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FLEXIBLE ELECTRONICS Organic photo diodes for flexible sensor applications By Christoph Hammerschmidt Enabling the design of cameras with higher sensitivity or test equipment for display panels, organic photodiodes are increasingly regarded as a promising alternative to their siliconbased counterparts. Fraunhofer COMEDD has developed a colour sensor based on organic materials. Organic photo detectors (OPDs) utilize organic molecules to define the light sensitivity within a specific part of the light spectrum. An example for materials suited for OPDs are certain colour pigments. “These devices have multiple advantages over conventional inorganic components”, explained Olaf R. Hild, department manager at Fraunhofer COMEDD in Dresden. Which material suits best however depends on the part of the light spectrum a customer needs for his specific application. Organic materials are only sensitive to light of a certain wavelength, they react only to light of a certain colour. This means that the scientists can control the spectral sensitivity distribution of optical sensors through the selection of the material. Materials available already cover a wide range within the spectrum of visible light. For specific applications in the ultraviolet or near infrared range, the researchers also develop compact microsensors that combine organic semiconductors with silicon technology. The application spectrum ranges from tiny sensor elements in cameras or in bioanalytics to large-area applications in quality control - for instance, such devices can be utilized to determine damages to the paintwork in automotive volume production. Other examples are lab-on-chip applications that detect certain DNA sequences which have been marked with fluorescence markers. And yet another application example: In CCD sensors for sophisticated photo cameras, organic photodiodes can increase the sensitivity to light. “They are more sensitive because they can use a larger active area”, Hild explains. In contrast to silicon sensors, OPDs can be implemented as flexible components. To manufacture flexible devices, the structures for the photodiodes are deposited onto polymer film which in turn can be applied to curved or bulged surfaces. In this manner it is possible to create specific shapes for quality assurance applications into which the device under test can be placed. An example is testing car doors for paintwork damages: The entire door is tested quickly in one single step. This, OPDs are particularly well suited for largearea applications where they offer a significant cost advantage over conventional technologies. It is much more expensive and lavish to coat large curved areas with silicon sensors than with OPDs. Coating such surfaces with OPDs is done in simple processes on relatively cheap materials. Developers can utilise proven manufacturing technologies such as the processes in the production of organic photovoltaics. Interactive packaging to display contextual messages By Julien Happich In retail stores, presentation and packaging design are often key to lure customers into buying products. It is the product’s skin on the shelves, and it is only at a quick glance that consumers will evaluate if they want to pick up the product for closer inspection. Battling for a share of your attention, regular inkjet printing on all sorts of substrates won’t just be enough to compete with tomorrow’s smart packaging technologies. Some manufacturers System-on-foil for measuring and displaying the temperature (© Fraunhofer EMFT). are looking at electroluminescent foils for illumination or decorative purposes, others want to integrate film-based displays into the packaging to bring additional information to the customers. Using flexible or printed electronics, Researchers at Fraunhofer EMFT are now working on the integration of complete electronic systems in foil. The current state-of-the-art technology makes assembling single components and electrical connections on flexible materials possible, but enables only relatively simple applications. At the Interpack trade fair this year, the researchers have demonstrated a flexible temperature measuring system, integrating the sensors, display and flexible batteries into a complete system on foil. Such labels could be used to monitor product freshness and the cold chain during transport and storage. Tie this to an RFID label together with printed memory, and you may be able someday to greet would-be customers with a contextual message (as the product is lifted from the shelve or as a readerenabled cart passes by). RFID labels are progressively being adopted at product level, together with shelf-tied tag readers, to give retailers a real-time feedback on the product’s presence on the shelves, then in the carts for automated checkout and inventory. So this would be combining visual packaging with customer interaction and inventory knowledge. Beyond its pure eye catcher functionality, the package could display updated information about the product’s content, you could even think of time-based game scenarios and product pricing.In its demonstrator, the research lab claims that no rigid and complicated wiring are necessary, all the system’s components are connected to each other via printed interconnects, directly on the same substrate foil. The complete system is thin enough to be easily attached on surfaces of products and packages. At its technology center for flexible electronics, Fraunhofer EMFT claims to have the capability to deliver high-volume production similar to real manufacturing conditions, using reel-toreel technology on a number of substrates such as plastic foils, paper or textiles. The researchers are now looking for research and industrial partners to set up a new production line for application-specific mass manufacturing of flexible electronic components and systems. 26 Electronic Engineering Times Europe June 2014 www.electronics-eetimes.com


EETE JUN 2014
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