Flexible Electronic Technologies for New User Interfaces
Creators: name: Bairaktaris, Georgios
Publisher: name: University of Surrey
Year: 2023

description: In this work, the use of flexible and printed electronics for novel, real-life user interfaces with unconventional form factors was investigated. This was completed in three stages:<br>
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description: A. Augmented paper platform using hybrid integration: <br>
description: The solutions in the literature for augmented paper were reviewed and analysed, to create the Magic Bookmark, an interaction ecosystem that progresses the state of the art. Flexible Hybrid Electronics that combine conventional off-the-shelf parts with flexible printed conductors were used to iteratively design the Magic Bookmark, with a focus on improving the manufacturability, sustainability, and interactivity of the existing solutions. Dispenser and inkjet printing were used to create flexible conductive circuits, and standard solder paste reflow techniques were used to integrate conventional electronics. The optimal solution for augmented paper relied on a series of reflective optical sensors responsible for detecting a unique contrast pattern printed on each open page spread of a book. The use of proprietary inks supplied by PrintColor improved the system’s integration further by making the contrast pattern semi- transparent to the reader. <br>
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description: B. Development of solution processed, printable photoconductors: <br>
description: To progress the above system towards a fully printed system, printable photodetectors were developed. A planar metal-semiconductor-metal architecture was realised using direct current sputtering of Ag, and spin coating of oxide or organic semiconductors to create photoconductors that were then measured using an external voltage bias. For the oxide implementation, Aluminium-doped ZnO was used, and for the organic implementation a bulk heterojunction was formed using PCDTBT and PCBM. The organic devices that performed better within the visible range sustained at least 100 1???? radius bending cycles, and could be used for open-page detection in the Magic Bookmark ecosystem with error rates under 5% and noise margins of 1.5% at 5?? bias.<br>
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description: C. Fully printed implementation of photodetectors: <br>
description: The above photodetectors were then implemented using fully printed techniques. Inkjet printing was used to deposit Ag interdigitated electrodes on a PEN substrate and pulse-air dispensing was used to form a semiconductor bank with Teflon and subsequently dispense approximately 400???? of the PCDTBT:PCBM blend. The performance of the photodetectors in terms of ON/OFF ratio was comparable to the solution-processed devices and their printability allowed for their direct integration on a flexible strip using evaporated parylene as an insulator between the conductive layers. Finally, the semiconductor blend was optimised through a combinatorial optimisation process that compared different material ratios between the PCDTBT and the PCBM components of the blend against different semiconductor thicknesses created by varying the amount of semiconductor solution dispensed within the Teflon bank. This experiment verified that the original 1 layer of 1: 4 PCDTBT:PCBM blend yields the optimal results for this application.<br>
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description: In summary, this work demonstrates how the advantages of emerging fabrication techniques can be utilised by designing purpose-built solutions around well-defined application requirements. This approach shows that even extremely simple fabrication techniques and comparatively low-performing material systems can be viably utilized in large area flexible electronic applications, with the prerequisite of a system definition that critically considers both the advantages and the limitations of the functional devices.<br>