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EETE JULAUG 2013

Fig. 3: Product positioning of p-FLEX for flexible displays. Table 1: Comparing potential semiconductors for flexible displays. semiconducting binders. These binders are specifically designed to control the phase separation of the small molecule such that it deposits in its high performance microstructure at the desired device interface. These inks enable top gate devices having a high concentration of the polycrystalline material at the air interface and bottom gate devices with a high concentration of the high mobility small molecule at the dielectric interface. The p-FLEX range of semiconductor inks now consist of a range of high mobility polycrystalline small molecules in combination with seven distinct chemical classes of customised semiconducting polymers, these are the subject of a series of unpublished patent applications. When it comes to performance, these inks have been rigorously tested both internally and externally at centres of excellence such as CPI in the UK and by industrial partners (and offers (for TGBC TFT’s) charge mobility in excess of 5 cm2V-1s-1, threshold voltages near zero and on-off ratios of the order of 105 for un-isolated devices. These solution-based semiconductors thus outperform a-Si and are comparable to most oxides, but with the key advantage of inherent flexibility and ambient temperature processing - a “must have” for most flexible plastic substrates. In addition, initial pilot line trials are exhibiting excellent levels of TFT uniformity due to ability to control film formation at a molecular level. The electrical and physical specifications of this new range of semiconductors already meet the requirements for both EPD and OLED and can be processed on a wide range of material surfaces, such as glass or plastic using print processes such as ink jet, slot die or roll-to-roll. Critically this offers the end user the potential to make the transition to continuous print techniques and reduced cost of production as these systems come online. In the short term, new curved form factor product in the next six to twelve months will most likely incorporate low mobility, high temperature inorganics on glass via a legacy of traditional kit and materials. However whilst inorganics are a quick fix to the very immediate need for new product, the medium to long term needs of the flexible display industry will inevitably move towards low temperature, solutionbased organics where the material performance and process advantages are just too compelling to ignore. For instance an organic front plane coupled with an organic back plane makes sense, especially when you throw into the mix the potential for continuous roll to roll production. Fig. 4: SmartKem p-Flex (spin coat) solutions. www.electronics-eetimes.com Electronic Engineering Times Europe July/August 2013 33


EETE JULAUG 2013
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