Packaging of physical sensors for aggressive media applications

Micromechanical sensing elements have a high potential for a variety of applications detecting various properties. To date the commercial success has been essentially limited to pressure and acceleration detection. To extend the range of applications we believe the critical hurdle is to develop packaging schemes that ensure reliability and reduce packaging costs. For sensing in aggressive media, sensor packaging can be carried out at various levels. Packaging attempts are critically discussed and compared. The discussion is exemplified by using pressure sensors since this is the only sensor type at a sufficiently mature level of development. In particular a packaging scheme using protective thin films, mounting the sensing element in direct contact with the media, is discussed. Limitations on the traditional materials in chip processing are presented, concluding that the chemical stability is inadequate.