Silicon-embedded toroidal inductors with magnetic cores: Design methodology and experimental validation

Abstract

An approach to the ultimate integration and miniaturization of MEMS-based 3-D magnetic components involves embedding the volume of the magnetic structures within the volume of the silicon wafer itself, exploiting microfabricated windings to create current paths, and utilizing embedded magnetic cores within the limited footprint of these components to boost the magnetic performance. However, this embedding approach imposes volumetric and microfabrication constraints that require an unusual magnetic component optimization methodology compared to wire-wound inductors and PCB inductors. These constraints dictate embedded toroidal inductors with non-overlapping windings and thin magnetic cores, and impose additional limitations on inductor design parameters such as pattern resolution, the number of winding turns and winding thickness; these constraints complicate the trade-offs to be made in designing core-integrated inductors. A design methodology encompassing these constraints is therefore needed. For a targeted inductance value within a given footprint, our design methodology addresses an inductor with a maximized quality factor based on the trade-offs between copper loss and core loss. To illustrate this methodology, siliconembedded inductors with iron powder cores are designed and fabricated; a quality factor of 24 is achieved at 30 MHz.

Soft ferrite cores characterization for integrated micro-inductors

“…For integrated ferrite-based microinductors, some authors have sintered the bottom ferrite layer for spiral-type inductors then completed it with a composite top layer [8], some have sintered the bottom and top ferrite layer in-situ [25]. Others have developed hybrid solutions where the core is fabricated off-chip [15].…”

“…A lot of research has been carried out to achieve inductor integration on-chip or in-package. Some demonstrators of air-core inductors, such as thin film magnetic inductors and ferrite based ones, have shown that each integration method has its own merits and difficulties [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. For on-chip integration, approaches to the fabrication of micro-inductors involving vacuum deposition and electrodeposition of magnetic cores have been demonstrated over the last thirty years.…”