An Electrothermal Carbon Nanotube Gas Sensor

Abstract

We show both gas pressure and species sensing capabilities based on the electrothermal effect of a multiwalled carbon nanotube (MWCNT). Upon exposure to gaseous environments, the resistance of a heated MWCNT is found to change following the conductive heat-transfer variances of gas molecules. To realize this mechanism, a suspended MWCNT is constructed by synthesis and assembly in localized chemical vapor deposition that is accomplished within seconds via real-time electrical feedback control. Vacuum pressure sensitivity and gas species differentiability are observed and analyzed. Such MWCNT electrothermal sensors are compact, fast and reversible in responses, and fully integratable with microelectronics.Carbon nanotube (CNT) gas sensors based on fundamentally different mechanisms have been demonstrated, 1 including electrical conductance or capacitance changes 2-4 or using the sharp tips of the CNT as gas ionization sensors. 5 Limiting factors for sorption-based CNT sensors include low adsorption energies, diffusion kinetics, response speed, selectivity, and reversibility. We report on the electrothermal effect of a single multiwalled carbon nanotube (MWCNT) suspended between two silicon microbridges. When a Joule-heated MWCNT is exposed to different pressures, the electrical resistance change follows the conductive heat-transfer variances of gas molecules. The MWCNT is grown on silicon using the local synthesis method and is accomplished within tens of seconds via real-time electrical feedback control. Our findings suggest that the MWCNT electrothermal mechanism has applications to both gas sensing and species differentiation, with advantages of compactness, fast and reversible responses, low power consumption, and being fully integratable with microelectronics.The electrothermal gas sensing mechanism is schematically illustrated in Figure 1a. A single MWCNT is suspended between two silicon microstructures and heated by electrical current in the system. Energy conservation calls for total heat generation equal to the summation of heat conduction to the two microstructures (W C ), heat transfer via gases (W G , shown in the figure as W gas1 and W gas2 representing the case of two types of gases of different thermal conductivity values), and heat radiation (W R ). Both gas pressure and species can affect the heat-transfer process and result in MWCNT temperature changes and therefore resistance changes.To realize this architecture, we use a complementary metal oxide semiconductor (CMOS)-compatible, in situ controlled synthesis, assembly, and integration process previously reported in the literature. 6-9 Synthesis and assembly of carbon nanotubes has been heavily investigated with various device demonstrations using high-temperature synthesis processes 10,11 and labor-intensive assembly steps, 12,13 but assembly and heterogeneous integration of CNTs with microelectronics such as standard CMOS circuitry are still problematic. Many issues still need to be resolved, such as the synthesis and accurate placement...

Electrical response of Sm2O3-doped SnO2 to C2H2 and effect of humidity interference

“…Gas monitoring represents a growing demand driven by their applications in air quality control, environmental protection and healthcare as well as security [1][2][3][4][5]. Recently, sensitive gas sensors based on semiconductor oxides gain special interest due to their good reproducibility, compact size, ease of use, and low cost [6][7][8][9][10][11][12][13][14][15][16][17][18].…”

Suspended Carbon Nanotubes: Applications in Physical Sensors and Actuators

“…Kaul, 2009). A recent article by Kawano (Kawano et al, 2007) presents a sensing mechanism similar to that reported here, which utilized MWNTs grown using a localized synthesis process (Kawano et al, 2006). Here we report on the device application of sensors based on SWNTs that were grown using conventional thermal CVD.…”

Integration of Carbon Nanotubes in Microelectronics

“…Further, when a gas is injected in the vacuum chamber, fast CNTs cooling by the gas may result in a measurable current increase. This effect was first observed by Kawano et al, 2007. For suspended nanotubes (and attached nanoparticles), heating by Joule effect is much stronger, resulting in strong enhancement of chemical sensitivity to gas (oxygen).…”

“…The electrothermal mechanism is due to changes of the CNT electrical resistance (Kuo et al, 2007). Metallic MWCNTs can be self-heated considerably by current (in the way similar to NWs), and this leads to a rise of resistivity, with the temperature coefficient of resistivity (TCR) ~ 0.1% o C -1 (Kawano et al, 2007). Further, when a gas is injected in the vacuum chamber, fast CNTs cooling by the gas may result in a measurable current increase.…”