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Issue 12, 2018, Issue in Progress
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ppb level detection of NO2 using a WO3 thin film-based sensor: material optimization, device fabrication and packaging

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Abstract

In this study, we have investigated the thickness-dependent nitrogen dioxide (NO2) sensing characteristics of a reactive-ion magnetron sputtered tungsten trioxide (WO3) film, followed by morphological and electrical characterizations. Subsequently, the sensing material was integrated with an MEMS platform to develop a sensor chip to integrate with electronics for portable applications. Sputtered films are studied for their sensing performance under different operating conditions to discover the optimum thickness of the film for integrating it with a CMOS platform. The optimized film thickness of ∼85 nm shows the 16 ppb lower limit of detection and 39 ppb detection precision at the optimum 150 °C operating temperature. The film exhibits an extremely high sensor response [(RgRa)/Ra × 100 = 26%] to a low (16 ppb) NO2 concentration, which is a comparatively high response reported to date among reactively sputtered films. Moreover, this optimum film has a longer recovery time than others. Thus, an intentional temperature overshoot is made part of the sensing protocol to desorb the NO2 species from the film surface, resulting in full recovery to the baseline without affecting the sensing material properties. Finally, the optimized film was successfully integrated on the sensor platform, which had a chip size of 1 mm2, with an inbuilt micro-heater. The minimum power consumption of the microheater is ∼6.6 mW (∼150 °C), which is practically acceptable. Later, the sensor device was packaged on a Kovar heater for the detailed electrical and sensing characterizations. This study suggests that optimization of the sensing material and optimum operating temperature help to develop a highly sensitive, selective, stable, and portable gas sensor for indoor or outdoor applications.

Graphical abstract: ppb level detection of NO2 using a WO3 thin film-based sensor: material optimization, device fabrication and packaging

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Publication details

The article was received on 26 Dec 2017, accepted on 29 Jan 2018 and first published on 09 Feb 2018


Article type: Paper
DOI: 10.1039/C7RA13659E
Citation: RSC Adv., 2018,8, 6590-6599
  • Open access: Creative Commons BY license
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    ppb level detection of NO2 using a WO3 thin film-based sensor: material optimization, device fabrication and packaging

    C. S. Prajapati and N. Bhat, RSC Adv., 2018, 8, 6590
    DOI: 10.1039/C7RA13659E

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