Integrated Magnetics for Future DC-DC Microprocessor Power Delivery
Author: Brice Jamieson
Publisher:
Published: 2010
Total Pages: 288
ISBN-13:
DOWNLOAD EBOOKIntegrated, switched-mode DC-DC converters are becoming widely adopted for in-package or on-chip power supply applications, however a limiting factor in their development is the relatively large size of passive components which are necessary in such a converter. By increasing the switching frequency above 100 MHz, a significant reduction in the inductance necessary for such a converter may be achieved and as a result a dramatic reduction in micro-inductor sizes may be afforded. Although considerable work has been done in the field of high-frequency micro-inductors on silicon, most of these devices have attempted to increase the inductance of such a structure at the expense of current-handling capacity, resulting in a low-power device. High-power micro-inductors, additionally, have only recently achieved a 100 Mhz operation frequency at the expense of significant losses in the thin-film magnetic enhancement layers used in these structures. If a high-power device is to successfully operate at 100 MHz with low loss, a combination of improved device design and novel magnetic thin-films is necessary. The goal of this work is to define the parameters of a high-frequency, power micro-inductor suitable for integration into an on-chip power conversion module. To achieve this goal, device and material models were developed for the first time to characterise these devices. Magnetic thin-films were characterized to ascertain the suitability of an electrodeposited thin-film as a replacement for RF-sputtered materials, desirable for the ability of an electrodeposited material to be plated in conformally thicker layers to achieve the required power density. Thin-film models were developed to extend the high-frequency permeability spectrum to account for the conductive seed layer present in an electrodeposited thin-film and the effects of shape and material thickness on anisotropy and permeability were modelled. These material models were verified against experimentally measured thin-films and determined to accurately predict the parameters of a thin-film material when it is integrated into a bounded geometry such as would be present in a micro-inductor. Device models were developed which analyze the inductance and loss in a micro-inductor structure, taking into account the shape-dependent anisotropy model and the presence of magnetic core-closure structures deposited to close the flux path between magnetic planes in a structure. The presence of gap in these core-closures is also considered which considers the cases of a non-magnetic and a magnetic gap. These models were verified against finite-element analysis as well as against fabricated micro-inductors. Finally, optimised stripline micro-inductors were fabricated and characterised for high-current and for high-frequency operation. Comparing these devices to the values expected from the device model, it is seen that the effects of shape and thickness predicted by the analytic models are seen in the fabricated structures, as well as a dependency of these on the magnitude of the AC current through the micro-inductors.
