A Switchless Quad Band Filter Bank Based on Ferroelectric BST FBARs

• Published in: IEEE microwave and wireless components letters Vol. 31; no. 6; pp. 662 - 665
• Main Authors: Nam, Suhyun, Koohi, Milad Zolfagharloo, Peng, Wenhao, Mortazawi, Amir
• Format: Journal Article
• Language: English
• Published: IEEE 01.06.2021
• Subjects: Barium strontium titanate (BST); bulk acoustic wave (BAW) filters; electrostriction; ferroelectrics; Film bulk acoustic resonators; filter bank; Filter banks; ladder-type filter; Matched filters; Microwave filters; reconfigurable systems; Resonator filters; Resonators; switchable; Switches
• ISSN: 1531-1309; 1558-1764
• DOI: 10.1109/LMWC.2021.3069880

An intrinsically switchable ferroelectric barium strontium titanate (Ba ( x ) Sr (1- x ) TiO 3 , BST)-based film bulk acoustic resonator (FBAR) quad channel filter bank is presented for the first time. The design incorporates a matching network free of tunable elements and provides a high isolation >30 dB across all four filter paths when the resonators are switched off. The measured insertion loss for the four 2.5 stage BST FBAR filters range from 6 to 7 dB with an out-of-band rejection >30 dB, which is an improvement over previously reported BST ladder-type structure. The filter bank, realized through T-networks, occupies an area of 840 <inline-formula> <tex-math notation="LaTeX">\mu \text {m} \times 340\,\,\mu \text{m} </tex-math></inline-formula> and operates across four different bands solely through the BST-based acoustic resonators.