corporation assisted in meeting the publication costs of this article.

R E F E R E N C E S

1. D. W. Greve, IEEE Trans. Electron Devices, ed-29, 719 (1982).

2. J. E. Mahan, Appl. Phys. Lett., 41, 479 (1982).

3. M. Tanimoto, J. Murota, Y. Ohmori, and N. Ieda, IEEE Trans. ELectron Devices, ed-27,517 (1980).

4. R. K. Wallace, ISSCC Dig. Tech. Papers, 148 (1980). 5. L. R. Metzger, IEEE J. Solid-State Circuits, sc-18, 562

(1983).

6. T. Mano, K. Takeya, T. Watanabe, N. Ieda, K. Kiuchi, E. Arai, T. Ogawa, and K. Hirata, ibid., sc-15, 865 (1980). 7. D. W. G r e v e and L. V. Trans, IEEE Trans. Electron De-

vices, ed-29, 1313 (1982).

8. M. E. L u n n o n and D. W. Greve, J. Appl. Phys., 54, 3270 (1983).

9. G. J. Korsh and R. S. Muller, Solid-State Electron., ~1, 1045 (1978).

10. N. C. C. Lu, L. Gerzberg, C. Y. Lu, and J. D. Meindl, IEEE Trans. Electron Devices, ed-28, 818 (1981). 11. M. M. Mandurah, K. C. Saraswat, C. R. Helms, and T. I.

Kamins, J. Appl. Phys., 51, 5755 (1980).

12. N. C. C. Lu, C. Y. Lu, M+ K. Lee, C. C. Shih, C. S. Wang, W. Reuter, and T. T. Sheng, This Journal, 131, 897 (1984).

N. C. C. Lu, L. Gerzberg, C. Y. Lu, and J. D. Meindl, IEEE Trans. Electron Devices, ed-30, 137 (1983). H. C. Card and E. S. Yang, ibid., ed-24, 397 (1977). W. Hwang, E. Poon, and H. C. Card, Solid-State Elec-

tron., 26, 599 (1983).

M. A. L a m p e r t and P. Mark, " C u r r e n t Injection in Sol- ids," A c a d e m i c Press, New York (1970).

M. Braustein, A. I. Braustein, and R. Zuleeg, Appl. Phys. Lett., 10, 313 (1967).

D. Adler, M. S. Shur, M. Silver, and S. R. Ovshinsky, J. Appt. Phys., 51, 3289 (1980).

D. Adler, H. K. Henisch, and N. Mott, Rev. Mod. Phys., 50, 209 (1978).

D. H. Pontius, W. B. Smith, and P. P. Budenstein, J. Appl. Phys., 44, 331 (1973).

R. J. Smith, IEEE IEDM Tech. Dig., 608 (1982). 13. 14. 15. 16. 17. 18. 19. 20. 21.