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This paper reports the fabrication of coils for micro-magnetic devices on silicon using thick photoresists commonly used in the manufacture of microelectromechanical systems. A comparison of three photoresists, EPON SU-8, AZ 4562 and AZ 9260, is presented for the fabrication of high aspect ratio conductors. With a thickness of 81 μm, aspect ratios of 6:1 are obtained using the AZ 9260 photoresist. RF inductors and micro-transformers for power conversion applications are fabricated using this technology. The quality factor of the RF inductors shows maximum values of 23 at 0.4 GHz. Very good measurement is also obtained with the micro-transformers: the resistance of the electroplated copper windings is 0.3 Ω up to 2 MHz.

Inductor-on-silicon research to date has focused on optimising technologies for maximum power density and efficiency, with most design procedures based on computationally intensive methods. In this paper a simple and intuitive method for designing microinductors based on a given DC-DC converter specification, which includes accurate models for all loss components, is presented. A detailed examination of variations in designs to realise the same circuit performance is presented. Finally Finite Element Analysis simulations demonstrating the accuracy of the models are given, along with measured results. INDEXTERMS-DC-DC, Design, Inductor-on-silicon, Microinductor, PwrSoC 0885-8993 (c)

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Abstract-This paper discusses the use of printed circuit board (PCB) integrated inductors for low power dc/dc buck converters. Coreless, magnetic plates and closed core structures are compared in terms of achievable inductance, power handling and efficiency in a footprint of 10 10 mm 2 . The magnetic layers consist of electroplated NiFe, so that the process is fully compatible with standard PCB process. Analytic and finite element method (FEM) methods are applied to predict inductor performance for typical current waveforms encountered in a buck converter. Conventional magnetic design procedures are applied to define optimum winding and core structures for typical inductor specifications. A 4.7 H PCB integrated inductor with dc current handling of up to 500 mA is presented. This inductor is employed in a 1.5 W buck converter using a commercial control integrated circuit (IC). The footprint of the entire converter measures 10 10 mm 2 and is built on top of the integrated inductor to demonstrate the concept of integrated passives in power electronic circuits to achieve ultra flat and compact converter solutions.

This paper presents a review and summary of the PSMA "PSiP2PwrSoC" special project that investigated the technology and performance underpinning recent commercial developments in Power Supply in Package and Power Supply on Chip. The results of this study are based on the identification of more than 28 commercial products, six of which were analyzed in detail, both physically and electrically. The methodology of the project is described and some of the salient results of this benchmarking effort are presented. In this study, a representative subset of the available commercial products was selected and a comprehensive physical, electrical and thermal performance analysis was carried out. The objectives were to identify the components, materials and assembly technologies used, and to determine if the drive toward greater integration and higher power density affected the performance of newer devices. The results of the analysis were then used to determine the current state of the technology in this application space, to show how it has developed to date and to predict how it might progress in the future. These results are presented in a generic format that does not identify individual products. This project was co-sponsored by the PSMA and member companies. The final report of the project, which includes more detailed information on the reviews described here as well as considerable trending analysis, is now available.Index Terms-Power supply in package (PSiP), power supply on chip (PwrSoC).

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