New Frontiers in Smart Sensors Based on Printed Organic Electronics

Abstract

Organic printed electronics is an attractive platform to develop mechanically flexible and cost-effective solutions for innovative applications such as foldable displays, flexible sensing surfaces, or biomedical instrumentation that can adapt to the shape of the body. Despite the growing interest and the recent advancements of printed electronic technologies, their use in commercial products remains very limited till now. Processing challenges such as limited yield, large transistor variability, and poor electrical performance still prevent printed systems-on-foil from commercial exploitation. The approach proposed in this work aims to tackle several of these limitations at different levels of abstraction, starting from the fabrication process and reaching the system-on-foil design. From the processing side, the major mechanisms leading to defects in a gravure-printed unipolar Organic Thin-Film-Transistor (OTFT) technology have been identified, and a successful approach to improve both device yield and performance has been developed. The availability of a reliable transistor technology is indeed a key requirement to enable complex systems-on-foil with high-yield. Assisted design flows and reliable Process Design Kits (PDKs) are also a fundamental asset to simulate and predict the system performance, further improving yield and significantly reducing design time. For these reasons a complete PDK specifically suited for gravure printed technologies has been developed. Furthermore, a methodology for the design and transistor-level implementation of analog and mixed-signal systems has been proposed: it aims at minimizing the transistor count, thus maximizing the overall yield. Circuit techniques which make use of ratiometric radouts and passive feedback networks have been used to reduce the sensitivity to the parameter variability and decrease the risks of soft failures in circuits. This multidisciplinary approach allowed us to design and successfully fabricate state-of-the-art printed smart sensors. Flexible solutions for large-area proximity and pressure sensing applications have been demonstrated, using lamination of a foil containing sensing functionality to a foil carrying analog fronted readout electronics. Both fully organic and hybrid organic-Si CMOS electronic approaches have been exploited for the readout and signal conditioning of this class of sensors. Finally, an ultra-low cost printed smart temperature sensor on an RFID tag suitable for cold chain temperature monitoring applications has also been designed and built. These results demonstrate that printed electronics can be successfully used today to fabricate inexpensive smart sensing devices for a large number of applications in which sensing over a large area, mechanical flexibility and cost are important requirements.