Thin- film bulk acoustic wave resonators (FBAR), and heterogeneous integration with CMOS technology

The high impact of FBAR on radio-frequency and, most recently, on sensing systems has motivated to the development of integration processes or integrated the resonator with other systems. This means that the fabrication process should succeed in producing high-quality-factor resonators and, at the same time, in integrating FBARs with standard CMOS technologies. A method for performing wafer-level heterogeneous integration of the FBAR with a CMOS substrate was developed. According to this method, the fabrication of a floating FBAR above standard CMOS substrates has been achieved for the first time. This method was demonstrated by integrating FBARs on the commercial CMOS films of AMS035 and CNM25. On the application side, different FBAR-based sensor applications were implemented, the localized-mass detector being the most relevant, which has been demonstrated for the first time using bulk-acoustic to high-frequency resonators. The FBAR composites consist of a thin layer of barium strontium titanate (BST) that is sandwiched between two electrodes deposited on silicon-on-insulator (SOI) wafer. The BST layer, which has a strong electrostrictive effect, is used for electromechanical transduction by means of its voltage-induced piezoelectricity.

Resonator FBAR,resonance, BST, acoustics, CMOS