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This paper examines the process challenges in developing high aspect-ratio copper structures for improving microinductor performance. With increased miniaturization, increasing windings losses become a major challenge limiting the microinductor efficiency. It was also identified that within constraint footprints coil thickness to spacing ratio increase can reduce dc resistance significantly. In this paper, we present a reliable process for developing high aspect ratio ( $\sim 5.8$ ) resist moulds for copper electrodeposition. This resist provided coil spacings 10 $\mu $ m for 58 $\mu $ m resist thickness; this in turn reduces the dc resistance of a typical microinductor by more than 17% when compared with a similar device reported previously. [ABSTRACT FROM AUTHOR]

In an integrated power microinductor, the size and shape of the magnetic material will have a relationship to the permeability and inductance of the device. To demonstrate these effects, a set of inductors with closed Ni45Fe55 films were fabricated having similar structures but different footprint sizes and aspect ratios (ARs). Magnetic and electrical characterization was performed on the devices to determine magnetic properties, and in both measurements the same relationship between film shape and magnetic anisotropy is observed. Micromagnetic shape anisotropy simulations were used to predict this behavior and correlate with the experimentally determined parameters. The AR of the film is determined to have a strong influence on the anisotropy and permeability of the magnetic film via shape demagnetization effects which is shown to be a significant variation from the as-deposited magnetic material parameters. [ABSTRACT FROM AUTHOR]

What is the future of integrated inductor design on silicon for power conversion applications at frequencies up to 100 MHz—is it magnetic-core or air-core inductors. This study presents measured results for two microfabricated inductors (magnetic core and air core), which have been designed to operate at 20 MHz and occupy a substrate area of less than 10 mm^2. The inductor technology and design are briefly discussed. An optimized inductor design study is, then, presented. Both magnetic-core and air-core inductor designs are compared and evaluated, in terms of inductance and efficiency per unit area for frequencies up to 100 MHz. The design of the microinductors is discussed and an analytical design optimization program is used to model the devices for the maximum efficiency and inductance. The introduction of laminations with high-frequency core inductors will also be examined within the study. A 100 MHz magnetic-core inductor design with three laminations gives a 36 nH inductance, with 96.4% efficiency and an area of 3 mm^2. A comparable air-core design also gives a 36 nH inductance, with 93.45% efficiency and an area of just 2.6 mm^2. [ABSTRACT FROM AUTHOR]