Sensors
and
Actuators
B
166–
167 (2012) 451–
456
Contents
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at
SciVerse
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Sensors
and
Actuators
B:
Chemical
journa
l
h
o
mepage:
www.elsevier.com/locate/snb
Capacitive
humidity
sensing
properties
of
SiC
nanowires
grown
on
silicon
nanoporous
pillar
array
Hai
Yan
Wang
a,b
,
Yong
Qiang
Wang
a
,
Qing
Fei
Hu
a
,
Xin
Jian
Li
a,∗
a
Department
of
Physics
and
Laboratory
of
Materials
Physics,
Zhengzhou
University,
Zhengzhou
450052,
People’s
Republic
of
China
b
Department
of
Technological
Physics,
Zhengzhou
University
of
Light
Industry,
Zhengzhou
450002,
People’s
Republic
of
China
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
10
June
2011
Received
in
revised
form
7
February
2012
Accepted
28
February
2012
Available online 5 March 2012
Keywords:
SiC
nanowires
Silicon
nanoporous
pillar
array
(Si-NPA)
Capacitive
humidity
sensor
Catalyst-assisted
chemical
vapor
deposition
a
b
s
t
r
a
c
t
A
large
quantity
of
entangled
SiC
nanowires
(nw-SiC)
with
an
average
diameter
of
∼15
nm
were
grown
on
a
silicon
nanoporous
pillar
array
(Si-NPA)
by
a
catalyst-assisted
chemical
vapor
deposition
method.
The
room-temperature
capacitive
humidity
sensing
properties
of
nw-SiC/Si-NPA
were
studied
by
evaporating
coplanar
interdigital
silver
electrodes
onto
its
surface.
With
the
relative
humidity
(RH)
changing
from
11%
to
95%,
a
capacitance
increment
over
960%
was
achieved
at
the
measuring
frequency
of
100
Hz.
The
response
and
recovery
times
were
measured
to
be
∼105
and
85
s,
respectively,
with
a
maximum
humidity
hysteresis
of
4.5%
at
75%
RH.
The
humidity
sensor
was
also
proved
to
be
with
high
measurement
reproducibility
and
long-term
stability.
Our
results
indicate
that
one-dimensional
SiC
materials
might
be
competitive
as
a
novel
sensing
material
for
fabricating
humidity
sensors
with
high
performances.
© 2012 Elsevier B.V. All rights reserved.
1.
Introduction
Compared
with
the
narrow-bandgap
of
∼1.12
eV
for
single
crystal
silicon
(sc-Si),
all
silicon
carbide
(SiC)
polytypes
are
wide-
bandgap
semiconductors,
such
as
∼3.2
eV
for
4H-SiC
and
∼2.4
eV
for
3C-SiC
[1].
The
properties
of
high
thermal
and
chemical
stability
make
SiC
being
more
suitable
than
sc-Si
for
fabricating
electronic
devices
to
be
operated
at
high
temperature
or
in
harsh
chemical
environment
[2].
In
the
past
years,
gas
sensors
based
on
porous
SiC
have
been
broadly
studied
for
monitoring
harmful
exhaust
gases
produced
from
industrial
processes
or
by
cars
[3–10],
and
improved
sensing
performances
including
relatively
rapid
response
speed
[3,4],
high
sensitivity
[4–6],
good
selectivity
[6–8]
and
long-term
stability
[8–10]
have
been
demonstrated.
Usually,
SiC-based
gas
sensors
were
constructed
as
Schottky
diodes,
field
effect
transistors
or
capacitor
systems
using
SiC
as
a
dielectric
material
[5,11,12],
by
which
gas
concentrations
were
determined
by
measuring
the
vari-
ation
of
the
electrical
current
or
capacitance
when
gas
molecules
were
adsorbed
on
the
surface
of
the
active
materials.
Among
the
sensors
with
various
device
structures,
capacitive
sensors
are
more
competitive
in
view
of
its
relatively
simple
manufacturing
proce-
dure
and
low
fabrication
cost.
Compared
with
the
study
on
bulk
SiC,
one-dimensional
SiC
(1D
SiC),
such
as
nanowhiskers
[13],
nanowires
[14–16]
and
nanorods
[17,18],
are
arousing
extensive
attention
in
recent
years
for
the
∗
Corresponding
author.
Tel.:
+86
371
67766629;
fax:
+86
371
67766629.
E-mail
address:
lixj@zzu.edu.cn
(X.J.
Li).
enhanced
physical
properties
brought
by
its
large
specific
area,
high
aspect
ratio
and
easy
occurrence
of
quantum
confinement
effects.
For
example,
strong
field
emission
[15,16,18]
and
photolumines-
cence
[14,17]
have
been
demonstrated
by
1D
SiC.
Considering
from
the
structural
and
physical
features
of
1D
SiC,
it
might
also
be
an
excellent
active
material
for
gas
sensors,
especially
for
those
being
operated
at
high
temperature
or
in
harsh
environment.
In
the
previous
study,
we
have
reported
the
preparation
of
sili-
con
nanoporous
pillar
array
(Si-NPA),
a
silicon
micron-nanometer
structural
composite
system
characterized
by
its
regular
arrayed
and
nanoporous
silicon
pillars
[19].
Utilizing
Si-NPA
or
its
nanocomposite
systems
as
sensing
media,
several
kinds
of
humid-
ity
or
gas
sensors
with
high
sensitivity,
short
response/recovery
times
and
small
hysteresis
were
prepared
[20–23].
These
results
indicate
that
Si-NPA
is
a
potential
system
both
as
a
direct
sensing
material
and
a
template
for
growing
other
sensing
materials.
In
this
article,
we
report
that
by
a
catalyst-assisted
chemical
vapor
depo-
sition
(CVD)
method,
large
quantities
of
SiC
nanowires
(nw-SiC)
were
grown
on
Si-NPA.
The
morphology
and
the
microstructure
of
nw-SiC/Si-NPA
were
characterized
and
its
capacitive
humid-
ity
sensing
properties
were
measured.
Based
on
the
experimental
data,
the
sensing
mechanism
was
analyzed.
Our
results
indicate
that
nw-SiC/Si-NPA
might
be
a
candidate
material
for
preparing
high-performance
silicon-based
capacitive
humidity
sensors.
2.
Experimental
details
The
preparation
of
Si-NPA
has
been
reported
previously
else-
where
[19].
In
the
present
experiment,
a
thin
layer
of
nickel
film,
0925-4005/$
–
see
front
matter ©
2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.snb.2012.02.087