Integrated transformer with laminated magnetic core [electronic resource]

Integrated transformers and inductors are critical and widely used passive components in many circuits such as power converters, voltage regulators, and radio-frequency (RF) circuits. The area of power supply management has an interesting opportunity for integrated magnetic components, where comparatively large inductances are required at frequencies in the low-megahertz range. These values would be difficult to achieve using the widely used planar spiral inductors. The first part of this thesis reviews the design and fabrication of magnetic integrated transformers with compact area and high performance. The design uses two equivalent magnetic cores in interleaved solenoid coils to minimize chip area usage, with a 1:1 turns ratio. In a coupled inductor topology, the high coupling can also be used to decrease the magnetic flux within the magnetic core, mitigating saturation effects. The coupling coefficient is one of the most important measures of transformer efficiency as it presents the most direct and consistent gauge for of energy loss. This thesis demonstrates magnetic-core transformers with greater than 97% coupling between primary and secondary coils with a (primary or secondary) inductance of 565 nH. This inductance represents an enhancement of more than 60 times that of air core inductors of identical geometry. Without the addition of the core, there is almost no magnetic coupling between the two solenoids. By using the laminated magnetic core structure, the quality factor of the primary (or secondary) inductance was increased to a peak value of 6.3 with 3 [micrometers] thick electroplated copper coils. The combined effect of the very high coupling and respectable quality factor results in a high total transformer efficiency, measuring at 80% (-1.1 dB). This efficiency is very competitive with other transformers in the literature, however the device uses significantly thinner copper layers than the other highly performing devices. The thinner copper layers play an important role in the overall manufacturability and reliability of the device. If the copper thickness could be increased to comparable thickness with other research devices, the transformer would deliver even more impressive quality factor and efficiency. In the second part of this thesis, I analyze the presence of multiple resonance peaks observed in the permeability spectrum of sputtered magnetic thin films. These resonance peaks in the permeability spectrum translate into additional nonlinearities and losses for inductor and transformer devices that do not control for the peaks during the film deposition. In this work, in-plane magnetized films of CoTaZr demonstrate standing spin wave resonances in the complex permeability spectra well below the ferromagnetic resonance frequency. From detailed analysis of the static field dependence of the modes combined with observation of the magnetic domains using Kerr effect microscopy, it is proposed that these modes originate from spin waves within the Bloch walls where the magnetization rotates perpendicular to the plane of the film. Unlike spin waves typically described in perpendicularly magnetized films, the frequencies involved are much lower due to field dynamics inside the wall. This theory can be fully understood by incorporating these observations into an analytical model using the Landau-Lifshitz-Gilbert equation, with good agreement between model and experimental measurement.

Keywords: Electrical Engineering.
Advisor: Wang Shan primary advisor. Thesis advisor
Poon Ada Shuk Yan
White Robert M.