In the early phase of MEMS development piezoresistive pressure transducers were dominating due to their simple fabrication technology. However, recently there is a trend to surface micromachined capacitive absolute pressure sensors. Due to their compatibility to CMOS process the devices are predestinated for monolithic integration of signal conditioning electronics. The pressure range is design controlled by adjusting the diameter of the sensor diaphragm, keeping the thickness to be fixed. This allows the fabrication of various sensors for low ( 1 bar max.) up to high (350 bar max.) pressure ranges on a same wafer. Additional advantages are high overpressure stability, small chip size and low power consumption, allowing the sensors to be used in transponder applications and as medical implants. Based on our former work on capacitive absolute pressure sensors the capacitive differential pressure sensors were developed. In contrast to the absolute pressure sensor elements with hermetically vacuum sealed cavity the differential pressure sensor elements are accessible to media from both sides of the polysilicon diaphragm. An optional version with a vent on the front side of the chip was added to our initial approach with a venting capillary fabricated from the backside.
