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Inter-Wafer Inductors with Magnetic Core for 3D Power Delivery
Keywords: Power Delivery, 3D Integration, Soft Magnetic Materials
Power delivery is becoming a major issue in deep sub-micron microprocessors due to the rapid increase in power density, switching frequency and the continuous decrease of operation voltage. Increasing the input voltage, moving the power regulator closer to the microprocessor by integrating it on chip, or using on-chip inductors operating at higher frequency can alleviate the conventional power delivery problems. However, on-chip inductors pose difficulty in processing as ferromagnetic materials are generally incompatible with CMOS technology. In addition, traditional on-chip inductors are area expensive, and exhibit poor yield and performance. Three dimensional (3D) hyper-integration provides a potential solution for power delivery systems by integrating inter-wafer inductors with a magnetic core into power delivery circuitry. In a 3D power delivery architecture, a cellular array of voltage regulator modules (VRMs) on a thinned wafer is vertically integrated with the microprocessor wafer using wafer-to-wafer bonding and through silicon vias (TSVs), with the inter-wafer inductor in between. In this work, an inter-wafer inductor design with magnetic materials is investigated using 3D hyper-integration technology. The inductance and L/R ratio of inter-wafer inductors are evaluated based on the requirements of a prototype dc-dc converter. A two-leg coupled 3D inductor is designed and simulated using Maxwell 3D electromagnetic simulator to determine its quality factor and L/R ratio. The influence of the inter-wafer inductor L/R ratio on the efficiency of the dc-dc converter is analyzed. Fabrication of an inductor suitable for 3D integration with a CoFeAl based core will be presented, along with characterization results.
Mark E. Anderson, Student
Rensselaer Polytechnic Institute
Troy, NY

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