Micromachined Thick-Film Copper Power Inductors and Transformers for Integrated Power Converters

Meyer, Christopher; Bedair, Sarah S.; Morgan, Brian; Arnold, David P.

doi:10.31438/trf.hh2010.124

Cited by 5 publications

(12 citation statements)

References 15 publications

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“…Microfabrication-based compact inductors and transformers for switching converters are therefore being increasingly studied. Typical inductor geometries include racetrack [4,5] and circular/rectangular spiral types [6][7][8][9][10]. Many reported microfabricated inductors possess planar geometries so as to exploit the use of well-developed planar microfabrication processes.…”

Section: Introductionmentioning

confidence: 99%

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

Kim

Herrault²,

Yu³

et al. 2013

J. Micromech. Microeng.

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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.

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Section: Introductionmentioning

confidence: 99%

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

Kim

Herrault²,

Yu³

et al. 2013

J. Micromech. Microeng.

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“…Plated metal processes are heavily used in MEMS power [1] and RF components [2] due to their ability to quickly and cheaply deposit thick layers for low resistances and correspondingly low power losses. For large released devices, mechanical supports are often necessary to improve robustness and to prevent deflection and shorting with neighboring structures.…”

Section: Introductionmentioning

confidence: 99%

“…For large released devices, mechanical supports are often necessary to improve robustness and to prevent deflection and shorting with neighboring structures. Since electroplated metals are conductive, creating resistive or dielectric supports has traditionally been done by the deposition and patterning of additional dielectric materials-typically polymers as in [1] and [2]. Although the ability of copper to form thick layers of oxides has been viewed as a major problem, especially in MEMS packaging where exposure to temperatures of several hundred degrees Celsius may be required [3], this property can be leveraged to completely oxidize structures larger than would be possible for other materials.…”

Section: Introductionmentioning

confidence: 99%

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Thick film oxidation of copper in an electroplated MEMS process

Lazarus¹,

Meyer²,

Bedair³

et al. 2013

J. Micromech. Microeng.

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Copper forms a porous oxide, allowing the formation of oxide layers up to tens of microns thick to be created at modest processing temperatures. In this work, the controlled oxidation of copper is employed within an all-metal electroplating process to create electrically insulating, structural posts and beams. This capability could eliminate the additional dielectric deposition and patterning steps that are often needed during the construction of sensors, waveguides, and other microfabricated devices. In this paper, copper oxidation rates for thermal and plasma-assisted growth methods are characterized. Time control of the oxide growth enables larger copper structures to remain conductive while smaller copper posts are fully oxidized. The concept is demonstrated using the controlled oxidation of a copper layer between two nickel layers to fabricate nickel inductors having both copper electrical vias and copper oxide support pillars. Nickel was utilized in this demonstration for its resistance against low temperature oxidation and interdiffusion with copper.

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“…At Hilton Head 2010 [6] we presented a process for realizing 3D air-core microinductors and transformers formed in 10-!mthick copper layers. Leveraging strong magnetic coupling between vertically stacked, tightly wound planar spirals, the devices yielded high inductance densities >100 nH/mm 2 [7].…”

Section: Introductionmentioning

confidence: 99%

Ultra-Miniaturized Power Converter Modules Using Micromachined Copper Scaffolds

Meyer¹,

Bedair²,

Morgan³

et al. 2012

2012 Solid-State, Actuators, and Microsystems Workshop Technical Digest

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This paper presents ultra-miniature (<2 mm 3 ) power converter modules with high power density (77 W/cm 3 ) enabled by micromachined 3D copper scaffolds containing high-inductancedensity (130 nH/mm 2 ) air-core power inductors. The scaffolds are formed by electroplating multiple, 30-!m-thick layers of copper within patterned photoresist molds, yielding freestanding copper traces with >10:1 aspect ratios. After backfilling with a chemically-resistant polymer, the scaffolds are then fully detached from the silicon fabrication wafer by wet-etching an underlying oxide layer. Surface-mount switch/controller chips and capacitors are attached by solder reflow to the copper scaffolds, forming selfcontained converter modules.

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Micromachined Thick-Film Copper Power Inductors and Transformers for Integrated Power Converters

Cited by 5 publications

References 15 publications

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

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

Thick film oxidation of copper in an electroplated MEMS process

Ultra-Miniaturized Power Converter Modules Using Micromachined Copper Scaffolds

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