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How are semimetallic ceramic conductors used in thick-film microcircuits?

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conductive ceramics Figure 1: Schematic diagram of a zirconia oxygen sensor used to monitor automobile exhaust gases. The sensor, approximately the size of a spark plug, is fitted into the exhaust manifold of an automobile engine. The thimble-shaped zirconia sensor, sandwiched between thin layers of porous platinum, is exposed on its interior to outside air and on its exterior to exhaust gas passing through slits in the sensor shield. The two platinum surfaces serve as electrodes, conducting a voltage across the zirconia that varies according to the difference in oxygen content between the exhaust gas and the outside air.

Semimetallic ceramic conductors, such as ruthenium dioxide (RuO $_{2}$ ), bismuth ruthenate (Bi $_{2}$ Ru $_{2}$ O $_{7}$ ), and bismuth iridate (Bi $_{2}$ Ir $_{2}$ O $_{7}$ ), are utilized in thick-film microcircuits primarily as functional components for resistors.1

These materials are processed into "inks" by dispersing pulverized conductor particles and glaze into organic binders, which provide the necessary flow properties for screen printing. Once printed onto a substrate, the material is fired; during this process, the organic components burn away while the glazes fuse to form the final film.1

A key advantage of using these semimetallic ceramics is the ability to precisely control the electrical properties of the resulting components. By adjusting the ratio of conductor particles within the ink, manufacturers can produce a wide range of resistance values in the finished thick-film circuits. Because these ceramics possess overlapping electron energy bands, they function as excellent electronic conductors, similar to metals.1