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Posted: Sep 04, 2013

Using nanoimprint lithography to develop highly rugged and lightweight liquid crystal displays

(Nanowerk News) Displays for smartphones or tablet-PCs should be highly ruggedized at little overall weight. For curved displays, that might play a role in advertising or the automotive sector, a certain flexibility of the display materials is mandatory. Together with national and international industry partners, scientists at the University of Stuttgart have started the development of very robust and extremely lightweight displays within the research project LiCRA. Instead of common glass substrates these displays are based on plastic foils what makes them flexible. The overall market for rugged displays is estimated to a total of seven billion (milliard) US$ until 2015 .
Partners of the LiCRA consortium other than the Institute of Large Area Microelectronics of the University of Stuttgart are the British company plastic logic, the Israelian company Etkes and sons, the south German company LOFO High Tech Film GmbH from Weilheim am Rhein, micro resist technology GmbH from Berlin and as an associated partner the pharmaceutical, chemical and life-science-company Merck KGaA from Darmstadt. The project is scheduled for 30 month and is funded with a total of 1.5 million Euros by the German federal ministry of science and education and the national funding agencies of the international partners, respectively. Together with Plastic Logic, scientists of the University of Stuttgart will develop a process flow for the assembly of liquid crystal cells on plastic.
For this purpose Plastic Logic will advance and adapt its organic thin film transistor (OTFT) technology, which has been used for monochrome e-paper displays so far. The actual mounting process for the liquid crystal cells will be developed at the University of Stuttgart. Challenges for these developments are in particular the necessity to work in the low temperature regime as well as the flexibility of the substrates. In addition, the University of Stuttgart investigates the production of organic light emitting diodes (OLEDs) with polarized light emission. Such OLEDs would be advantageous in that way that an additional backlight and one of the two polarizer sheets, which so far are necessary for liquid crystal cells, could be omitted.
Etkes and sons will develop a back light unit (BLU), which fulfils the requirements of a rugged and lightweight display.
micro resist technology GmbH will develop materials and processes for nano imprint lithography. While the production if microelectronic structures with classic lithography means exposure of a photo resist with UV light and subsequent development of the resist, in nano imprint lithography the desired structures are directly transferred to an adequate nano imprint resist by the use of a mould. Within the LiCRA project, the use of this technology, which promises not only reduces production cost but also increased display resolution, will be investigated in the process chain of OTFTs on plastic substrates.
LOFO High Tech Film will develop the plastic films required for the realization of the liquid crystal displays. Special attention will be paid on low deformation during the successive production of the liquid crystal displays as well as minimized optical birefringence as both would degrade the optical performance of the displays. The solvent casting process used by LOFO is especially suitable for this purpose because the polymer solution can be filtered extremely fine, the films are barely stretched and are thus almost strainless.
Source: Universität Stuttgart
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