FABRICATION COMPATIBILITY OF INTEGRATED SILICON SMART PHYSICAL SENSORS

Integrated silicon smart sensors are complete data-acquisition systems on a single silicon chip. The celebrated material compatibility of silicon sensors with microelectronic circuits in silicon is a necessary but insufficient prerequisite for such an integration. The essential issue is rather the fabrication compatibility of the sensor, sensor-related analog microelectronic circuits and digital interface circuits. Fabrication compatibility includes merging of sensor processing with analog and digital microelectronic circuit processing, both on the wafer level, in terms of doping profile, thermal budget and equipment utilization, and on the die level, with respect to testing, dicing, bonding and packaging. The incentives, opportunities and problems in merging sensor processes with a typical standard bipolar process are discussed. In some applications the structures to be merged are fundamentally fabrication incompatible. Special post-processing steps are available that either extend the capabilities of the bipolar process, such as selective epitaxial growth and epitaxial lateral overgrowth, or allow the fabrication-compatibility problem to be postponed until the bonding phase, such as wafer-to-wafer bonding and flip-chip bonding. Finally, the economics of integrated silicon smart sensors are investigated. The shortcomings of the conventional approach adopted from the microelectronics industry and aiming solely at die-area minimization, whenever possible for the sake of yield in mass production, are identified in view of fabrication compatibility, production volume and costs of testing and packaging. Moreover, the discrepancy between the prime motivation for fabricating integrated silicon smart sensors, namely enhancing the level of abstraction of the complete data-acquisition unit and its realization on the smallest possible material carrier, the chip, in order to improve user friendliness and maintainability in an effort to gain market acceptance, versus the limitation of functional complexity imposed by die-area economics is discussed.