Design, modeling, analysis, and characterization of 3-D inductors for PwrSoC/PwrSiP DC-DC converters

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Shetty, Chandra
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University College Cork
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Inductors are essential components in power supplies. Increasingly, point-of-load (POL) power delivery is now the primary issue across all market sections, such as battery-powered portable electronic systems, including laptops, smartphones, tablets, etc. With increasing performance and decreasing footprint, there is a rising demand for on-chip three-dimensional (3-D) inductors. Micro inductors are used in on-chip voltage regulators, radio-frequency (RF) circuits, microsensors, microactuators, power MEMS devices, etc. The benefits of 3-D inductors such as high inductance density can be extended to such applications. This work deals with the design, modeling, and characterization of 3-D inductors for power supply applications: Power Supply in Package (PwrSiP) and Power Supply on Chip (PwrSoC) applications. Even though much work has been carried out to fabricate high inductance density 3D inductors on silicon for power applications, little or no attention has been given to (1) develop a closed-form expression for the inductance, (2) introduce novel structures for the improved figures-of-merit, and (3) dc ratio of inductance to resistance Ldc/Rdc (also known as dc quality factor Qdc). The contributions of this thesis are as follows: (1) analytical models for the inductances of 3-D inductors (toroid, solenoid, and spiral) with air-core are developed and validated by fabricating 3-D inductors on PCB, (2) a detailed study of the impact of design parameters on dc ratio of inductance to resistance (Ldc/Rdc) of 3-D micro air-core inductors is carried out and demonstrated by fabricating inductors on PCB, and (3) design, modeling, and analysis for two novel inductor topologies with magnetic thin films are presented. Followed by the introductory and literature review chapters, in the third chapter, analytical expressions for the DC inductance of four types of 3-D inductors with circular cross-section pillars (CCSP) and rectangular cross-section pillars (RCSP) are derived: (1) a toroid with CCSP; (2) a toroid with RCSP; (3) a solenoid with CCSP; and (4) a solenoid with RCSP. The inductance models are validated against numerical solutions (ANSYS Maxwell and ANSYS Q3D) and measurement results of this work as well as previously published works. The fourth chapter of the thesis focuses on the impact of design parameters such as the number of turns, pitch, height, conductor dimensions, etc. on the Qdc of different 3-D micro air-core inductor configurations. Two well-known traditional inductors are considered for the illustration: the toroid and the solenoid. Solenoid and toroid inductors are fabricated on PCB in 5 mm X 5 mm area to validate the results from Finite Element Analysis (FEA) solutions. Subsequent two chapters explore the design, inductance modeling, and analysis of two novel magnetic core inductor topologies: the fifth chapter presents a novel 3-D spiral inductor structure with magnetic thin films and the sixth chapter introduces a novel inductor structure with a coaxial cross-section of copper conductor and a single layer magnetic thin film core surrounding it. Small-signal performance of the proposed inductors compared with the previously published works to demonstrate their potential for power supply applications; the proposed inductors have the potential to achieve higher figures-of-merit (FOM). A closed-form analytical expression for the inductance, including both air-core (winding) and magnetic core (thin-films) contributions, of the novel inductor structures is derived. Finally, the seventh chapter summarises the research findings. The experimental work in this thesis focused on PCB and silicon inductors. In general, the design, analysis, and characterization methods adapted in the thesis are valid for PCB, in-silicon, and on-silicon inductors.
3D inductor , Power supply
Shetty, C. 2023. Design, modeling, analysis, and characterization of 3-D inductors for PwrSoC/PwrSiP DC-DC converters. PhD Thesis, University College Cork.