A toroidal power inductor using radial-anisotropy thin-film magnetic material based on a hybrid fabrication process

Abstract

This paper presents improvements for the design and fabrication of high-frequency toroidal power inductors with and without radial-anisotropy thin-film magnetic material. An improved winding resistance model for toroids is developed considering an angle factor for actual winding shape, the effect of spacing between turns and loss associated with exterior current in the circumferential direction. A hybrid process for fabricating low-profile magnetic-core toroids is presented. The process uses standard flex printed circuit board (PCB) technology for the top and bottom winding layers with vias electroplated after sandwiching the magnetic core between the two winding layers. Thin-film magnetic material (Co-Zr-O) is deposited in the presence of a radial magnetic field, which induces radial anisotropy in the toroidal core. Small-signal measurements show that the toroidal core has a relative permeability over 40 at frequencies up to several hundred megahertz, and very high quality factor in the frequency range below 100 MHz. Aircore and magnetic-core toroidal inductors using this hybrid fabrication process were built and tested at small-signal levels. Magnetic-core toroids showed a higher inductance and quality factor than air-core toroids at frequencies below 100 MHz. This winding loss model and fabrication process can be applied to both air-core and magnetic-core toroidal inductors.

Complex permeability measurements of radial-anisotropy thin-film magnetic toroidal cores

“…Detailed and accurate winding loss analysis are provided in [12], [13]. A winding configuration for reducing external flux, and capacitance is discussed in [14].…”

“…A winding configuration for reducing external flux, and capacitance is discussed in [14]. Coil fabrication technologies in a printed circuit board or with wafer-level integration have been developed in [13], [15]- [20]. Methods for developing radially anisotropic toroidal cores have been presented in [9], [10].…”

Analytical model of a resonator for PCB-embedded power conversion

“…Embedding power converters into printed circuit board (PCB) substrates can be an efficient way to increase power density, improve modularity and reliability, simplify cooling, and decrease manufacturing costs [1,2]. In particular, various structures with PCB-based magnetic components have been studied such as 2D windings and 3D cores (e.g., racetrack, pot core) [3,4,5], 3D windings and 2D cores (e.g., toroid, meander) [6,7,8], or air-core components [9,10,11].…”

Study of a Topology of Low-Loss Magnetic Component for PCB-Embedding

“…Many research papers have dealt with integrated and planar magnetic components, including coils, transformers and resonant circuits. These publications focused on manufacturing techniques [1,2,3,4], modelling [1,5], optimization [3], and simulation [1,6,7,8].…”

“…Various structures have been studied, planar [2,9], with solenoid-like structures (windings surrounding the magnetic corelike a toroid inductor) [1,4,10], with pot-core-like structures (core surrounding the windingslike with a PQcore) [3] or air-core components [6,7,8].…”