Electrode Materials Preferable for Gas Sensor Applications

Source Reprinted with permission from Furjes et al. (2002). Copyright 

In the case of micro-ho lates fabrication using micromachining technology, we have a more complicated situation because, as well as the thermodynamic stability of the materials used, we need to take into account the compatibility of these materials with silicon technology. A more detailed analysis of electrode materials acceptable for micro-hotplates fabrication was carried out by Furjes et al. (2002). Materials acceptable for realization of micro-hotplates are presented in Table 9.1. 

Shim et al. (2011) have shown that conductive metal oxides can also be used as electrode materials in gas sensors. Analyzing the behavior of indium-tin oxide (ITO) and aluminum-doped zinc oxide (AZO) films in WO3- and SnO -based sensors, they established that ITO can replace Pt electrodes in these devices. Upon exposure to 50 ppm CO at 300 °C, WO3 or SnO thin-film sensors with ITO interdigitated electrodes (IDEs) on glass substrates displayed higher responses than sensors with Pt IDEs, attributed to the low-resistance ohmic contacts between the electrode (ITO) and the sensing material (WO3 or SnO ). It is necessary only to take into account that contacts should be stabilized at T 500 °C before using ITO (see Fig. 9.4). 

Of course, in the case of gas sensors operated at room temperature we do not have such strong requirements from electrode materials, and therefore other materials, which are not as stable as Pt, can be used. In particular, gold (front and back) electrodes are used in most conventional QCMs. Other electrode materials such as aluminum, copper, silver, chromium, nickel, titanium, tungsten, zinc, as well as carbon and sihcon can also be used in gas sensors (ICM, htq //www.icmfg.com/crystalsJitml). 

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