TELKOM
NIKA Indonesia
n
Journal of
Electrical En
gineering
Vol. 14, No. 2, May 2015, pp. 266 ~ 26
9
DOI: 10.115
9
1
/telkomni
ka.
v
14i2.774
7
266
Re
cei
v
ed Fe
brua
ry 2, 201
5; Revi
se
d
April 3, 2015;
Acce
pted April 20, 2015
Electrical Properties of Indium Doped Alumina (Al
2
O
3
)
Thin Films
Hada
ate Ulla
h
1
, Shahin Mahmud*
2
Dept. of Electrical and Electronic Engineering
(EEE), Southern universit
y
Bangladesh, B
angladesh
739/A, Meh
edi
bag R
o
a
d
, Chit
tagon
g.
Phon
e:
+
88028
69
343
(Ext.-20
2)
*Corres
p
o
ndi
n
g
author, e-ma
i
l
: sendb
ab
lu_
a
pee
@
y
ah
oo.co
m
1
, shahin@s
o
uthern.e
du.b
d
2
A
b
st
r
a
ct
T
o
know
the e
l
ectrical
prop
erties of a
n
y
mat
e
rials
is very
i
m
p
o
rtant for
pr
actical
ap
plic
ati
on of th
at
mater
i
al. In thi
s
paper I hav
e
tried to find o
u
t the pr
op
er electric
al pro
p
e
rties of Indi
u
m
d
ope
d Alu
m
in
a
(Al
2
O
3
) for practical ap
plic
ati
on of this Alu
m
i
na. F
o
r
this
purpos
e al
l thin fil
m
s ar
e
dep
osite
d
on
glass
substrate
by
electro
n
b
e
a
m
eva
porati
on t
e
chn
i
qu
e
at a
pressur
e
of
abo
ut 1.5 x
1
0
-6 torr
an
d
at
temp
eratur
e of
307K. T
h
e th
ic
kness
of Indi
u
m
do
ped
Al
2
O
3
fil
m
s (2
5%w
,
3
0
%w
an
d 4
0
%
w
of In
2
O
3
) range
from
68
n
m
t
o
1
83
n
m
. F
o
r 2
5
% In
2
O
3
do
ped
a
l
u
m
i
na th
e c
ond
u
c
tivity at ro
o
m
te
mper
atur
e i
s
24.10
mho/c
m
, for 30% In
2
O
3
dop
ed
alu
m
ina
this val
ue is
8
2
.99
m
h
o
/cm
a
nd for 4
0
% In
2
O
3
doped
al
u
m
in
a
th
i
s
i
s
12
9
.
10m
ho
/cm
.
The re
si
sti
v
i
t
y and
sh
ee
t
resist
ance
decr
eas
e w
i
th the i
n
crease
of do
pin
g
conce
n
tratio
n that means th
e cond
uctivity
inc
r
eases w
i
th do
pin
g
conc
entra
tion.
Ke
y
w
ords
: thin film
, indium
, alum
ina,
conductivity, concent
ration.
Copy
right
©
2015 In
stitu
t
e o
f
Ad
van
ced
En
g
i
n
eerin
g and
Scien
ce. All
rig
h
t
s reser
ve
d
.
1. Introduc
tion
Aluminum oxi
de (Al
2
O
3
) is
one of the most pop
ular el
ectri
c
al in
sula
ting material
s since it
has hi
gh ele
c
trical b
r
ea
kd
o
w
n field, larg
er ban
dga
p, and hig
h
diel
ectri
c
con
s
ta
nt. In particul
a
r,
Al
2
O
3
films h
a
ving thi
ckn
e
s
ses in the
ra
nge
of 50–
30
0 nm
are
inte
restin
g fo
r p
r
epari
ng th
e g
a
te
insul
a
tors in t
h
in film field
effect
tran
si
stors (FET
s). F
abri
c
ation
of
Al
2
O
3
thin
films can be d
one
by dc o
r
RF
magnet
ron
sputtering
of e
i
ther a
n
Al target in Al : O
2
mixtures (re
a
ctive sputtering)
[1-4], or by
sputtering
of a
n
Al
2
O
3
target
in pure Al, or Al : O
2
mixtu
r
es
[4-12]. Optimiz
a
tion of t
h
e
diele
c
tric
pro
pertie
s
, in p
a
rticular the ele
c
tri
c
al
resi
stivity and ele
c
tri
c
al b
r
ea
kd
own fields
of Al
2
O
3
films fab
r
icated by m
agn
etron
sp
utterin
g
wa
s
one
of
t
he mo
st im
po
rtant poi
nt of i
n
vestigatio
ns
in
the last year. Howeve
r, Diele
c
tri
c
co
nstant
s (
ε
) a
nd brea
kdo
w
n fields
were often used
to
descri
be the
electri
c
al p
r
o
pertie
s
of thin sputtere
d Al
2
O
3
films [6, 8–10, 12]. Current voltage (I–V)
curve
s
were
only repo
rted
in exception
a
l ca
ses [3
-5
], [7, 11]. Neverthele
ss, re
sea
r
che
r
s ha
ve
the highe
st l
e
vel of intere
st to those curves
as
th
e
y
contain inf
o
rmatio
n abo
ut the elect
r
i
c
al
con
d
u
c
tion m
e
ch
ani
sms le
ading
to u
n
wanted l
e
a
k
ag
e current
s, e.
