Technologies Suitable for Gas Sensor Fabrication

Abstract

in gas sensors is one of the most important tasks of modern materials science. As shown in previous chapters, materials used in gas sensors need to ful fi ll a range of requirements related to the crystallographic structure, chemical composition , electrophysical properties, catalytic activity, and so on. These materials also show a great deal of variation. Materials for gas sensors can come in a variety of forms, including fi lms, ceramics, or powders. Their structure may be amorphous, glassy, nanocrystalline, polycrystal-line, single crystalline, or epitaxial. They may be either dense or porous. These materials may be elementary substances, complex compounds, or composites. Polymers, metals, dielectrics, and semiconductors can also be used as materials for chemical sensors. They may be either organic or inorganic in nature. This vast amount of variation indicates that it is impossible to produce such a wide range of materials using just one method. The possible differences in the physical-chemical properties of the materials are too great; so too are the resulting differences in the conditions required for the synthesis and deposition of these materials. Therefore, for preparing gas sensor materials with required properties we have to use various methods (see Fig. 28.1). These techniques differ in deposition rates, substrate temperature during deposition, precursor materials, the necessary equipment, expenditure, and the quality of the resulting fi lms. A short account of these methods is presented in Table 28.1. One can fi nd more detailed analysis of these methods in a vast array of quality reviews devoted to the subject (Brinker and Scherer 1990 ; It is clear that the selection of a method acceptable for sensor material synthesis or deposition during sensor design and fabrication is a complicated task, and we need to analyze many different factors, including the type of technology which will be used for sensor fabrication: ceramic, thick-fi lm, or thin-fi lm technologies. Of course, every technology has advantages and disadvantages. Tables 28.2 and 28.3 present a comparison of several of these methods. Limitations of technology based on the use of 1D nanomaterials (nanowires, nanotubes, etc.) were discussed in