Microfabrication of air core power inductors with metal-encapsulated polymer vias

Abstract

This paper reports three-dimensional (3-D) microfabricated toroidal inductors intended for power electronics applications. A key fabrication advance is the exploitation of thick metal encapsulation of polymer pillars to form a vertical via interconnections. The radial conductors of the toroidal inductor are formed by conventional plating-through-mold techniques, while the vertical windings (up to 650 µm in height) are formed by polymer cores with metal plated on their external surfaces. This encapsulated polymer approach not only significantly reduces the required plating time but also exploits the relative ease of fabricating high-aspect-ratio SU-8 pillars. To form the top radial conductors, non-photopatternable SU-8 is introduced as a thick sacrificial layer. Two toroidal inductor geometries were fabricated and tested. The first inductor had an inner diameter of 2 mm, an outer diameter of 6 mm, 25 turns and a vertical via height of 650 µm. The second inductor had an inner diameter of 4 mm, an outer diameter of 8 mm, 50 turns and a vertical via height of 650 µm. Both inductor geometries were successfully fabricated and characterized in the frequency range of 0.1−100 MHz. Characterization results of the 25-and 50-turn inductors showed an average inductance of 76 and 200 nH, a low frequency (0.1 MHz) resistance of 0.2 and 1 and a quality factor of 35 and 24 at 100 MHz, respectively. Finite-element simulations of the inductors were performed and agreed with the measured results to within 8%. The turn-to-turn breakdown voltage was measured to be in excess of 800 V and currents as high as 0.5 A could be successfully carried by the inductor windings.

A MEMS-based Double-layer Spiral Planar Inductor using Patterned Permalloy filled with Ferrite/Polyimide Composite Materials as Magnetic Layers

“…; (c-d) Magn are PI insula piral plane te materials sor. The fer sure the ferr ed and solid windings wa ist was spin ing [9]. The uble-layer sp ized by a th electroplat between th cated by so netic flux ation, while e using the s insulation, rrite powder rite powder dified on the as prepared n coated on en the spiral piral planar hrough-hole ted after the he two coil me MEMS e , r, r e d n l r e e l S…”

A Technology Overview of the PowerChip Development Program

“…The first approach, which emphasizes system compactness, embeds inductors within the volume of a silicon wafer, and uses highpower through-wafer interconnects [74], similar to the way a back-side spiral inductor was embedded and connected in [39]. The second approach, which maximizes the quality factor on loss-less substrates, uses metal-encapsulated polymer vias to realize high-aspect-ratio vertical conductors [75]. The sample 6-mm-diameter copper-electroplated inductors had 25 turns with heights ranging from 300 to 650 μm.…”

Fabrication of 3D air-core MEMS inductors for very-high-frequency power conversions

“…One method to fabricate on-substrate high-aspect-ratio 3D inductors is to use UV-LIGA lithography with SU-8 negative resist. The resist structures serve as electroplating molds and sacrificial layer [19][20][21] or supporting pillars 22,23 for the electrodeposition of conducting metals. The second category is embedded inductors, in which the inductors are embedded inside the Si substrate and utilize the unused substrate volume.…”