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Laminated metallic alloy cores (i.e., alternating layers of thin film metallic alloy and insulating material) of appropriate lamination thickness enable suppression of eddy current losses at high frequencies. Magnetic cores comprised of many such laminations yield substantial overall magnetic volume, thereby enabling high-power operation. Previously, we reported nanolaminated permalloy (Ni80Fe20) cores based on a sequential electrodeposition technique, demonstrating negligible eddy current losses at peak flux densities up to 0.5 T and operating at megahertz frequencies. This paper demonstrates improved performance of nanolaminated cores comprising tens to hundreds of layers of 300–500-nm-thick CoNiFe films that exhibit superior magnetic properties (e.g., higher saturation flux density and lower coercivity) than permalloy. Nanolaminated CoNiFe cores can be operated up to a peak flux density of 0.9 T, demonstrating improved power handling capacity and exhibiting 30% reduced volumetric core loss, attributed to lowered hysteresis losses compared to the nanolaminated permalloy core of the same geometry. Operating these cores in a buck dc–dc power converter at a switching frequency of 1 MHz, the nanolaminated CoNiFe cores achieved a conversion efficiency exceeding 90% at output power levels up to 7 W, compared to an achieved permalloy core conversion efficiency below 86% at 6 W.

We present fabrication, electrical characterization, and performance reliability of electrodeposited, nanolaminated soft magnetic metallic cores with dip-coated flouroacrylic polymer interlamination insulations. The nanolaminated cores are comprised of hundreds of submicron-thick CoNiFe layers that are electrically-insulated from the neighboring layers by ~100 nm-thick fluoroacrylic polymer layers. A fluoropolymer coating solution is utilized to achieve electrical insulation between the individual magnetic layers while the layers are being assembled into a single core. Superior magnetic energy densities, surpassing that of conventional ferrite materials, are achieved even at high operating frequencies up to 10 MHz while the eddy current losses within the individual magnetic layers are suppressed. For the ultimate miniaturization of an inductor, the microfabrication of coil is achieved "on" the surface of the core. Reliability tests, i.e., temperature cycling test and corrosion test, are performed to study potential performance degradation of the nanolaminated cores in actual operation environments.

We report an approach to achieve composite materials with wide-ranging macroscale mechanical properties through the three-dimensional structural manipulation of low-dimensional subcomponents. Such composites could be useful in MEMS actuators based on highly compliant mechanisms, or in mechanical metamaterials with highly anisotropic mechanical properties (e.g., negative Poisson ratio). The presented composites possess a multilayer structure comprising alternating high modulus and low modulus subcomponent materials (i.e., permalloy (Ni 80 Fe 20 ) and polydimethylsiloxane (PDMS) elastomer), within which lithographically-patterned pores are present. By controlling the pore geometries/orientations and the individual metal/elastomer layer thicknesses in the microscale, in-plane and out-of-plane mechanical properties (i.e., tensile and bending moduli) are substantially tailored.

Metallic magnetic materials have desirable magnetic properties, including high permeability, and high saturation flux density, when compared with their ferrite counterparts. However, eddy-current losses preclude their use in many switching converter applications, due to the challenge of simultaneously achieving sufficiently thin laminations such that eddy currents are suppressed (e.g., 500 nm-1 μm for megahertz frequencies), while simultaneously achieving overall core thicknesses such that substantial power can be handled. A CMOS-compatible fabrication process based on robot-assisted sequential electrodeposition followed by selective chemical etching has been developed for the realization of a core of substantial overall thickness (tens to hundreds of micrometers) comprised of multiple, stacked permalloy (Ni80Fe20) nanolaminations. Tests of toroidal inductors with nanolaminated cores showed negligible eddy-current loss relative to total core loss even at a peak flux density of 0.5 T in the megahertz frequency range. To illustrate the use of these cores, a buck power converter topology is implemented with switching frequencies of 1-2 MHz. Power conversion efficiency greater than 85% with peak operating flux density of 0.3-0.5 T in the core and converter output power level exceeding 5 W was achieved.

