Flexible And Stretchable LEDs By Researchers At University Of Illinois

Researcher John Rogers, from the department of material sciences in University of Illinois, has come up with a development in the field of material sciences, the flexible and stretchable LEDs. This new discovery over comes the bulkiness and rigidity of the traditional kind and allows its use in loads of places. They are only 20 microns wide and 2 microns tall and so they are very small. The flexibility and stretch ability of the LED is attributed to this small size. The places of use can range from bumper mounted brake lights, computer and television screens that roll up into a pen to more serious applications like biomedicine applications (light emitting sutures, implantable sheets, illuminated plasmonic crystals) and robotics. These new variants can be bent, rolled and stretched and all long the operation will just not be affected.

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The two existing categories of LEDs are organic and inorganic. The organic ones are small and easy to manufacture but the inorganic ones gain an advantage because of their improved performance compared to the organic ones, though the inorganic ones are tough to create and require high temperatures and hard surfaces. They are more bright and efficient.

The system described has numerous interconnected, inorganic LEDs and photo detectors. Unusual substrates were put to use using optimized layouts so as to give it the flexible and     stretchable properties.  The usual substrates that were demonstrated are fabric, pieces of aluminum foil, leaves, and sheets of paper. In any of the above cases the performance was robust.

They are incorporated with waterproof capabilities so it is possible for them to work when immersed in saline solutions, bio-fluids, chemical fluids.  They are used in waterproof optical-proximity-sensor tapes capable of conformal integration on different curved surfaces.

The process of manufacture of the new kind of LEDs is almost identical to the traditional method with a little change in the layers structure. The process is called the Dual transfer process. The first step, growing of the semiconductor materials onto a temporary surface also called as sacrificial layer. Contacts, interconnections, structural bridges, encapsulations are formed. The next step, transfer printing is done so as to allow integration on elastomeric sheets or any of the other substrates. These substrates must be coated with a thin layer of PDMS with strong bonding only at locations of devices.

The sacrificial layer is placed in between LED layers and wafer layer. So after the etching process is all completed, the sacrificial layer is dissolved away and the LED is removed using a rubber stamp and embedded in plastic, glass or rubber substrates.  It is this versatility of the LED with respect to the substrates that makes it exciting. So the flexible LEDs are indeed something to watch out for.

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