High Efficiency Crumpled CNT Thin Film Heater For Hydrogen Sensing

Abstract

This paper presents the fabrication of crumpled carbon nanotube (C-CNT) thin film heaters and its application towards high sensitivity and low drift hydrogen gas sensing. By utilizing a simple spray coating of pristine multi-walled carbon nanotubes (MWCNTs) and thermal substrate shrinkage method, we have fabricated a C-CNT film with closely packed junctions. Joule heating of C-CNTs results higher temperature at a given input voltage compared to as-deposited CNTs. Specifically, the temperature of C-CNT heaters increase as high as 200 % than as-deposited CNT heaters due to higher junction densities in a given area. In addition, the temperature coefficient of resistance (TCR) of both C-CNT and as-deposited CNT heaters are analyzed for an accurate temperature control and measurement of the CNT heaters. All of the fabricated heaters exhibit linear TCR, and thus allowing a stable thermal operation. The higher heating efficiency of the C-CNT heaters can contribute to gas sensing with improved adsorption and desorption characteristics. Our results show that the C-CNT heaters are capable of hydrogen gas sensing while demonstrating higher measurement sensitivities along with lower drift compared to as-deposited CNT devices. Additionally, the self-heating mechanism of proposed heaters help rapid desorption of hydrogen, and thus allowing repetitive and stable sensor operation. Our findings reveal that both CNT morphologies and heating temperature affect the hydrogen sensing performances. The proposed C-CNT devices are suited for low power or voltage sensing platforms. For future work, sub-mm scaled shadow masks would allow C-CNT devices to be scaled down to µm-scale from macro-scaled devices. Hence, we envision the batch fabrication of C-CNT device arrays. In addition, C-CNT structures will be onto thermally resistant substrates, such as Silicon wafer, Glass or PET, so that we can compare C-CNT devices with as-deposited CNT on same substrate. Utilizing SEM micrographs and Raman analysis, the proposed transfer printing process will be optimized as well.