Design and measurement of integrated inductors using high-frequency magnetic films

Driven by the fast-growing market for wireless communications, a strong inter-est in integration of inductors operating at high-frequencies has developed. But traditional problems such as low self-resonant frequencies still retard such development. In this thesis, the use of a magnetic material with good high-frequency permeability (μ) is considered as a means by which to improve the inductance performance. Further, to reduce the eddy-current power loss in the magnetic materials, lamination is investigated. Various structures of integrated inductors were designed by using a 3-D electromagnetic simulator, Maxwell. A number of case studies were carried out on bars, single-layer spiral structures and double-layer spiral structures, in terms of inductance and eddy power loss at 1 GHz. Moreover, stray capacitances and fabrication feasibility were also taken into consideration. Four new material-wrapping methods were proposed and studied. As a result of these case studies, one single-layer spiral inductor and two double-layer spiral inductors have been proposed. Their inductances were found to range from 970 nH to 2680 nH in an area of 450 μm by 450 μm and their Q-factors at 1 GHz were estimated to range from 87 to 141. Soft magnetic materials with high-frequency properties were also discussed. Multilayer magnetic materials having some properties not available in single-layer structure which favour the high-frequency application of inductors are considered. A variety of magnetic materials, namely Co80Zr10Nb10/ SiO2, NiFe/SiO2, (Fe/SiO2)SiO2 and CoFe/SiO2 multilayers were considered for use in fabricating the integrated inductors. Advantages of AlN over SiO2 as a non-magnetic insulator were presented and explained. Finally, a number of permeability measurement techniques for soft magnetic materials at high-frequencies were discussed. The "Magnetic (M)/Conductive (C)/Magnetic (M) layers inductance-line" method was found to be the most suitable. Key issues in fabricating material testing unit were presented and solved. It was revealed that the lift-off process is an effective method for patterning multilayer magnetic materials. A permeability of about 300 was maintained for frequencies close to 650 MHz for CoNbZr/SiO2 film. Overall, a blueprint for the fabrication and characterization of potential integrated inductors is presented