Abstract
In this study, a resistive humidity sensor for moisture detection at room temperature is presented. The thin film proposed as a critical sensing element is based on a quaternary hybrid nanocomposite CNHox//SnO2/ZnO/PVP (oxidated carbon nanohorns–tin oxide–zinc oxide–polyvinylpyrrolidone) at the w/w/w/w ratios of 1.5/1/1/1 and 3/1/1/1. The sensing structure consists of a Si/SiO2 dielectric substrate and interdigitated transducers (IDT) electrodes, while the sensing film layer is deposited through the drop-casting method. Morphology and composition of the sensing layers were investigated through scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction, and Raman spectroscopy. Each quaternary hybrid nanocomposite-based thin film’s relative humidity (RH) sensing capability was analyzed by applying a direct current with known intensity between two electrodes and measuring the voltage difference when varying the RH from 0% to 100% in a humid nitrogen atmosphere. While the sensor with CNHox/SnO2/ZnO/PVP at 1.5/1/1/1 as the sensing layer has the better performance in terms of sensitivity, the structure employing CNHox//SnO2/ ZnO/PVP at 3/1/1/1 (mass ratio) as the sensing layer has a better performance in terms of linearity. The contribution of each component of the quaternary hybrid nanocomposites to the sensing performance is discussed in relation to their physical and chemical properties. Several alternative sensing mechanisms were taken into consideration and discussed. Based on the measured sensing results, we presume that the impact of the p-type semiconductor behavior of CNHox, in conjunction with the swelling of the hydrophilic polymer, is dominant and leads to the overall increasing resistance of the sensing film.
Highlights
In recent years, relative humidity (RH) sensors have been widely designed and developed due to their relevance in a large variety of industrial, commercial, and residential applications such as buildings heating, air conditioning and ventilating (HVAC systems), handheld devices, medical field, food processing, automotive industry, pharmaceutical processing, agriculture, diagnosis of corrosion and erosion in infrastructures and civil engineering, environmental and meteorological monitoring, mining industry, robotics and so forth. [1,2,3,4,5].Apart from the sensing principle, fabrication technologies, and sensor design, the materials used as sensing elements play a cardinal role in developing an RH sensor with superior performances [6]
A posite was investigated by scanning electron microscopy (SEM)
The experimentally measured RH sensing response of resistive sensors using sensing layers based on an organic–inorganic quaternary hybrid nanocomposite of CNHox/SnO2 /
Summary
Relative humidity (RH) sensors have been widely designed and developed due to their relevance in a large variety of industrial, commercial, and residential applications such as buildings heating, air conditioning and ventilating (HVAC systems), handheld devices, medical field (respirators, medical air lines, sterilizers), food processing, automotive industry (engine testbeds), pharmaceutical processing (storage, packaging, tablet coating, and compression), agriculture (soil moisture control, crop storage, conservation of seeds), diagnosis of corrosion and erosion in infrastructures and civil engineering, environmental and meteorological monitoring, mining industry, robotics and so forth. [1,2,3,4,5].Apart from the sensing principle, fabrication technologies, and sensor design, the materials used as sensing elements play a cardinal role in developing an RH sensor with superior performances [6]. Many different materials have been investigated as sensing layers within the design of RH sensors [7]. Due to their outstanding features, such as high sensitivity towards moisture, facile and versatile synthetic methods, low cost and tunable electric properties, as well as the ability to operate under severe conditions, semiconducting metal oxides (MOXs) have emerged as a promising choice in the RH sensor field [8].
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