Selective, template-assisted growth of electrodeposited, layered materials leads to the top-down designable realization of nanopatterned surfaces with a large surface area (>1 cm(2)) comprised of multi-dimensional, multiscale (10 nm-1 μm) features, without the need of standard nanolithography. This process opens a manufacturable route to functional nanodevices that rely on anisotropic, nanoscale surface structures with controlled dimensions.

Many magnetic MEMS devices such as magnetic-based microscale energy harvesters rely on the availability of microscale permanent magnets capable of generating significant magnetic fluxes. Ideally, these magnets would be able to be integrated with MEMS in a batch-fabrication-compatible manner. A number of thin film permanent magnets possessing excellent intrinsic magnetic properties have been discussed in the literature. In order to achieve higher extrinsic properties such as magnetic flux, an intuitive approach is to simply increase the magnetic film thickness. However, it is observed that as the magnetic film thickness increases, the intrinsic magnetic properties (such as remanence and maximum energy product) often deteriorate, limiting the maximum achievable magnetic fluxes from these small-scale integrated magnets. In this work, we present a microfabricated permanent magnet with a multilayer structure that preserves the high magnetic energy density (and resultant magnetic flux density) of thinner magnetic films while simultaneously achieving a significant magnetic thickness and resultant extrinsic properties. The fabrication process relies on sequential multilayer electroplating: alternating layers of relatively thin (in microns) magnetic films and non-magnetic materials were electrodeposited in a multilayer fashion realizing a laminated permanent micromagnet up to a total magnetic thickness of 80µm. A maximum energy product as high as 16.2kJ/m 3 (~ 70% of the value of a 1-µm-thick thin film) was retained in the laminated permanent micromagnet, and a 30% improvement over a CoNiP nonlaminated film with the same magnetic thickness has been successfully achieved. This fabrication approach could potentially be adapted to other permanent magnet materials systems.

This study reports the fabrication and characterization of a metal-oxide-based supercapacitor with a high surface area 3D microelectrode. This microelectrode is comprised of high aspect ratio SU-8 pillars that are fabricated using backside exposure and coated with alternating Ni and Cu layers via a sequential electrodeposition process. High surface area Ni electrodes are obtained by selective removal of the Cu sacrificial interlayers. Through subsequent electrochemical deposition and heat treatment techniques, these electrodes are conformally coated with nickel oxide. Performance tests are carried out via cyclic voltammetry. Devices were cycled in excess of 400 times with insignificant capacitance degradation. The estimated areal capacitance is found to be 270 mF/cm2 which is among the highest areal capacitance values reported for MEMS supercapacitors.

This paper presents batch microfabrication and experimental characterization of solenoid inductors with electrodeposited silver windings and laminated core. To enable high-frequency operation, the metallic magnetic core consists of multiple air-insulated, electroplated micron-thick permalloy (Ni80Fe20) laminations, with total core thicknesses up to tens of microns. The core is achieved by sequential electrodeposition of permalloy and copper, followed by selective removal of the copper, thereby releasing the core laminations. Electroplated silver is selected as winding material for its low resistivity and to withstand the copper etching required during core release. Release of the core laminations is the final inductor fabrication step, reducing potential process-induced damage to the core. Two inductors sharing one laminated core in a transformer geometry are fabricated, and exhibit inductances of approximately 100 nH at 5 MHz, resulting in an inductance density of 29 nH/mm2. This process demonstrates processing compatibility of using silver windings with highly-laminated, fully-integrated magnetics.

This paper presents a polymer hollow microneedle array for transdermal drug delivery that is fabricated using UV photolithography and a single-step micromolding technique. This fabrication process patterns a 6×6 array of 1mm tall high-aspect-ratio hollow microneedles with sharp beveled tips and 150µm diameter side-opened lumens. The geometry of the beveled tip and the position of the lumen are defined simultaneously by a two-dimensional lithography mask pattern and the topography of the micromold. This three-dimensional geometry improves insertion performance and potentially the drug delivery efficiency without additional fabrication processes. These hypodermic-needle-like microneedles have been successfully constructed, packaged, and tested for fluidic functionality and skin penetrability.

