Mobile-communications systems have inspired the increasing development of high-dielectricconstant (K) microwave substrates. With a bandpass filter fabricated on a high-K piezoelectric substrate using an interdigital capacitor and bond-wire inductor, researchers hope to eliminate the inductive effect of wire bonds. The individuals behind this effort are: Min-Hang Weng from Taiwanâ??s National Nano Device Laboratories; Ru-Yuan Yang from National Ping-Tung University of Science and Technology, Taiwan; Sean Wu and Cheng-Yuan Hung from Taiwanâ??s Tung-Fang Institute of Technology; and Shih-Bin Jhong from the National Kaohsiung University of Applied Sciences, Taiwan.

The lead-free piezoelectric substrate of bismuth sodium titanate ceramic was prepared by a conventional solid-state reaction method. The filter allows the resonant frequency to be controlled by varying the lengths of silver bonding wire in the packing process. The fabricated filter has a center frequency of 0.9 GHz, fractional bandwidth of 31.53 percent, maximum insertion loss of 1.66 dB, and minimum return loss of 17.2 dB. It also has two transmission zeroes at 0.24 and 2.45 GHz. See â??A Microwave Filter Fabricated on the Lead-Free Piezoelectric Substrate Using the Interdigital Capacitor and Bonding-Wire Inductor,â?쳌 Microwave and Optical Technology Letters, October 2008, p. 2594.