Development of Thin Film Common-mode Filter using MIM Capacitors and Coupled Inductor for UHF Band

Abstract

A thin film common-mode filter (CMF) for the cell phone at UHF band was fabricated and evaluated. The thin film CMF made by the thin-film technology, and it consisted of plural MIM capacitors and a coupled inductor. The authors fabricated two kinds of the thin film CMF for 0.70 - 1.0 GHz band and 1.8 - 2.0 GHz band. A size of the 0.70 - 1.0 GHz band type CMF is 1,140×1,260×10.5 µm³. On the other hand, a size of the 1.8 - 2.0 GHz band type CMF is 1,060×1,060×10.5 µm³. The volume of both thin film CMF is less than half of that of the commercial chip common-mode choke coil (CMC). In addition, both thin film CMFs has an insertion loss in differential mode less than 3 dB, and a common mode attenuation more than 28 dB at each band. Their characters are substantially equal to the characteristic of the commercial chip CMC.