Acid-Free Fabrication Creates Longer-Lasting Flexible Displays
DAEGU, South Korea, April 14, 2015 — Hybrid organic-inorganic thin films for flexible displays can now be created without the corrosive acids used in conventional sol-gel fabrication.
Developed by researchers at Kyungpook National University, the process begins with a copolymer composed of two organic materials, methyl methacrylate and 3-(trimethoxysilyl) propyl methacrylate. These two materials are then combined with trialkoxysilane. This resultant copolymer then is reacted with two inorganic chemicals, titanium isopropoxide and tetraethyl orthosilicate, to synthesize hybrid layers with high (1.82) and low (1.44) refractive indexes.
The hybrid thin film undergoes a bending test at minimum width of 40 mm. Courtesy of Soo-Young Park/Kyungpook National University.
Most transparent materials have refractive indexes between 1 and 2. Inorganic, thin-layer and hybrid films all have multiple layers, each of which may have different refractive indexes to help tune the wavelengths of light they transmit. Tests of the new hybrid films indicate that both the high and low refractive index layers are highly transparent – with transparencies of 96 percent and 100 percent, respectively, when compared to bare glass.
The hybrid materials are produced entirely in solution, at low temperatures and without the need for high-vacuum (i.e., very low-pressure) conditions, which significantly reduces production costs. In addition, the process allows for the creation of multilayered films in which layers have thicknesses that would allow their use in antireflection coating.
Additionally, in contrast to inorganic layered films, the hybrid films showed less depreciation in flexibility after 10,000 bending cycles. The resistance of these materials increases due to the formation of minuscule cracks that occur as they flex. A film with higher resistance has lower electrical conductivity, meaning that more voltage must be applied to send a signal through it, which further degrades the material.
As for the new material, “The resistance increases less over time in the hybrid thin-layer film, so a display made from this type of film will last longer,” said Soo-Young Park, associate professor at Kyungpook.
The research was published in Optical Materials Express (doi: 10.1364/OME.5.000690).
For more information, visit www.knu.ac.kr.
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