chapter3 diode
TRANSCRIPT
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The Devices:
Diode
[Adapted from Rabaey’s Digital Integrated Circuits , ©2002, J. Rabaey et al.]
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Goal of this chapter• Present int itive nderstanding of deviceoperation
• Introd ction of !asic device e" ations
• Introd ction of #odels for #an al anal$sis
• Introd ction of #odels for SPI%E si# lation
• &nal$sis of secondar$ deep's !'#icron e(ects
• ) t re trends
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* tlineMotivation and GoalsSemi ond! tor "asi s#iode Str! t!re$peration% Stati model
& #epletion apa itan e & 'arrier density profiles
#iff!sion apa itan e% #ynami response
& S(it )in* speed ne+t session
Spi e model
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Se#icond ctor +asics Ile trons in intrinsi -p!re Sili on
% ovalently bonded to atoms% / !**led1 bet(een nei*)bors% t)ermally a tivated density ∝ e T
% move aro!nd t)e latti e, if free% leave a positively )ar*ed 3)ole’ be)ind
http:,,---.#asstech.org,cleanenerg$,solar/info,i#ages,cr$stal.gif
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Se#icond ctor +asics II4(o types of intrinsi arriers
% le trons -n i and )oles -p i% 5n an intrinsi -no dopin* material, n i6p i% At 7008, n i6p i is lo( -90 90 m:7
% ;se dopin* to improve ond! tivity
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Se#icond ctor +asics III+trinsi arriers
% Also t(o types of dopants -donors or a eptors & #onors brin* ele tron -n:type and be ome −ive ions & A eptors brin* )oles -p:type and be ome +ive ions
% S!bstantially )i*)er densities - ≥90 9< m:7% Ma ority and minority arriers
& if n==p -n:type ele trons ma ority and )oles minority & Random re ombination and t)ermal *eneration
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The Diode
p
n
B A SiO 2Al
Cross section of pn- junction in an IC process
P-type regiondoped -ithacceptori#p rities0!oron
N-type regiondoped -ithdonor i#p rities0phosphor s2arsenic
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The Diode
A
B
n
p
A
B
Al
One-dimensionalrepresentation diode symbol
The pn region isass #edto !e thin 0step orabrupt
3 nction
Di(erent concentrations ofelectrons 0and holes of the p and n 't$pe regions ca se aconcentration gradient at the!o ndar$
Si#pli ed str ct re
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• %oncentration Gradient ca ses electrons to difuse fro# n to p 2 and holes to di( se fro# p to n
• This prod ces i##o!ile ions in the vicinit$ of the!o ndar$
• egion at the 3 nction -ith the charged ions is calledthe depletion region or space-charge region
• %harges create electric eld that attracts the #inorit$carriers2 ca sing the# to dri t
• Dri t co nteracts difusion ca sing e" ili!ri # 0 Idri t =-Idifusion )
Depletion egion
hole diffusionelectron diffusion
p n
hole driftelectron drift
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Depletion egionhole diffusion
electron diffusion
p n
hole driftelectron drift
ChargeDensity
Distancex+
-
lectricalx!ield
x
"otent ial#
ξ
ρ
$ 2-$ %
ψ 0
&a' Current flo()
&b' Charge density)
&c' lectric field)
&d' lectrostatic potential)
• 6ero !ias conditions
• p #ore heavil$doped than n (N A >
N )
• Electric eld givesrise to potentialdi(erence in the
3 nction2 7no-n asthe built-in potential
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+ ilt'in Potential
8here φ T is the ther!al "oltage
Φ Φ* 2
= T
A D
i
N N
nln
'**&2, K at mV qkT T ==Φn i is the intrinsic carrier concentration for
p re Si 0 1.5 9 1 1 c# '; at ; < 2 so for
( ) mV mV ,+-
%*./)%
%*%*ln2, 2%*
%,%/
* ==Φ
0%%*0%%* +%,
+%/ ==
cm N
cm N
B A
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)or-ard +iashole diffusion
electron diffusion
p n
hole driftelectron drift
= '
• &pplied potential lo-ers the potential barrier 2 Idi( sion > I drift
• ?o!ile carriers drift thro gh the dep. region into ne tral regions
• !eco#e e#cess !inority carriers and di( se to-ards ter#inals
• ead a!o t drift and di( sion c rrents at:
• http:,,ece'---.colorado.ed ,@!art,!oo7,!oo7,chapterA,chA/1 .ht#
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)or-ard +ias
pn0
np0
-W1 W20
p n ( W 2 )
n-regionp-region
Lp
diffusion
Typically avoided in Digital ICs
xWn
? e
t a l c o n t a c
t t o n ' r
e g
i o n
-Wp
p (x)n
n (x)p
#inorit$ carrier concentration
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everse +iashole diffusion
electron diffusion
p n
hole driftelectron drift
' =
• &pplied potential increases the potential barrier
• Di( sion c rrent is red ced
• Diode -or7s in the reverse !ias -ith a ver$ s#all driftc rrent
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everse +ias
x
n p*
-$ % $ 2*
n-region p-region
pn*
diffusion
The Dominant Operation Mode
-Wp
Wn
? e
t a l c o n t a c
t t o n ' r
e g
i o n
n p*
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?odels for ?an al&nal$sis
V D
I D 6 I S -eV D>φT & 9.
