Band 40
Fabrication and Operation of Fast, Ultra-low-power Gas Sensors with Carbon Nanotubes
Aus der Reihe
Scientific Reports on Micro and Nanosystems
-
- Englisch ausgewählt
64,00 €
inkl. gesetzl. MwSt.,
Beschreibung
Produktdetails
Einband
Taschenbuch
Erscheinungsdatum
19.12.2024
Herausgeber
Christofer HieroldVerlag
Hartung-GorreSeitenzahl
214
Maße (L/B/H)
24/17/1,4 cm
Gewicht
370 g
Auflage
2025
Sprache
Englisch
ISBN
978-3-86628-836-2
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.
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.
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