An Intrinsically Switchable Balanced Ferroelectric FBAR Filter at 2 GHz

An intrinsically switchable balanced lattice-ladder ferroelectric thin film bulk acoustic resonator (FBAR) filter is presented for the first time. A 1.5 stage balanced ladder-type filter and a 2-pole lattice-type filter with a center frequency at 2 GHz are first designed through the image parameter method. Subsequently, the filters are connected in series to form a ladder-lattice filter and fabricated based on ferroelectric barium strontium titanate (BST) FBARs. The measured two-section balanced filter provides a high out-of-band rejection and OFF-state isolation levels of more than 40 dB with a sharp roll-off.