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EETE DECEMBER 2012

NEWS & TECHNOLOGY Solar energy funnel offers new way of harnessing photons for electricity By Paul Buckley MIT engIneers have ProPosed a new way of harnessing visible light, but also some of the invisible spectrum, which ac- photons for electricity with a ‘solar energy funnel’ that has the counts for much of sunlight’s energy. potential for capturing a wider spectrum of solar energy. “We’re Xiaofeng Qian, a postdoc in MIT’s department of nuclear trying to use elastic strains to produce unprecedented material science and engineering who was a co-author of the paper, properties,” said Ju Li, an MIT professor and corresponding au- explains that elastic strain corresponds to stretched atomic thor of a paper describing a new solar-funnel concept published bonds, while an inelastic, or plastic strain corresponds to in the journal nature Photonics. broken or switched atomic bonds. a spring that In this case, the ‘funnel’ is a metaphor: elec- is stretched and released is an example of elastic trons and their counterparts, holes — which are strain, whereas a piece of crumpled tinfoil is a split off from atoms by the energy of photons case of plastic strain. The new solar-funnel work — are driven to the center of the structure by uses precisely controlled elastic strain to govern electronic forces, not by gravity as in a house- electrons’ potential in the material. The MIT team hold funnel. and yet, as it happens, the material used computer modelling to determine the effects actually does assume the shape of a funnel: It of the strain on a thin layer of molybdenum disul- is a stretched sheet of vanishingly thin material, fide (MoS2), a material that can form a film just a poked down at its center by a microscopic needle single molecule (about six angstroms) thick. that indents the surface and produces a curved, The elastic strain, and therefore the change funnel-like shape. that is induced in electrons’ potential energy, changes with their The pressure exerted by the needle imparts elastic strain, distance from the funnel’s center, much like the electron in a which increases toward the sheet’s center. The varying strain hydrogen atom, except this “artificial atom” is much larger in changes the atomic structure just enough to “tune” different size and is two-dimensional. In the future, the researchers hope sections to different wavelengths of light — including not just to carry out laboratory experiments to confirm the effect. CMOS-compatible wafer-level 2D thin-film magnetic cores By Julien happich enPIrIon has Begun the commercialization of a new mag- “Increasing the switching frequency allows the use of smaller netic alloy which enables the miniaturization of passive mag- inductors utilizing electroplated WLM materials that can be netic components and their assimilation with integrated circuits post-CMos processed. We developed an amorphous Fe- at wafer level. Co based alloy called FCa, which is capable of operating at So-called wafer level magnetics (WLM) frequencies higher than 20MHz with minimal present a leap in traditional technology, says attenuation of magnetic properties,” explains the company, taking magnetic components dr. Trifon Liakopoulos, director of MeMs from their 3-dimensional discrete shape to a technology and enpirion’s co-founder. “With planar 2-dimensional thin-film form that can be wafer electroplating methods, it is possible to deposited with standard wafer processes on cost-effectively deposit photo-lithographically top of CMos wafers. enpirion’s WLM technol- defined FCA magnetic cores on silicon wafers.” ogy is fully qualified for full-scale mass produc- FCa has high resistivity, low coercivity and tion in a high volume foundry and enables the maintains high effective permeability at fre- industry’s first ever Power System-on-Chips quencies higher than 20MHz. FCA’s high mag- based on electroplated wafer level magnetics. developed with a netic saturation makes it suitable for use as single or multiple view to achieving monolithic Power system-on-Chips, the WLM layers in power circuits, where it is compatible with flip-chip, technology can be easily transferred to other micro-magnetic wire-bonding and solder re-flow packaging methods. applications, for example micro-transformers for signal isola- enpirion developed a turnkey process module, which fea- tion, micro-electromagnets for life sciences, integrated mag- tures low cost of ownership plating equipment to deposit FCa netic sensors for navigation and PMICs for portable consumer on 6 inch or 8 inch wafers. The technology has been success- applications. fully transferred and embedded in a volume wafer production facility earlier this year. 16 Electronic Engineering Times Europe December 2012 www.electronics-eetimes.com


EETE DECEMBER 2012
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