Roll-to-roll production of transparent conductive films using metallic grids
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Introduction The principle of printed electronics involves the use of printing processes to apply liquid inks made from electrically conducting, semi-conducting, and insulating materials in several superimposed layers on plastic films.1 The printing is carried out according to a specified design in order to create electrical components and circuits. These are used in applications such as radio frequency identification (RFID) tags. Therefore, fast and high-volume roll-to-roll production processes allow for the manufacturing of low-cost RFID tags for new mass applications.2 This technology is also used for other applications such as display elements, solar cells, and complex systems known as smart objects. The term “printed smart objects” refers to a combination of various printed electronic components, such as input elements in terms of switches, displays, energy sources such as batteries and solar cells, sensors, and control electronics. Combinations of these individual components enable a wide range of new applications. Thus, for example, by combining a printed battery with a logic circuit, an input element and a display, it is possible to construct disposable sensors, games, or information displays.3 The possibility to print new functional materials on large and flexible substrates is opening up many markets for new applications in areas where conventional (inorganic) electronics have limited or no access. The main advantage of printed electronics is that all the necessary components for integrated circuits and RFID tags
can be printed within the same layer structure. Therefore, the production of all components for a RFID tag, for example, can be realized on a flexible plastic substrate using the roll-to-roll principle and requires only a few printing steps. In order to develop a roll to roll process for printed electronics successfully, many different requirements have to be met, especially with respect to material, process, design, and testing properties. All materials must have adequate functionality, stability, and long-term availability at high quantity and low price. A suitable printing process requires a high production speed and must also be possible at temperatures well-below 120°C and with short drying times below 30 seconds. Furthermore, only non-toxic and non-explosive materials and solvents can be used in these processes.4
Conductive transparent films An example for the potential of printed electronics is the development of a printed transparent conductor utilizing a metallic grid by PolyIC GmbH & Co. KG. Figure 1 shows a photograph of the conductive and highly transparent PolyTC film. These printed grids were enabled through the printing process developed for RFID tags, in which many organic field-effect transistors with high functionality are required. High functionality, for instance, can be achieved with very high resolution, meaning a very small structure size of the lower electrode (source and drain electrodes, see Figure 2). Over the last few
Jasmin Woerle, PolyIC, Germany; [email protected]
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