FULL INTEGRATION OF A PRESSURE-SENSOR SYSTEM INTO A STANDARD BICMOS PROCESS

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