Dual band filter based on film bulk acoustic resonator

In this study, platinum (Pt) and zinc oxide (ZnO) had been adopted as electrode and piezoelectric layer of FBAR resonator. There are several types of filters, such as ladder-type, lattice-type and stacked couple filter, constructed from the FBAR resonator. The T-ladder type filter had been elected because of its high quality and simple fabrication processes. The pass-band width of filter is controlled by the mass loading on the specific resonator. The resonant frequency of FBAR is decided by the thickness of the piezoelectric layer. Due to the off-axis deposition, a dual mode resonance phenomenon is appeared. The precise mass loading is critical for the pass-band competition of longitude mode and shear mode in dual band filter. The frequency response is measured using an HP8720 network analyzer and a CASCADE probe station. The center frequency, 3-dB bandwidth, insertion loss and band rejection of longitude mode are 2353.125 MHz, 76.2 MHZ, -4.8066 dB and 7.1308 dB respectively. The center frequency, 3-dB bandwidth, insertion loss and band rejection of shear mode are 1044.375 MHz, 22.975 MHZ, -8.8314 dB and 1.5 dB respectively. The device has achieved and has a chance to apply in dual band wireless communication system.