Biomedical Engineering Reference
In-Depth Information
gas sensor based on CNT
array fabricated by dielectrophoretic method. It was reported a
detection limit of 50 ppb level operating at room temperature. The
CNTs were deposited onto Pt-equipped SiO
Lee
et al
. [264] demonstrated a NO
2
-coated wafer substrate.
The bias voltage modulation improved the sensor performance by
controlling the Schottky barrier potential. This device is highly NO
2
2
sensitive at room temperature, which may benefit to reduce the
fabrication steps and cost, as claimed by the authors.
SWCNT-based
gas sensor fabricated by dielectrophoretic process on electrodes
structure. It was found that ammonia decreases the electrical
conductivity caused by the electron transfer to the SWCNT layer,
while nitrogen dioxide induced an opposite effect in the sensor
response. Special geometry was designed with a back-gate third
electrode in the sensor structure to accelerate dramatically the gas
adsorption and desorption phenomena with an enhanced response
time and recovery time.
Lucci
et al
. [266] demonstrated NO
and NH
x
3
. [149] demonstrated an oxygen-treatment
functionalized MWCNT sensor fabricated onto a microhotplate silicon
substrate. An oxygen-based RF-plasma was inductively coupled to
MWCNT layers. XPS studies showed that the chemical composition
of the nanotube surface depends on the plasma conditions used
in the oxygen-plasma treatment. The treated MWCNTs were then
deposited by drop-coating method onto microhotplate sensor. A
well-adhered thick film of CNT mesh (
Ionescu
et
al
m) was achieved after
annealing in air. The influence of the various plasma conditions on
the response of gas sensors fabricated by functionalized MWCNT
coating was studied. The gas sensing properties were investigated
both experimentally and theoretically for NO
~
17
µ
gases, at
room temperature. Figure 9.30 shows the scheme of MWCNTs
microhotplate sensor and the device of CNT array based on drop-
coated MWCNTs. The best response toward NO
and NH
2
3
gas was found for
sensors coated with MWCNT films plasma-treated (RF power: 30 W;
work pressure: 0.1 Torr; treatment time: 30 min; oxygen-plasma:
20%) and subsequently annealed in situ at 350°C for 2 h, which
exhibited highest concentration of C=O functional groups. Therefore,
these functional groups played a key role in the sensitivity to nitrogen
dioxide species. These sensors operating at room temperature were
able to detect NO
2
gas at concentrations as low as 500 ppb. In the
contrast, the best sensitivity toward NH
2
gas was achieved at room
3
