Acoustic-wave based monolithic microsensors

Acoustic-wave based oscillators are used for several sensor applications. In addition to crystalline piezoelectric materials, silicon has gained interest as a substrate material for acoustic devices. Silicon implemented acoustic devices profit from the excellent properties of the silicon integrated circuit (IC) technology: high reliability, high reproducibility, small size and low cost. The monolithic integration of electronic circuitry and acoustic devices allows the development of highly-reliable small-size acoustic oscillators for sensor applications. In this paper the design and fabrication of monolithic Lamb wave oscillators is presented. In addition to bipolar IC-technology extra processing is required to obtain the Lamb wave oscillator system: thin film piezoelectric zinc oxide technology, and micromachining technology. The technologies used are completely IC-compatible which is an important feature for commercial production. The system forms the basis for several measurement instruments, e.g. liquid process-control equipment (control of composition of mixtures, determination of density and viscosity) and biosensors