Japanese Journal of Applied Physics · 2008 · 70 citations · 4 references
EngineeringElectrical EngineeringMaterials ScienceAcousticsMicrowave EngineeringThin FilmsAcoustic MaterialsAcoustic Wave PropagationMicrowave FiltersMicrowave MaterialsAcoustic Band GapsAcoustic FiltersBandwidthFilm Bulk Acoustic ResonatorsFractional BandwidthInsertion LossInsertion Loss ReductionResonance
We have developed an X-band filter utilizing air-gap-type film bulk acoustic resonators (FBARs). The air-gap structure is simple and cost-effective. Results from both simulations and experiments demonstrate that a dome-shaped air gap was formed between the substrate surface and the bottom electrode and that an air-gap-type FBAR structure was possible. The air gap can be formed on the flat substrate using stress control of piezoelectric and metal films without using a thick sacrificial layer. As a result, the fabricated X-band FBAR operated successfully with a keff2 of 6.30%, a resonance Q of 246, and an antiresonance Q of 462. The fabricated filter had a center frequency of 9.07 GHz, a fractional bandwidth of 3.1% and a minimum insertion loss of 1.7 dB.
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