7E-2 A De-Coupled Stacked Bulk Acoustic Resonator (DSBAR) Filter With 2 dB Bandwidth > 4%

Coupled resonator filters extend the use of classical FBAR/BAW filters by enabling them to convert single-ended signals into differential signals while using a much smaller wafer real estate. In lieu of the traditional multi-layer de-coupling structure we introduce a novel technique in which only a single thin polymer layer with appropriate acoustic impedance is used. In the de-coupled stacked bulk acoustic resonator design (DSBAR) we demonstrate a 0.4 x 0.5 mm single-ended filter operating at 2.45 GHz with a bandwidth at the 2 dB points of greater than 4%, in-band return loss of less than -10 dB and excellent out-of-band rejection. Cross-wafer variation and the temperature response of these filters are shown.