Full integration of a pressure-sensor system into a standard BiCMOS process

We report a novel process for the full integration of surface-micromachined pressure-sensor cells into a standard BiCMOS process. Only the standard layers of the BiCMOS process are used to build up the sensor and only one additional photolithography step is necessary to achieve the micromachined structures. The application of the process is demonstrated by means of an integrated pressure-sensor system at a working range of 0.1 to 1.1 bar of absolute pressure. The influence of process parameters and tolerances of the VLSI process on the sensor performance are examined. To examine the long-term stability, the sensors are electrically deflected at the resonance frequency applying 4x10(11) load cycles. The measurements do not show any changes in the mechanical behaviour, so a very high long-term stability can be proven. In contrast to all integrated micromechanical systems presented so far, neither pre-nor post-processing of the system is necessary. Compared to conventional surface micromachining, the additional processing effort for the sensor realization is reduced dramatically to about 5% of the BiCMOS process. (C) 1998 Elsevier Science S.A. All rights reserved.