Paul McCloskey

PCB integrated inductors for low power DC/DC converter

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 /spl times/ 10 mm/sup 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 /spl mu/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 /spl times/ 10 mm/sup 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.

Electrical performance of microtransformers for DC-DC converter applications

This paper presents the electrical performances of the fabricated microtransformers. Measurements for open-circuit and short-circuit impedance up to a frequency of 100 MHz are presented. The measured results are compared with predictions obtained from models based on an analytical approach. The use of a microtransformer in a 2-MHz dc-dc converter is reported. An efficiency of 40% for a power density of 1.2 W/cm/sup 2/ was measured.

Thick photoresist development for the fabrication of high aspect ratio magnetic coils

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.

Parasitic inductance effect on switching losses for a high frequency Dc-Dc converter

This work examines the impact of packaging parasitics on the efficiency of a synchronous DC-DC buck converter. An analytical model of the losses in the converter is developed and this is compared to practical results at switching frequencies in the range of 1-2 MHz. The effect that the packaging parasitic inductance has on efficiency is highlighted by predicting the expected losses from a converter with optimised packaging parasitics.

Thin film micro-transformers for future power conversion

This paper presents an investigation into the use of micro-fabricated transformers for future power conversion in the 5-10 MHz frequency range. The structure of the micro-transformers is described and an analytical model is used to optimize the transformer for maximum efficiency. The optimized devices are based on improved fabrication processes which give 80 /spl mu/m thick copper conductors and a two layer laminated magnetic core. The optimization suggests that an efficiency of 82% at an output power of 3.5 W can be achieved. Initial small signal results are presented for micro-transformers fabricated using the improved processes. The estimated efficiency of the fabricated microtransformer based on these results is 78%.

Thin Film Microtransformer Integrated on Silicon for Signal Isolation

Microtransformers have been fabricated on silicon substrates with the aim of providing isolation for signal and power. Interleaved primary and secondary windings are sandwiched between two electroplated magnetic layers. The transformer has a turn ratio of 4:4. It has a primary inductance of 400 nH at low frequencies and dc resistance of 0.48 Omega. The voltage gain is -1 dB between 1-20 MHz with a 50-Omega load. When compared to previously reported microtransformer characteristics this is the highest reported voltage gain for a microtransformer

Design study for ultra-flat, PCB integrated inductors for low power conversion applications

In this paper the effectiveness of integrated cores is investigated as a function of various core parameters. This is a step towards optimised magnetic structures for this novel type of component.

Design study and fabrication techniques for high power density microtransformers

This paper presents an investigation into the power density and efficiency achievable from microtransformers suitable for integration on silicon. Results from the design study indicate that high aspect ratio conductors and laminated cores are required to achieve high power density. Fabrication techniques, using thick photoresist, which can be used to achieve high aspect ratios, have been developed and results are presented. Initial test results for the inductance and resistance of the coils are also presented.

MCM-L integrated transformers for low power applications

Designs for planar magnetic core structures fabricated in printed circuit board (PCB) technology have been developed by the authors. The technology is applied to producing integrated transformers for low power conversion in this paper. It involves using processes and materials which are compatible with existing PCB techniques, and structures are designed to be integrated with other circuitry in a typical PCB layer count. Structures are designed to support voltage levels of up to 18 V at 3 W power.

Electrochemical process for the lamination of magnetic cores in thin-film magnetic components

The lamination of the core in thin film magnetic components is necessary to reduce the eddy current losses of the structure at high frequencies. The usual way to achieve lamination of the core is by physical vapor deposition (PVD) techniques. These methods are however costly and the deposition of layers is non selective. In this article, an almost entirely aqueous-based electrochemical process for the lamination of magnetic cores is presented. The process uses an electrodepositable photoresist Eagle 2100 ED codeposited with a catalyst (palladium). The Eagle layer is left as an insulator and the catalyst allows the activation of the layer for subsequent metallization. The process can be reproduced as many times as required for producing the multilayers. It is also selective: it does not require multiple photolithography steps. As a demonstration of the multilayer process, a core constituted of two layers of Ni/sub 80/Fe/sub 20/ (6 /spl mu/m each layer), separated by an Eagle insulating layer, electroplated over three-dimensional structures, was produced.