Hartung-Gorre Verlag
Inh.: Dr.
Renate Gorre D-78465
Konstanz Fon: +49 (0)7533 97227 www.hartung-gorre.de
|
S
|
Scientific Reports on Micro and Nanosystems
edited by Christofer Hierold
Vol. 40
Seoho Jung
Fabrication and
Operation of
Fast, Ultra-low-power
Gas Sensors
with Carbon Nanotubes
1st Edition 2025. (8), XXVIII, 178 pages. € 64,00.
ISBN 978-3-86628-836-2
Abstract
The exceptional
properties of carbon nanotubes (CNTs), including their high mechanical
strength, electron mobility, and thermal conductivity, make them promising
candidates for various applications. One possible application is the sensing of
nitrogen dioxide (NO2), a toxic pollutant
with significant implications for air quality monitoring, pollution control, and
medical applications. Existing sensor technologies often fail to meet the stringent
requirements for power consumption, shelf life, readout speed, and limit of
detection (LOD) necessary for mobile applications. CNT-based gas sensors offer
substantial potential to address these limitations, yet several challenges must
be overcome to utilize their full potential.
One major technological
hurdle is the high-volume fabrication of CNT devices, in particular that of
suspended CNT devices, which demonstrate several advantages as sensors. This
thesis presents an approach to address this challenge, focusing on the scalable
batch growth of suspended CNTs and their automated assembly into functional
devices. Through systematic multi-parameter optimization and the development of
large-scale growth substrates, the optimal growth conditions for CNTs were
identified, leading to a significant increase in the number of individual CNTs
available for device integration. An automated nanoassembly
machine was employed to transfer pre-selected CNTs from growth substrates to
device substrates.
The process flow
designed around automated robotic assembly demonstrates a production rate –
mechanical transfer rate for carbon nanotubes – of approximately 46 CNTs per
hour, with a 70 % yield of electrically active devices. The assembled devices
were characterized electrically to understand the performance of devices
fabricated by this method.
Contact resistance at
the CNT-electrode interface is another critical factor influencing device performance.
This thesis demonstrates that electrode etching with argon ion immediately
prior to nanotube transfer effectively removes all adsorbates from palladium or
gold electrode surface and, as a result, consistently enables clean
CNT-electrode contact. When combined with post-transfer thermal annealing, this
pre-transfer treatment reduces the median ON-resistance (Ron) of CNT devices by an
order of magnitude and the interquartile range by more than two orders of
magnitude. This is crucial for the self-heating functionality of suspended CNT
gas sensors.
Lastly, the thesis
demonstrates the application of suspended CNTs in fast and ultra-low-power NO2 sensors. By leveraging self-heating for rapid gas desorption and
employing a nonlinear transient analysis method, the sensors achieved a signal
recovery time of 1 minute and readout time of 1-5 minutes at a peak power of
approximately 5.6 μW. With a readout time
of 5 minutes, the limit of detection of the sensor was 9 ppb NO2 in synthetic air with 40 % relative humidity. These performance
improvements were reproduced with additional devices, which were assembled both
manually and automatically.
Keywords: carbon nanotube (CNT), gas sensor, contact
engineering, nanostructure assembly, self-heating
Scientific Reports on Micro and Nanosystems
Direkt bestellen bei / to order directly from:
Hartung-Gorre
Verlag / D-78465 Konstanz / Germany
Telefon: +49 (0) 7533
97227
http://www.hartung-gorre.de
eMail: verlag@hartung-gorre.de