?
–
V D
?
–
?
– V Don
I D
-a. 5deal diode model -b. @irst:order diode model
• &cc rate
• Strongl$ non'linear
• Prevents fast D% !iascalc lations
• %ond cting diodereplaced !$ voltageso rce V Don B .CV
• Good for rst order
appro i#ation
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T$pical Diode Para#eters
V D I D 6 I S-e V D>φT & 9
?
–
• DnBA5 c# A,sec
• DpB1 c# A,sec
• 8 nB5 µ#
• 8 pB .C µ#
• 8 AB .15 µ#
• 8 1B . ; µ#
Geo#etr$2 doping and #aterialconstants l #ped in Is
2%1%*
'&%
*
2
*
m A I valuetypical
qA I
S
W W
n D
W W
p D DS p
pn
n
n p
µ −
−−
=
+=
Di( sion coe cient#inorit$ carrier concentration
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Diode % rrent
Ideal diodee" ation:
V V Don 1)*≈
V V Don 1)*≈
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Depletion %apacitance
#!e to depletion )ar*es% # )an*es spa e )ar*e% @orms a apa itor C j
& ')ar*e mod!lated by volta*e
5deality fa tor -m depends on
!n tion *radient
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E" ivalent %apacitances I
BineariCe diode apa itan es% C j is a non:linear f!n tion of V D
& D)en bias )an*es t)en C j also )an*es & Eard to !se in man!al analyses
% 5nstead !se eF!ivalent apa itan e & Gives t)e same total )ar*e for a *iven V D transition
% F!ivalent depletion apa itan e & M!st be (or ed o!t for a *iven 9→ 2 transition
[ ]'%'&&
'&'&
'&'&
%2
%%*
%2**
*%2
%2
mV V V V
K
C K V V
V QV QV QC
mmm
eq
eq
D
eq
−−−−−−=
=−−=∆∆=−− φ φ φ
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E" ivalent %apacitances II
% F!ivalent diff!sion apa itan e & M!st be (or ed o!t for !rrents at *iven 9→ 2 transition
' eF depends on pro ess onstants and H 9, 2I% +ample
& for AD60.< µm 2 C j0 62 f@>µm 2, φ0 60. K and m60.<t)en e! ≈0. 22 and ' e! ≈9.2K f@>µm 2 if s(it )ed bet(een 0 and :2.< So !nit apa itan e C j ≈ 0.L f@>µm 2 or C j ≈ 0.K< f@ for t)e total diode area
%2
%2
%2
%2 '&'&'&'&
V V
V C V C
V V
V I V I
V
QC d d T
D DT
D
eq
−
−=−
−=∆
∆= φ τ
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Secondar$ E(ects:+rea7do-n
&2
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Diode SPI%E ?odel
ID
3 S
CD
+
-
# D
ReF!ired for ir !it sim!lations% M!st apt!re important )ara teristi s b!t also remain effi ient% +tra parameter in t)e model n -emission oeffi ient, 9 ≤ n< 2
& @i+es non:ideal be)avior d!e to bro en ass!mptions
Additional series resistan e a o!nts for body? onta tOonlinear apa itan e in l!des bot) C D and C j
I D = I S (eV D / nφ T −1)
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SPI%E Para#eters$ften s!pplied by t)e fab to t)e desi*ner % 5f not m!st be meas!red and fit t)e parameters
Ass!mes defa!lt val!es, if not e+pli itly definedPay attention to t)e !nits and spellin*