Characterization of UHF Band LC Filter With RF Spiral Inductor Using Carbonyl-Iron Powder/Epoxy Composite Magnetic and Chip Capacitor

In order to realize the Q-factor increase scheme for a radio frequency (RF) spiral inductor used in the RF front/end circuit of smart phone handset, an introduction of carbonyl-iron powder (CIP)/epoxy composite magnetic core to air-core spiral inductor has been done. The composite magnetic core made by metal-mask printing consisted of 1.1 μm mean diameter CIP and epoxy resin matrix. A two-turn copper spiral inductor with composite magnetic core filled only in spacing between conductor lines was fabricated. The Q-factor of the inductor with composite magnetic core is about 1.3 times higher than that of an air-core spiral inductor at around 0.7 GHz. An important effect of Q-factor increase by embedded composite magnetic core in the spacing between conductor lines is obtained. A main reason is that a proximity effect is suppressed in conductor line of the spiral coil. In addition, the simplest LC filter simulating RF circuit with the RF spiral inductor using the composite and a chip capacitor was fabricated and evaluated. The transmission coefficient of the composite magnetic core spiral inductor was about 0.9 times lower than that of the same size air-core spiral inductor. The filter characteristic of the composite core inductor was superior to that of the air-core inductor.