Silicon Bulk Micromachined FBAR Filters for W-CDMA Applications

In this paper, fully integrated FBAR (Film Bulk Acoustic Wave Resonator) filters have been newly designed, fabricated, and characterized for W-CDMA mobile communication system applications by using silicon bulk micromachining technology. The proposed FBAR ladder type filters are realized by connecting 3 resonators in series and 4 resonators in parallel. The utilized resonators are comprised of aluminum nitride (AlN) piezoelectric material sandwiched by Mo electrodes on top of silicon nitride supporting membrane. The measured quality factor is 1530 at 1.9 GHz. The fabricated FBAR filters have insertion losses of -2.8 dB over the pass band, 0.5 dB ripple in pass band, absolute attenuation of 35 dB and 43 dB at 1.6 GHz to 1.875 GHz and 2.110 GHz to 2.170 GHz, respectively. They have the better performance characteristics than the conventional SAW (surface acoustic wave) filters. The actual die sizes of the fabricated FBAR filter are 1.2 mm × 1.4 mm before packaging and 3 mm × 3 mm after packaging, respectively.