This paper presents a fabrication process combining micromolding and direct drawing, and its application to the development of high aspect ratio microneedles. Without using photolithography or etching, the proposed process creates microneedles with: 1) higher aspect ratios than that of the original mold, 2) controllable needle diameter for optimized mechanical strength, and 3) arrowhead-shaped tips for potentially increased capacity and effective payload delivery. The needles presented are formed with biocompatible, water-soluble polymers, but the fabrication process inherently allows many kinds of polymers to be exploited. Various high aspect ratio 3D structures were fabricated and characterized, and the fabrication result was compared with theoretical prediction. Water-soluble microneedle arrays have been fabricated and successfully penetrated into porcine skin, fully releasing the drug-surrogate into the dermis layer within a minute.

This paper presents a rectangular, anisotropic nanolaminated CoNiFe core that possesses a magnetically hard axis in the long geometric axis direction. Previously, we have developed nanolaminated cores comprising tens to hundreds of layers of 300–1000 nm thick metallic alloys (i.e. Ni80Fe20 or Co44Ni37Fe19) based on sequential electrodeposition, demonstrating suppressed eddy-current losses at MHz frequencies. In this work, magnetic anisotropy was induced to the nanolaminated CoNiFe cores by applying an external magnetic field (50–100 mT) during CoNiFe film electrodeposition. The fabricated cores comprised tens to hundreds of layers of 500–1000 nm thick CoNiFe laminations that have the hard-axis magnetic property. Packaged in a 22-turn solenoid test inductor, the anisotropic core showed 10% increased effective permeability and 25% reduced core power losses at MHz operation frequency, compared to an isotropic core of the identical geometry. Operating the anisotropic nanolaminated CoNiFe core in a step-down dc–dc converter (15 V input to 5 V output) demonstrated 81% converter efficiency at a switching frequency of 1.1 MHz and output power of 6.5 W. A solenoid microinductor with microfabricated windings integrated with the anisotropic nanolaminated CoNiFe core was fabricated, demonstrating a constant inductance of 600 nH up to 10 MHz and peak quality factor exceeding 20 at 4 MHz. The performance of the microinductor with the anisotropic nanolaminated CoNiFe core is compared with other previously reported microinductors.

We report microfabricated toroidal inductors with nanolaminated ferromagnetic metallic cores for chip-scale, high-power switching converters. The fabrication process of the toroidal inductor is based on individual manufacturing of partial windings (i.e. bottom and vertical conductors) and nanolaminated magnetic core, and integrating them by means of a drop-in approach. The nanolaminated ferromagnetic metallic cores presented in this paper consist of many multilayers of electrodeposited CoNiFe films, each layer with sub-micron thickness, with a total core thickness exceeding tens of microns. The beneficial magnetic properties (i.e. high saturation flux density and low coercivity) of CoNiFe alloys are well suited for chip-scale inductors as they achieve both large energy storage capacity as well as minimized volumetric core losses at high operating frequencies due to their nanolaminated structure. A drop-in integration approach, introduced to combine the microfabricated toroidal inductor windings with the magnetic cores, allows ease of integration. An advantage of this hybrid approach over monolithic fabrication in this application is the potential use of a wide variety of core materials, both microfabricated and bulk-fabricated, and which may or may not ultimately be CMOS-compatible. Exploiting this drop-in approach, 30-turn- and 50-turn-toroidal inductors integrated with nanolaminated CoNiFe cores, having 10 mm outer diameter and 1 mm thickness, have been successfully developed. Both types of inductors exhibit inductances higher than 1 µH at frequencies up to tens of MHz, showing ten times the inductance of an air core device with the same nominal geometry. The peak quality factor of the 30-turn-toroidal inductor reaches 18 at 1 MHz.

The fabrication and characterization of highly laminated (~40 layers), thick (~40 μm) films of magnetically soft cobalt-nickel-iron are presented. Thick film fabrication is based on automated sequential electrodeposition of alternating CoNiFe and copper layers, followed by selective copper removal. The film, comprised tens of 1 μm thick laminations, exhibits saturation flux density of 1.8 T and coercivity of approximately 1.3 Oe. High-frequency film characterization took place in a 36-turn test inductor, which demonstrated constant inductance of 1.6 μH up to 10 MHz, indicating suppressed eddy-current loss. Quality factor exceeding 40 at 1 MHz, surpassing the performance of similarly fabricated Permalloy (Ni80Fe20) films.