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Going from flat to 3D A fabrication strategy mimics biological folding to produce self-assembled 3D electronic structures.
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stance, capacitors are currently built first f linear strings of amino acids can fold cause “the crimp marks provide a wellinto functional 3D protein structures, defined hinge with built-in torsional sta- and then added to the circuit board. bility” and help to guide the subsequent Any time the fabrication involves a why can’t devices do the same? George robot going in, picking up and placing folding process. He adds, “You can enWhitesides, Mila Boncheva, Derek parts, it becomes difficult if the Bruzewicz, Adam Winkleman, and (a) parts are small, he says. One way colleagues at Harvard University Cu E A Mylar 2.5 µm to circumvent the problem would and Firmenich SA (Switzerland) Crimp 5 mm Dip-coat be to have the capacitors self-ashave come up with a fabrication B with solder semble and integrate themselves method inspired by protein foldF Al within the circuit board, elimiing: Given the right set of condipresses nating the need for a robot. tions, a piece of flat tape patterned Self-assembly of electronic dewith metal will self-assemble into G vices is also of interest for flexible a functional 3D electronic struc12 mm displays and “smart” clothing, acture (J. Am. Chem. Soc. 2006, Heat, cording to Rashid Bashir of Pur128, 9314 –9315). Fold C agitate due University. He says, “The “If you look in nature, you find H + Mylar D tape 2.5 µm idea of having electronics all that there are many structures that around us, and [even] on us are made by a common synthetic (b) someday, goes towards the goal approach,” says Whitesides. The of learning more from biology approach “is to make a tape— and using biomimetic approachprotein coming off the ribosome es” more effectively. However, he or RNA coming out of the RNA says researchers in the field are polymerase—which [then] spontafaced with the challenge of obneously folds up into an ordered, taining sufficiently high yields of functional 3D structure.” integrated devices produced by The investigators developed the self-assembly. “It’s not good fabrication strategy so that it com5 mm enough, at the end of the day, to bined planar photolithography techniques with self-assembly. (a) Schematic to explain how a patterned, flat tape folds into make a few or even hundreds of devices,” explains Bashir. “You They patterned flexible Mylar tape a 3D structure. (b) Photos of a flat tape patterned with copwant more than hundreds of with metal features and dip-coatper before and after the self-assembly process. thousands of devices, and you ed the metal with solder. The patwant them all to work.” vision making a miniaturized system terned tape was then crimped into a Whitesides and colleagues are continthat has the ability to sense in all kinds quasi-3D zigzag shape. The zigzagged uing to look to nature for more inspiraof directions.” tape was attached to a second piece of tion when it comes to fabrication. “NaThe investigators demonstrated that flat Mylar tape. The investigators shook they could fabricate devices by attaching ture has been so prolific in coming up the structure in a bath heated to a temwith very interesting strategies for takperature just below the melting point of electronic elements to the uncrimped tape to produce a millimeter-sized, 360° ing soft [materials] and making functhe solder. This step caused capillary intional 3D structures,” says Whitesides. light detector. Whitesides says the most teractions between the drops of solder “One of the approaches we’re looking interesting length scale for components to drive the tape to fold into a more at, for example, is [how] to make a jelly is ~100 µm. “I think that will give the complex 3D structure. roll. You take a sheet and you roll it up best compromise between practicality, Heiko Jacobs, a former Whitesides into a coiled structure. That would be postdoc who is now at the University of cost, capability, and numerical density,” another kind of procedure that would he explains. Minnesota, has worked on the biogive you three-dimensionality and some There is “a genuine interest on the mimetic assembly of electronic devices other interesting features, starting from part of the microelectronics [industry] (Proc. Natl. Acad. Sci. U.S.A. 2002, a planar technology.” a in self-assembly as a method of making 99, 4937– 4940). He says the use of —Rajendrani Mukhopadhyay real devices,” Whitesides says. For incrimped tape is a notable advance be© 2006 AMERICAN CHEMICAL SOCIETY
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