Additively Fabricated Laminated Inductors For Miniaturized Switching Power Converters

This thesis work proposed an innovative idea to solve the problem of building a small integrated inductor, a bottleneck of realizing power supply-on chip (PwrSoC): utilization of material that has intermediate electrical conductivity as an interlamination material for a magnetic core We theoretically analyzed that the electrical conductivity of 0.1 S/m - 1 S/m is a desirable range for an interlamination material that enables sequential electrodeposition (CMOS-compatible process) yet suppression of eddy-current loss. Polypyrrole (PPy) was selected as such interlamination material to validate our idea. We empirically demonstrated sequential stacking of PPy and metallic magnetic alloy, NiFe via continuous and additive electrodeposition process. We also experimentally showed that PPy interlamination effectively suppresses eddy-current loss by building and testing inductors. A laminated 10-layer NiFe inductor showed higher inductance retention (88% vs. 21%), and lower AC resistance (1.68 ohm vs. 12.7 ohm) at 8 MHz compared to a single layer NiFe inductor having comparable total NiFe thickness; both higher inductance retention and lower AC resistance are signs of suppressed eddy current loss. We then investigated the practicality of our findings. A thick core having 45 NiFe layers was fabricated to show the developed technology can achieve tens of microns in thickness which is necessary for watt scale power converters. The air gap was introduced to increase saturation current up to 500 mA which was then implemented in a buck converter. Our toroid inductor and commercial inductor showed comparable power efficiency of ~75% in a buck converter that steps down 2.7V to 1.2 V at 20 MHz switching frequency. Although our inductor was larger than the commercial inductors, utilization of higher saturation flux density material like CoNiFe and optimization of inductor design expects to reduce inductor size.