TCAD - BJT

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STRUCTURE OF BIPOLAR JUNCTION TRANSISTOR

The dimensions and doping of the proposed silicon BJT is shown in

Fig.1. This BJT is a vertical structure NPN and can be formed by successive

diffusion or successive implantation. The entire device is supported on a P -

substrate. n !thena process" successive implantation is done to achieve this

structure. The base width #Bis ta$en as %.&'m and base doping is (.)*1%1+,cm.

ow doping and lesser base width reduce the recombination process associated

with the base thereby increasing the BJT current gain /. The emitter width #0is

%.&)'m and emitter is highly doped at 1%&%,cm.The collector is a stac$ed layer

of n-type silicon of doping 1%1+,cmand a N-buried layer. The heavily doped

N

-buried layer is used to reduce the intrinsic collector resistance. 2ence wehave #B3#03#4 and N43PB3N0. The collector contact is ta$en from an N

implant to reduce the contact resistance.

N-type impurity used !resenic 5!s6

P-type impurity used Boron 5B6

Fig.1 Proposed structure of BJT

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Fig.& deal BJT structure formed using !T!7

Fig. Non-ideal BJT structure formed using !T20N!

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DOPING PROFILES

Fig.8 9oping profile in non-ideal BJT fabricated using !T20N! 5log scale6

Fig.) 9oping profile in ideal BJT fabricated using !T!7 5log scale6

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IC, IB vs VBE

Fig.+ 4"Bvs :B0in non-ideal BJT fabricated using !T20N!

Fig.( 4"Bvs :B0in ideal BJT fabricated using !T!7

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ICvs VCEat constant IB

Fig.; 4vs :40in non-ideal BJT fabricated using !T20N!

Fig.< 4vs :40in ideal BJT fabricated using !T!7

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RESULTS AND COMPARISON BETWEEN TWO

STRUCTURES

i6 The doping profile in case of the non-ideal structure is not well

defined. The doping profiles are =aussian shape whereas in the

ideal structure we have perfect step profiles.

ii6 The doping profiles are obtained by implantation. To flatten thedoping profile we can use annealing. But this techni>ue is not

suitable for smaller base and emitter width.

iii6 The current gain of the ideal structure is almost double the current

gain of the non-ideal structure. This is because the doping and base

width are not uniform.

iv6 The output impedance of the ideal structure is higher than the non-

ideal one.

v6 The non-ideal structure also needs higher voltage to turn the device

on indicated by a cut-in voltage difference of %.%8 :.

CONCLUSION

To obtain the ideal structure by process we can go for techni>ues li$e poly base

method. n this" we mas$ the silicon with undoped polysilicon and implant.

Then we anneal so that the profile enters into silicon. By this we can get thin

flat profiles called as bo*-li$e profiles.

CODE FOR NON-IDEAL BJT STRUCTURE

Non-i!a"St#$ct$#!I!a" St#$ct$#! Pa#a%!t!# S!#ia" No&

; 1( 4urrent =ain

/

1

1; ?@ 1&1 ?@ Autput mpedance

A

&

%.(+ : %.(& : 4ut-in :oltage:C

1;.; =2D - 4ut-off Fre>uency

fT

8

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go athena

line * locE%.% spacingE%.%()

line * locE%.< spacingE%.%()

line * locE1.& spacingE%.%)

line * locE1.( sapcingE%.%)line * locE&.< spacingE%.%()

line y locE%.% spacingE%.%()

line y locE%.& spacingE%.%)

line y locE%.) spacingE%.%)

line y locE1.) spacingE%.%()

init c.boronE1e1+

implant arsenic doseE(.)e1) energyE&)%

deposit silicon c.arsenicE1.1e1+ thic$nessE%.

