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Title: Design and Demonstration of Embedded Inductors for High-Voltage Integrated Voltage Regulators
Committee:
Dr. Madhavan Swaminathan, ECE, Chair , Advisor
Dr. Arijit Raychowdhury, ECE
Dr. Saibal Mukhopadhyay, ECE
Dr. Kaladhar Radhakrishnan, Intel
Dr. Mark Losego, MSE
Abstract: Increased functionalities and computational capacity of today’s electronic systems have resulted in the need for higher power density. Current multi-stage 48 V to 1 V power delivery networks shows efficiencies of 75% or lower. Substrate-embedded inductors can enable the miniaturization of power modules and Integrated Voltage Regulators (IVRs) making possible single-stage down-conversion of 12 V to 1 V or 48 V to 1 V, improving both the system efficiency and regulation bandwidth. The design rules of inductor for single-stage high-conversion-ratio IVRs are quite different and challenging compared to low voltage converter like 1.7 V to 1 V. With extensive design exploration and experimentation, we have validated a novel inductor and fabrication technology along with a novel design methodology. We have demonstrated over 42 fabricated embedded inductors with 7 different designs and 6 different magnetic materials spanning an inductance range from 10 nH to over 500 nH, DC resistance from 14 mOhm to 40 mOhm, and saturation current from 100 mA to over 5 A. We have proposed and validated a new inductor power loss calculation method that includes the effect of frequency, duty cycle, and large-signal (or hysteresis) losses, and only circuit quantities such as inductance and resistance, current ripple, and power loss need to be measured. This new method evolves in an inductor design framework that allows predicting the performance of complex embedded inductors using a discrete toroidal inductor that takes only one day to fabricate. We have demonstrated an inductor with 60 nH at 10 MHz, density of 12 nH/mm2, 23 mOhm of DC resistance, a maximum current of 5A, a current density of 1 A/mm2, and an inductance to DC resistance ratio of 2850 nH/mOhm. However, for 12 V to 1 V single-stage IVRs, more advances need to be made for the magnetic materials. We have determined that the required magnetic material needs a relative permeability of 65, loss tangent less than 0.015, saturation field over 6 kA/m, and large to small signal losses ratio of 4. Finally, a scalable small-signal SPICE model is presented. This model allows obtaining an ultra-wide-bandwidth inductor circuit representation with any amount of inductance (for a given magnetic material) using a single model to measurement fitting.
