Ferroelectric thin-film-based electrically tunable bandpass filters

Abstract

We report on gold/Ba0.5Sr0.5TiO3 (BST) ferroelectric thin film C-band tunable bandpass filters (BPFs) designed and fabricated on magnesium oxide substrates using three different structures: microstrip, coplanar waveguide (CPW), and conductor backed coplanar waveguide (CBCPW). The two-pole filters were designed for a center frequency of 5.89, 5.88, or 5.69 GHz with bandwidths of 3, 9, or 7%, respectively. The BST-based CPW filter offers a higher sensitivity parameter as well as a lower loss parameter compared to the BST tunable two-pole microstrip filter and CBCPW filter. With an applied voltage of 40 V, the tuning range for the BPF with CPW structure was determined to be 170 MHz. (C) 2002 The Electrochemical Society.