P-Type NiO Thin Films Prepared by Sputtering for Detection of Pollutants
NiO thin films were deposited by RF reactive magnetron sputtering and investigated in view of application as p-type material for sensing of pollutants. The thin films were deposited on Si-wafer, glass and alumina substrate using a nickel oxide target at v
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Introduction
Since the last five decades, semiconductor oxide materials are playing a big role in sensor industries, to detect harmful gases (CO, O3, H2S etc.) in petroleum industry, coal mine, etc. Still there are lots of challenges with MOX sensor like stability for the long time and sensitivity at the low temperature. On the other hand, these materials have great advantage in sensing field and have good detection probability with the target gases like ethanol (EtOH), H2, CO, O2 and acetone. During the last five decades, n-type semiconductor-based sensors were popular in the market and research field: metal oxides like ZnO, SnO2 and TiO2 were extensively investigated [1]. During the last two decades, p-type semiconductor oxide-based sensors have carved a niche in the sensor market and industries. We observed that p-type semiconductor oxides have good potentials for sensor application. Wisitsoraat et al. tested the NiO sensing layer for ethanol and CO and confirmed the p-type semiconductor oxide [2]. NiO can be a promising oxide for sensor application [4], which is naturally a p-type semiconductor oxide because of the oxygen ions vacancy. We investigated preparation conditions of NiO thin films by sputtering from a NiO target and investigated them by glancing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM) techniques. Gas sensing properties were studied as a function of preparation conditions with volt–amperometric techniques: the gas sensing properties towards CO, ethanol and NO2 are discussed.
R. Kumar • C. Baratto (*) • G. Faglia • G. Sberveglieri Department of Information Engineering, CNR-IDASC SENSOR Laboratory and University of Brescia, Via Valotti 9, 25133 Brescia, Italy e-mail: [email protected] E. Bontempi • L. Borgese INSTM and Chemistry for Technologies Laboratory, Department of Mechanical and Industrial Engineering, University of Brescia, Via Branze 38, 25133 Brescia, Italy C. Di Natale et al. (eds.), Sensors and Microsystems: Proceedings of the 17th National Conference, Brescia, Italy, 5-7 February 2013, Lecture Notes in Electrical Engineering 268, DOI 10.1007/978-3-319-00684-0_23, © Springer International Publishing Switzerland 2014
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Experimental
NiO thin films were deposited from a NiO target (99.99 % pure, 4″ size from CERAC) by RF reactive magnetron sputtering on different substrates: glass, silicon substrates for GIXRD tests and alumina 2 mm × 2 mm substrates for functional characterization as gas sensor. Deposition temperature of the substrate was varied from RT to 400 °C with step size of 100 °C in high vacuum (10−6 m bar) at 100 W powers. Ratio of O2/Ar was varied from 0, 10, 25 to 50 % for sensing film at 200 °C. The thickness of the layers was measured after deposition by a step profiler (Alpha step KLA TENCOR): the thickness of deposited films varied as a function of deposition time and sputtering conditions: thickness was 240–550 nm for thin films deposited on alumina for gas sensing tests and 220–580 nm for other tests. Ph
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