Gas Sensor Devices based on CuO- and ZnO- Nanowires directly synthesized on silicon substrate
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Gas Sensor Devices based on CuO- and ZnO- Nanowires directly synthesized on silicon substrate R. Wimmer-Teubenbacher1, E. Lackner1, J. Krainer1, S. Steinhauer2, A. Koeck1 1 Materials for Microelectronics, Materials Center Leoben Forschung GmbH, Roseggerstrasse 12, 8700 Leoben, Austria 2 Okinawa Institute of Science and Technology (OIST) Graduate University, 1919-1 Onna-Son, Okinawa 904-0495, Japan ABSTRACT In-situ grown CuO and ZnO nanowire (NW) arrays were evaluated for their gas sensing performance. The metal structures were fabricated by standard e-beam lithography, thermal evaporation and lift-off process onto a silicon substrate with gold electrodes. After integration onto a test structure with resistive heater and thermocouple for temperature control, the samples were thermally oxidized at 400°C. During thermal oxidation, nanowires were grown between the oxidized metal structures. The gas sensing performance of the NW array was tested for carbon monoxide, - and a hydrocarbon-mixture (acetylene, ethane, ethene, and propene) at three relative humidity levels. INTRODUCTION The necessity for detection of harmful or lethal gases has led to a great variety of gas sensor schemes for indoor and outdoor air quality monitoring [1]. The efforts are directed towards finding a low-cost, low-power consuming gas sensor system with high sensitivity and selectivity, as well as with an easy fabrication process. Gas sensors based on metal oxides materials are good candidates to achieve these goals. Metal oxide gas sensing materials are employed in many different forms. Those relevant for application are films [2] , nanowires (NWs) [3], [4] and nanoparticles [5]. Metal oxide NWs can be used to fabricate single nanowire [4], NW network [6] or NW array devices [3]. Their primary advantage over thick or thin film gas sensing materials is their single crystalline nature, which produces lower base line drift of the sensor. Single NWs are mainly fabricated in a separate process from the deposition of the material itself. The routes for single NW synthesis range from vapor phase growth, solution phase growth [7] to solvothermal [8] and thermal oxidation [4]. After their synthesis, single NWs can be brought into any solution for deposition. The biggest drawback of devices based on a single NW is the complex procedure for the device fabrication (e.g. NW transfer onto a substrate). For the evaluation of single NWs, electrical contacts are either deposited on randomly oriented NWs or the NWs are aligned on fixed electrical contacts by the application of an external electric field [7]. As for thick or thin films, the evaluation of metal oxide single NWs is done at elevated temperatures generally by integration onto a microhotplate or by heating the single NW via the Joule effect. NW networks can be fabricated by depositing numerous single NWs from solution onto a set of electrodes [6]. In this case, no alignment of the NWs is necessary. This vast network of NWs provides a large surface for gas sensing. In contrast to a single NW device the e
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