Pressure Sensor Elements Integrated with CMOS
J. Kiihamäki, T. Vehmas, T. Suni, A. Häärä, M. Ylimaula and J. Ruohio
VTT Information Technology, FI
MEMS, SOI, monolithical integration
We report the measurement and fabrication results of monolithically integrated capacitive pressure sensor elements. The device fabrication process is based on novel plug-up process, which enables monolithical integration of sensors and CMOS in a modular fashion. The capacitive sensors are made of the vacuum cavities embedded in SOI structure. The ambient pressure deflects the structure layer of the vacuum cavity in the sensor while the vented reference structure is not deflected. A self-made non-patterned SOI wafer was used as starting material. The substrate and structure layer doping level were selected to simultaneously obtain good sensor performance and to facilitate the CMOS fabrication. An extra pre-bond ion-implantation was performed to enhance the doping level in the bottom of the structure layer which is used as a top electrode of a capacitive sensor. The temperature sensitivity of sensors elements is excellent, limited by material properties of silicon and silicon dioxide. The electrical measurement results including pressure dependence, voltage dependencies of the various sensor geometries, and efects of the pre-bond tailoring of SOI wafers are presented in this paper.
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Nanotech 2005 Conference Program Abstract