Microelectronic and micromechanical sensors and actuators in CMOS technology: A novel scheme towards regularization and integration

Present day integrated circuit (IC) as well as sensor technology stem from silicon microelectronic processing with one marked difference in their direction of progress. IC technology is being developed in the direction of commercial accessibility, while the sensor technology still relies upon customization of fabrication techniques and consequently its development is restricted to selected research groups. An attempt has been made to overcome this serious limitation by regularizing the microsensor fabrication scheme using a commercially well-established IC technology. A simple, yet powerful approach has emerged as a result of this attempt. Many inherent features of commercial CMOS technology have been identified and found to be ideally suited for microsensor fabrication. Based on these features, a special sensor layout design procedure has been introduced to achieve complete compatibility with the CMOS technology, without altering any of the CMOS process sequences. Under this scheme, fabrication of sensors and actuators has become possible in just two steps, namely layout design step and a single post-processing step. The approach leads to several advantages. First, the major obstacle for the progress of the sensor development is overcome by eliminating the requirement for customized fabrication facilities. Secondly, a direction has been set forth to regularize the sensor fabrication approach as it exists in today's integrated circuit technology. This implies that sensors and actuators of different kinds are realizable using a fixed technique. Thirdly, realization of integrated sensor systems with on-chip electronics becomes easily feasible since the circuit forming capabilities of the CMOS process remain unaffected in the entire scheme.;Several devices have been successfully fabricated and tested using this scheme. The devices include integrated humidity sensors and micromechanical structures such as bare polysilicon microbridges, sandwiched oxide microbridges, cantilevers and suspended plates. Functional devices such as electro-thermal gas flow sensors, thermal and visible radiation sources and electro-thermal microactuators have also been realized using the sandwiched oxide micromechanical structures. The on-chip circuit integration capabilities have been demonstrated by various designs and tests. The functioning of the fabricated devices has been studied systematically and the results are reported. A simple analytical scheme has been developed to model the thermally isolated micromechanical structures. Modeling results are compared with various experimental results.