Hot plate gas sensors -: Are ceramics better

For modern gas sensors, low power consumption is expected. It is well known that with low temperature cofiring technology (LTCC) small compact sensors can be constructed. Compared with standard devices on alumina such sensors consume less power due to their lower thermal conductivity. However, simple replacement of substrate materials is not sufficient. LTCC offers the possibility to structure unfired tapes easily. Therefore, the sensor substrate may have almost any desired shape. In our first investigations, we showed that ceramic hot plates could be successfully constructed in LTCC technology. In contrast to standard configuration of thick-film gas sensors on alumina or even on LTCC, the hot plate principle allows to reduce significantly power consumption. Our tests showed possibilities to further decrease power consumption by laser forming of suspended beams. The obtained results were very promising and induced continuation of these works. This article shows recent results of investigations on hot plate structures. Tapes from different manufacturers have been used for sensor construction. The sensors were made by laser structuring of printed unfired LTCC tapes. Samples were evaluated by measurement and analysis of electrical properties as well as by long-term tests of integrated heaters. Design issues as well as stability issues are discussed in this contribution.