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models conmob fldmob consrh auger print

contact nameEemitter n.poly surf.rec

solve init

method newton autonr trap

solve vcollectorE%.%&)

solve vcollectorE%.1solve vcollectorE%.&) vstepE%.&) vfinalE& nameEcollector

solve vbaseE%.%&)

solve vbaseE%.1

solve vbaseE%.&

log outfEbGtathena%.log

solve vbaseE%. vstepE%.%) vfinalE%.< nameEbase

tonyplot bGtathena%.log

log off

solve init

solve vbaseE%.%&)

solve vbaseE%.%)solve vbaseE%.1 vstepE%.1 vfinalE%.( nameEbase

contact nameEbase current

solve ibaseE1.e-+

save outfEbGtathena1.str master

solve ibaseE&.e-+

save outfEbGtathena&.str master

solve ibaseE.e-+

save outfEbGtathena.str master

solve ibaseE8.e-+

save outfEbGtathena8.str master

solve ibaseE).e-+

save outfEbGtathena).str master

load infEbGtathena1.str master

log outfEbGtathena1.log

solve vcollectorE%.% vstepE%.&) vfinalE).% nameEcollector

load infEbGtathena&.str master

log outfEbGtathena&.log


load infEbGtathena.str master

log outfEbGtathena.log

solve vcollectorE%.% vstepE%.&) vfinalE).% nameEcollectorload infEbGtathena8.str master

log outfEbGtathena8.log


load infEbGtathena).str master

log outfEbGtathena).log


tonyplot -overlay bGtathena1.log bGtathena&.log bGtathena.log bGtathena8.log

bGtathena).log

>uit

CODE FOR IDEAL BJT STRUCTURE

go atlas

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mesh

*.m lE% spacingE%.1

*.m lE%.< spacingE%.1

*.m lE1.& spacingE%.%)

*.m lE1.( spacingE%.%)

*.m lE&.< spacingE%.1

y.m lE%.% spacingE%.1

y.m lE%.& spacingE%.%)

y.m lE%.< spacingE%.%)

y.m lE&.8 spacingE%.1

region numE1 silicon

electrode nameEemitter *.minE1.&) *.ma*E1.+) y.ma*E%

electrode nameEbase *.minE1.;) *.ma*E&.%) y.ma*E%

electrode nameEcollector *.minE&.+ y.ma*E%

doping uniform p.type concE1e1+ y.minE1.8 regE1

doping uniform n.type concE1e&% y.minE%.< y.ma*E1.8 regE1

doping uniform n.type concE1e1+ y.ma*E%.< regE1

doping uniform p.type concE%.()e1( *.minE%.< *.ma*E& y.ma*E%.8 regE1

doping uniform n.type concE1e&% *.minE1.& *.ma*E1.( y.ma*E%.& regE1

doping uniform n.type concE1e&% *.minE&.) y.ma*E%.& regE1

models conmob fldmob consrh auger print

contact nameEemitter n.poly surf.rec

solve init

save outfEbGte*%8%.str

tonyplot bGte*%8%.str -set bGte*%8%.set

method newton autonr trap

solve vcollectorE%.%&)

solve vcollectorE%.1

solve vcollectorE%.&) vstepE%.&) vfinalE& nameEcollector

solve vbaseE%.%&)

solve vbaseE%.1solve vbaseE%.&

log outfEbGtatlas%.log

solve vbaseE%. vstepE%.%) vfinalE%.< nameEbase

tonyplot bGtatlas%.log

log off

solve init

solve vbaseE%.%&)

solve vbaseE%.%)

solve vbaseE%.1 vstepE%.1 vfinalE%.( nameEbase

contact nameEbase current

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solve ibaseE1.e-+

save outfEbGtatlas1.str master

solve ibaseE&.e-+

save outfEbGtatlas&.str master

solve ibaseE.e-+

save outfEbGtatlas.str mastersolve ibaseE8.e-+

save outfEbGtatlas8.str master

solve ibaseE).e-+

save outfEbGtatlas).str master

load infEbGtatlas1.str master

log outfEbGtatlas1.log


load infEbGtatlas&.str master

log outfEbGtatlas&.log

solve vcollectorE%.% vstepE%.&) vfinalE).% nameEcollectorload infEbGtatlas.str master

log outfEbGtatlas.log


load infEbGtatlas8.str master

log outfEbGtatlas8.log


load infEbGtatlas).str master

log outfEbGtatlas).log


tonyplot -overlay bGtatlas1.log bGtatlas&.log bGtatlas.log bGtatlas8.log bGtatlas).log

>uit

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TCAD - BJT