Abstract
Metal oxides (MOx) are a well-established material for gas sensing. MOx-based gas sensors are sensitive to a wide variety of gases. Furthermore, these materials can be applied for the fabrication of low-cost and -power consumption devices in mass production. The market of carbon dioxide (CO 2 ) gas sensors is mainly dominated by infra-red (IR)-based gas sensors. Only a few MOx materials show a sensitivity to CO 2 and so far, none of these materials have been integrated on CMOS platforms suitable for mass production. In this work, we report a cupric oxide (CuO) thin film-based gas sensor functionalized with gold (Au) nanoparticles, which exhibits exceptional sensitivity to CO 2 . The CuO-based gas sensors are fabricated by electron beam lithography, thermal evaporation and lift-off process to form patterned copper (Cu) structures. These structures are thermally oxidized to form a continuous CuO film. Gold nanoparticles are drop-coated on the CuO thin films to enhance their sensitivity towards CO 2 . The CuO thin films fabricated by this method are already sensitive to CO 2 ; however, the functionalization of the CuO film strongly increases the sensitivity of the base material. Compared to the pristine CuO thin film the Au functionalized CuO film shows at equal operation temperatures (300 ∘ C) an increase of sensitivity towards the same gas concentration (e.g., 2000 ppm CO 2 ) by a factor of 13. The process flow used to fabricate Au functionalized CuO gas sensors can be applied on CMOS platforms in specific post processing steps.
Highlights
Natural emissions of carbon dioxide CO2 in Earth’s atmosphere can be referenced to the carbon cycle
We present cupric oxide (CuO) thin film sensors fabricated by thermal oxidation of patterned copper layers
The evaluation of the gas sensitive copper oxide film was done by scanning electron microscopy (SEM) and Raman spectroscopy
Summary
Natural emissions of carbon dioxide CO2 in Earth’s atmosphere can be referenced to the carbon cycle. 4–6) to a value about 411 ppm [3]. Over the last two centuries the carbon dioxide concentration has risen from an average value of approximately 280 ppm [2] Apart from this alarming trend, CO2 has a significant direct impact to human health and plays an important role for indoor air quality monitoring. An elevated indoor CO2 level causes significant symptoms for humans: reduction of mental concentration, fatigue, headache, and dizziness [4].
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