g., acro
ss the
gate i
n
sulato
r in
a FET
struct
ure,
and
may
co
ntain i
n
formation
on th
e me
ch
anism
of the
ele
c
trical
bre
a
kdo
w
n
and the stati
s
tical a
nalysi
s
of the brea
kdo
w
n fiel
d
s
[9]. In
the prese
n
t pape
r, we have trie
d to
explain th
e t
he va
riation
s
of resi
stivity, co
ndu
ctivity and
sh
eet
re
sista
n
ce
with
re
sp
ect to
the
variation
s
of dopin
g
co
nce
n
tration in det
ail. Our
prim
e
con
c
ern is to
demon
strate
the influen
ce
of
the sputter p
a
ram
e
ters an
d to acqui
re i
n
sig
h
t in
the origin of the l
eakage
curre
n
ts as
well a
s
their
dep
end
ency
on
the
diele
c
tri
c
break do
wn
fie
l
ds. Atomi
c
f
o
rce mi
cro
s
copy data
of
the
surface m
o
rphology will be
reported along with the el
ectri
c
al measurem
ents.
In
2
O
3
is a se
micon
d
u
c
ting
material whi
c
h has a direct
band gap of about 3.6 eV [13] and
an indirect ba
nd gap of ap
proximately 2
.
6 eV [14].
Generally, it is
a yellow powder but it can
be
prep
ared a
s
a thin film which
ha
s the
pro
perty
of
transpa
ren
c
y
in the visi
bl
e sp
ect
r
um.
In
gene
ral, the
films
are
n
-
type
semi
co
ndu
ctors
d
u
e
to a
con
s
eque
nce of
deviation
s from
stoie
c
hiom
etric
com
positio
n, exce
ss in
dium
ato
m
s
or
oxygen v
a
ca
nci
e
s a
c
t as do
no
rs.
The
material
prop
erties which are
often de
scribe
d
in
th
e literatu
r
e
a
r
e
co
nsid
era
b
ly different
from
each othe
r. One imp
o
rta
n
t rea
s
on
b
ehind thi
s
is
that there
are lot
s
of d
i
fferences i
n
the
con
d
ition
s
of prep
aration a
nd co
nsequ
e
n
tly the oxi
dation state of the sa
mple
s is also different
.
It
has b
e
come
a difficult task to unde
rsta
nd the co
ndu
ction me
cha
n
i
sm in indiu
m
oxide thin films
becau
se of its co
mplicated
crys
tal
stru
cture (80 atom
s in an In
2
O
3
unit cell [15]).
Evaluation Warning : The document was created with Spire.PDF for Python.
TELKOM
NIKA
ISSN:
2302-4
046
Electri
c
al Pro
pertie
s
of Indium
Doped Al
um
ina (Al
2
O
3
) Thin Film
s (Had
aate Ulla
h)
267
“Thin Film
s”
can be d
e
fin
ed as a thin layer of solid
material which is formed o
n
a solid
sub
s
trate h
a
ving a thickne
ss of that ma
gnitude
wh
ich is com
p
a
r
a
b
le with mea
n
free path of
the
con
d
u
c
tion el
ectro
n
s of sol
i
d materi
al. Its value
ca
n vary from m
a
terial to m
a
teri
al. In most of
the
ca
se
s, a film
having
a thi
c
kne
s
s b
e
lo
w
a few mi
cro
m
eters
can
be
rega
rd
ed
as thin. The
thin
film
techn
o
logy is an importa
n
t
bran
ch of physi
cs
wh
e
r
e the cha
r
a
c
teristics of di
fferent metal
s
,
semi
con
d
u
c
tors an
d in
su
lators a
r
e i
n
vestigated
in the form of
thin film [16]. Mos
t
of
the
electroni
cs e
quipme
n
ts i
n
the mo
dern
worl
d a
r
e t
h
e
co
ntributio
ns of thin film t
e
ch
nolo
g
y. The
increa
sing d
e
m
and
s of microele
c
troni
cs
in sci
ence
an
d techn
o
logy have gre
a
tly stimulated aft
e
r
the invention
of thin film
and du
e to the ex
pan
sio
n
has be
en m
ade on diffe
rent kind
s of thin
films. System
atic
study
of
semi
-cond
uct
i
ng films ha
s
been
co
nt
inu
ed for mo
re t
han fifty years.
