Real metal oxide sensors

Important real world demands on a sensor array are selectivity and ability to distinguish substances of interest in a mixture. For the metal oxide sensor array the signature of a mixture appears to be the superposition of the signatures of its constituents, but, because the effect is exponential, the signature of the more reactive component will dominate. Therefore, if the substance that we seek to detect is the more reactive component, we will enjoy enhanced sensitivity (e.g. alcohol in gasoline). On the other hand, diluents such as alcohol can completely mask more subtle components such as essential oils. 

When working with sensors, one of the most important issues is cross-sensitivity. Due to the sensing principle, this notably affects metal oxide gas sensors, especially in the case of measurements performed in real life conditions. To prove real life feasibility, it is necessary to keep as close as possible to the real life conditions of the application. In the present case, the real life conditions are mainly represented by the use of ambient air as a carrier gas, but also by the chosen experimental set up. 

Baranzahi, A., Lloyd Spetz, A., Glavmo, M., Carlsson, C., Nytomt,X, Salomonsson, R, Jobson, E., Haggendal, B., Martensson,P. and Lundstrom,I. (1997),Response of metal-oxide-siUcon carbide sensors to simulated and real exhaust gases,5e sors... 

One real advantage of these sensors lies in the fact that an ion-selective membrane can act as a gate directly on a field effect transistor (FET) (Janata and Huber [1985]). These ion-selective field effect transistors (ISFET, shown schematically in Figure 4.3.2a) again are the analog of a solid state device, the metal oxide semiconductor field effect transistor (MOSFET, Figure 2.2.2b). 

Metal oxides and wide band semiconductors, such as SiC and GaN, with dielectric covering have a much better stability of surface and bulk properties in both oxygen and water environments in comparison with polymers and standard semiconductors (see Fig. 18.2), which prepares them for wide practical use in real devices of long-term use, available in the sensor market (Kerlau et al. 2006 Connolly et al. 2005). The results presented by Badwal (Badwal 1992 Badwal et al. 2000) show how stable metal oxides could be. Zirconia-based ceramics, which belong to the group of the most stable metal oxides, kept their electro-conductivity without considerable changes even at T> 1,000 °C. For comparison, the working temperature of polymer-based sensors is limited by 100-150 °C. 

Arbab A, Lloyd Spetz A, Lundstrom I (1993) Gas sensors for high temperature operation based on metal oxide silicon carbide (MOSiC) devices. Sens Actuators B Chem 15 19-23 Baranzahi A, Lloyd Spetz A, Glavmo M, Carlsson C, Nytomt J, Stilomonsson P, Jobson E, Haggendal B, Martensson P, Lundstrom I (1997) Response of metal-oxide-siUcon ctubide sensors to simulated and real exhaust gases. Sens Actuators B Chem 43 52-59... 

PM. Levine, P. Gong, R. Levicky, K.L. Shepard, Real-time, multiplexed electrochemical DNA detection using an active complementary metal-oxide-semiconductor biosensor array with integrated sensor electronics. Biosensors and Bioelectronics 24 (2009) 1995-2001. 

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