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Thin-film Si-integrated inductors with closed cores have different magnetic field distributions in the winding window space compared to the inductors with unclosed cores. One-dimensional methods are no longer applicable for these inductors to calculate the ac resistance. Based on the analysis of the magnetic field distribution of the devices, a 2-D field solution was developed, which leads to an improved 2-D method to calculate the ac resistance of the device. High accuracy of this new approach has been verified by finite-element analysis, while 1-D methods can lead to significant errors. [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]

Abstract: Micro-inductors, with an electrodeposited nickel–iron core have been fabricated on silicon substrates, and have been characterized in the frequency range up to 100MHz. The core consists of a nickel iron, 45:55 alloy which is deposited using pulse-reverse electroplating in the presence of a magnetic field to control anisotropy. The operation of the inductors with low loss at high-frequency critically depends on core thickness, which is used to control eddy-current loss as the frequency is increased. However, it is shown that the permeability of NiFe 45/55 has a dependency on thickness, and decreases with increasing thickness. For example, the permeability is measured to be approximately 1000 for a 1-μm-thick film, decreasing to approximately 400 for a 5-μm-thick film. In order to correctly design micro-inductors for operation up to 100MHz, it is important that this characteristic of the material is taken into account. [Copyright &y& Elsevier]