Primarily, se
mi cond
ucto
r films like Si, Ge etc.
we
re
studied. The
Si and Ge techn
o
logy is n
o
w
well e
s
tabli
s
h
ed [17]. No
w,
attention ha
s be
en
give
n
to the study
of comp
oun
d
semi
con
d
u
c
tor
mainly on th
e oxide
sem
i
con
d
u
c
tors (like Alumi
n
a
)
. The mo
st
comm
only u
s
ed
metho
d
to
prep
are the t
h
in films i
s
t
he the
r
mal
e
v
apor
atio
n te
chni
que
wh
ere the ato
m
s
are
co
nde
nsed
from vapo
r p
hase onto a
sub
s
trate. So
lid material
starts to vapo
rize
wh
en it is heate
d
to a
sufficie
n
tly high tempe
r
atu
r
e. One o
r
m
o
re p
h
a
s
e transfo
rmatio
n
s
are re
quire
d to achi
eve the
depo
sition of
films and t
he study of
the t
hermo
dynamics a
n
d
kineti
cs
of these p
h
a
s
e
transfo
rmatio
n exposes th
e formation of
thin films [18].
2. Deposi
t
ion Mechanis
m
Vacuu
m
eva
poratio
n is o
ne kin
d
of d
epo
sition techniqu
e whi
c
h
is used to d
epo
sit a
variety of m
a
terial
s by
mean
s of h
e
a
ting a
sou
r
ce m
a
terial
unde
r va
cuu
m
until it sta
r
ts to
evaporate o
r
sublim
e. In o
r
de
r to fo
rm
a film,
we
ne
ed to d
epo
sit
or
co
nden
se
that evapo
ra
tor
onto a
sub
s
t
r
ate surfa
c
e.
The mate
ria
l
whi
c
h is
u
s
ed
as
a so
urce melt
s i
n
to a liquid
and
sub
s
e
que
ntly starts to eva
porate into a
gaseou
s
vap
o
r or
sublim
e
s
. Evaporatio
n take
s pla
c
e
in a
vacuum if the
mean free p
a
th of atoms in the ev
aporate material i
n
that vacuu
m
spa
c
e is m
u
ch
longe
r than t
he dista
n
ce from the so
urce to t
he sub
s
trate. The He
rtz-K
nud
sen
equatio
n is u
s
ed
to express th
e rate of dep
osition.
∝
"
√
(
1
)
∂
N/
∂
t
= dep
osition rate from
a source
with surfa
c
e a
r
e
a
A
α
= coefficie
n
t
of evaporation
m = mole
cula
r weig
ht of the evaporate
k = Boltzm
an
n’s con
s
tant
T = tempe
r
at
ure
p"= vapo
r pre
s
sure at the e
v
aporate
su
rface
p = hydro
s
tati
c pre
s
su
re a
c
ting on the so
urce’s
su
rface [19]
Vacuu
m
eva
p
o
ration
i
s
ren
o
wn
ed
as a
l
o
w-ene
rgy
proce
s
s b
e
cau
s
e it requi
re
s v
e
ry little
kineti
c
ene
rg
y to conden
se the de
po
sited mate
ri
a
l
onto the substrate.
Mo
reove
r
, the film
depo
sition i
s
almost
strict
ly line of sig
h
t si
n
c
e the
vapor
con
d
e
n
se
s o
n
to the open
su
rfa
c
e
s
identical to it and doe
s not coat ed
g
e
s pe
rpe
ndi
cular to the source [20]. Film depo
siti
on
thickne
ss d
e
p
end
s on the q
uantity or rate
of gener
ated
vapor mate
ri
al and the di
stance from th
e
sou
r
ce to the
sub
s
trate. Rates g
r
e
a
tly rely on the
su
bstrate
to
so
urce g
eomet
ry as
well a
s
t
he
depo
sition rat
e
whi
c
h can vary
in
ca
se of
large
sub
s
t
r
ates
due to i
t
s stro
ng fun
c
tion of distan
ce.
The va
riation
in d
epo
sitio
n
rate
be
ca
u
s
e
of po
si
tio
n
rel
a
tive to
the source
can b
e
fou
n
d
by
Knudsen’
s co
sine l
a
w, cos
θ
/r
2
, whe
r
e r i
s
the radial
di
st
an
ce fro
m
the source
an
d
θ
is the
an
gle
betwe
en that
radial
vecto
r
and the
no
rm
al to the
re
cei
v
ing su
rfa
c
e.
