X-BAND THIN-FILM ACOUSTIC FILTERS ON GAAS

The Semiconductor Bulk Acoustic Resonator (SBAR) is composed entirely of thin films, piezoelectric aluminum nitride (AlN) and metal electrod e films (primarily aluminum). It is fabricated on gallium arsenide (Ga As) wafers by depositing the thin film layers on top of the wafer and then etching away the GaAs from below, leaving a thin membrane support ed by its edges. SBAR resonators and filters can be fabricated as part of the HBT or MESFET Monolithic Microwave Integrated Circuit (MMIC) p rocesses, offering the high selectivity associated with acoustic reson ators and filters to the MMIC designer. This paper describes performan ce of a recent 1-pole SBAR filter which has only 6.1 dB insertion loss at 7.8 GHz (2nd harmonic) and 7.5 dB insertion loss at 11.6 GHz (thir d harmonic), with fractional bandwidths less than 1%. Also described a re 2-pole (1.4% bandwidth) and 4-pole (1.8% bandwidth) Chebyshev monol ithic SBAR filters at 2.4 GHz, demonstrating flat passbands and good r ejection. These results demonstrate that SBAR technology is practical for monolithic filters in MMICs at frequencies up to X-band.