Specificity, sensor design

Analytical chemistry in the new millennium will continue to develop greater degrees of sophistication. The use of automation, especially involving robots, for routine work will increase and the role of ever more powerful computers and software, such as intelligent expert systems, will be a dominant factor. Extreme miniaturisation of techniques (the analytical laboratory on a chip ) and sensors designed for specific tasks will make a big impact. Despite such advances, the importance of, and the need for, trained analytical chemists is set to continue into the foreseeable future and it is vital that universities and colleges play a full part in the provision of relevant courses of study. 

Several papers have been published in which, instead of concentrating on specific reactions, the technology was highlighted. One, by Marose et al.,7 discusses the various optics, fiber optics, and the probe designs that allow in situ monitoring. They describe the various optical density probes used for biomass determination in situ microscopy, optical biosensors, and specific sensors such as NIR and fluorescence. 

The central topic of the book was the integration of microhotplate-based metal-oxide gas sensors with the associated circuitry to arrive at single-chip systems. Innovative microhotplate designs, dedicated post-CMOS micromachining steps, and novel system architectures have been developed to reach this goal. The book includes a multitude of building blocks for an application-specific sensor system design based on a modular approach. 

A further interesting effect discovered in our laboratories is that the addition of low levels of a second component, or dopant ion, can lead to significant increases in the ionic conductivity [6, 30, 31]. Typically these dopant species, for example, Li, OH , and H" ", are much smaller than the organic ions of the matrix, and since the relaxation times characterizing the motion of these ions are more rapid than those of the bulk matrix itself, these materials may represent a new class of fast ion conductor. The dopant ion effect can be used to design materials for specific applications, for example, Li+ for lithium batteries and H /OH for fuel cells or other specific sensor applications. Finally, we have recently discovered that this dopant effect can also be apphed to molecular plastic crystals such as succinonitrile [32]. Such materials have the added advantage that the ionic conductivity is purely a result of the dopant ions and not of the solvent matrix itself. 

Despite the fact that the mathematics of the statistical methods for the control experiments of reliability testing is well developed, the sensors designer usually has difficulties with considering specific test methods for the reliabihty testing applicable to various zirconia-based gas sensors. 

The topics of subsequent sections are the different materials used for thin films, specifically, silicon oxide (Section 5.5.3), silicon nitride (Section 5.5.4), poly-silicon (Section 5.5.5), and other materials, such as metals and silicon oxynitride, as well as novel thin film materials that may appear in future sensor designs (Section 5.5.6). In these sections, we adhere to the following structure first, the basic deposition process is briefly described, followed by the common function of the layer in sensor design. Subsequently, we discuss in detail the important material properties. 

The accuracy and reliability of microsensors under severe environmental conditions are of prime importance in automotive applications. To meet the required quality at competitive cost levels, high yields within the product specifications have to be ensured under conditions of high-volume production. In addition to the continuous development of refined sensor designs and processing technologies, appropriate testing concepts and methods are indispensable to guaranteeing specified quality and sustained economic success. 

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