Pressure Sensor Systems for Wide Pressure Ranges Integrated by a Combined CMOS- and MEMS- Technology

The demands on pressure sensors are multifaceted and requirements on their performances are steadily increasing because of rapidly growing applications fields. Concerning wide spread applications monolithic integrated pressure sensor systems based on the piezoresistive effect in silicon are favorable in most cases. Such systems are equipped with on-chip integrated signal processing and offer great flexibility for numerous detection purposes. Hence, these pressure systems are strongly demanded from the market. Having resilience in mind, their benefit is that no wire bonding between the sensing and circuitry components is required, and therefore, failure due to breaking bond wires is avoided. Since bond pads and a certain frame around the sensing membrane for assembly are omitted, the area around the membrane can be used for circuitry. In general such pressure sensor systems offer amplified output signals, which provide an enhanced robustness against electromagnetic compatibility (EMC) disturbances during transmission. Also calibrated output signals concerning sensitivity, linearity, and temperature dependent effects are usually provided. The fabrication of pressure sensor systems with on-chip integrated signal processing requires the application of two different technological approaches, which have to be co-integrated, i.e. CMOS technology for the electrical part and MEMS technology for the pressure sensor part. In the sequence of the technological fabrication process CMOS processing is performed first, then subsequent micromachining is employed for the membrane fabrication. Economic boundary conditions demand the fabrication of families of pressure sensor systems which cover as wide pressure ranges as possible with changeless lateral membrane geometry, since minimal mask numbers for the CMOS process are aspired. Another important point comes up, if integrated pressure sensors systems for automotive applications are considered. For such applications the CMOS part has to be processed in an automotive qualified standard process, which is very strict with regard to reliability. Changes in the CMOS part – caused for instance by are varying membrane geometry – would require a new process qualification, driving development costs often unacceptable high. Having this background in mind, our investigation was motivated by the extension of a commercial monolithic integrated pressure sensor family with onchip signal processing towards as wide pressure ranges as possible without changing the lateral pressure membrane geometry; off course, thickness variations of the membrane were possible. The development engineering was carried out in three steps, which were in parts recently separately published [1-3]. First the methodological approach was developed and verified for a sensor family covering four pressure ranges (0 – 1 AbstrAct1