Sandwich-type ferromagnetic RF integrated inductor

The first demonstration of a sandwich-type ferromagnetic RF integrated spiral inductor for the 2-GHz range is reported. Two ferromagnetic CoNbZr films were set to sandwich the spiral in order to enhance the amount of magnetic flux linkage across the coil current. The stresses given from the insulator to the ferromagnetic film were studied. The inductance L of 7.9 nH and the qualify factor Q of 12.7 were obtained for a 200 μm×400 μm size four-turn rectangular spiral at f=2 GHz. The inductance was better than that of an air core of the same coil size by 19%, and the Q was better by 23%. Comparison with the on-top magnetic film type was also discussed