The va
riation
of thickne
s
s
on
a coate
d
su
rface
whi
c
h is
cente
r
ed at a
distan
ce, h below o
r
abov
e a sou
r
ce ca
n be expre
ssed
by the followi
ng equ
ation:
1
/
(
2
)
Evaluation Warning : The document was created with Spire.PDF for Python.
ISSN: 23
02-4
046
TELKOM
NI
KA
Vol. 14, No. 2, May 2015 : 266 – 269
268
Whe
r
e,
t
o
= thickne
ss at the center
of the coated
surfa
c
e di
re
ct
ly above or b
e
low the
sou
r
ce.
t
x
= thickn
ess of depositio
n
at some di
stance,
x from the ce
nter of the co
ated surface.
The
sou
r
ce
can b
e
tre
a
ted
as a
point
so
urce if th
e
so
urces a
r
e ve
ry small i
n
co
mpari
s
o
n
to the sou
r
ce
to sub
s
trate d
i
stan
ce (h
). T
hen, the equ
a
t
ion can b
e
written as:
t
x
= t
o
(3)
Figure 1. Schematic illustra
tion of thickness [21]
3. Results a
nd Analy
s
is
Figure 2 an
d
3 sh
ows the
variation of resi
st
ivity and con
d
u
c
tivity
with differe
nt dopin
g
c
o
nc
en
tr
a
t
io
n o
f
In
2
O
3
respectively at 307 K. It is found fr
o
m
the grap
hs tha
t
the resi
stivity
decrea
s
e
s
wi
th incre
a
si
ng
the
dopin
g
con
c
e
n
tration
and
the
co
ndu
ctivity increa
se
s
with t
he
increa
se of dopin
g
con
c
entration. Th
e variati
on
of sheet re
sistan
ce with
different do
ping
c
o
nc
en
tr
a
t
io
n o
f
In
2
O
3
is
sho
w
n
in Fi
g
u
re
4. Th
e sheet
resi
stan
ce
also de
creases with t
he
increa
se of d
oping
con
c
e
n
t
ration. A
ll the data are give
n in table bel
ow.
Table 1. Data
for variation
of resi
stivity,
con
d
u
c
tivity a
nd sh
eet re
si
stan
ce with d
oping
c
o
nc
en
tr
a
t
io
n
Doping concentr
a
tion
in mole percent(
%
)
Resistivity
in (o
h
m
-cm)/1000
Conductivity
in(m
ho/cm)
Sheet resistance in (ohm). 10
00
25 43.12
24.10
4.15
30 11.99
82.99
0.99
40 7.69
129.10
0.70
Figure 2. Vari
ation of resi
st
ivity with doping
c
o
nc
en
tr
a
t
io
n o
f
In
2
O
3
doped Al
2
O
3
thin fil
m
Figure 3. Vari
ation of con
d
uctivity with doping
c
o
nc
en
tr
a
t
io
n o
f
In
2
O
3
doped Al
2
O
3
thin film
25
30
40
43.
12
11
.
9
9
7.
6
9
0
10
20
30
40
50
12
3
N
o
. o
f
s
a
m
p
le
Do
p
i
n
g
c
o
nc
e
n
t
r
at
i
o
n
in
mo
le
p
e
r
c
e
n
t
R
e
s
i
s
t
iv
it
y
in
(
O
h
m
-
c
m
)
/
1
000
25
30
40
24.
1
82
.
9
9
129
.
1
0
20
40
60
80
10
0
12
0
14
0
12
3
N
o
. o
f
s
a
mp
le
D
o
pi
ng
c
o
nc
en
t
r
at
i
o
n
in
mo
l
e
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TELKOM
NIKA
ISSN:
2302-4
046
Electri
c
al Pro
pertie
s
of Indium
Doped Al
um
ina (Al
2
O
3
) Thin Film
s (Had
aate Ulla
h)
269
Figure 4. Vari
ation of Shee
t Resi
st
an
ce
with dopi
ng concentratio
n
of In
2
O
3
dope
d Al
2
O
3
thin fil
m
4. Conclusio
n
In this p
ape
r
work
we
foun
d that the
co
ndu
ctivity of Al
2
O
3
incr
ea
s
e
s
wit
h
t
h
e
in
cre
a
s
e
s
of Indium do
ping con
c
ent
ration. On th
e other
h
and
, the resi
stivity and
the sheet re
si
stan
ce
decrea
s
e
with the increa
ses of
Indium dopin
g
co
nce
n
tration.
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