Printed electronics : analog and digital signal processing
Date of Issue2014
School of Electrical and Electronic Engineering
Printed electronics (PE) on flexible substrates (e.g. plastic-film) is an emerging technology that is likely to complement the ubiquitous silicon-based electronics. It is frequently touted as ‘Electronics Everywhere, Big Opportunities’, often envisioned as a ‘printing press’ capable of realizing ‘green’ electronic products whose attributes include On-Demand (print quickly, anywhere and anytime), Scalability (large format, e.g. wallpaper), and Flexibility (printed on flexible substrates such as plastic, etc.) such that they can be molded or bent to fit in odd and uneven spaces, yet so inexpensive that they can be everywhere print media is used (cost in terms of cents, and hence disposable). The broad objectives of this multidisciplinary Ph.D. program are to investigate, design and realize PE analog and digital circuits and systems on flexible substrates, thereby augmenting ‘intelligence’ thereto. Specifically, this research focuses on the second and the third chains of the supply chain of the emerging PE technology: printing (processing/equipment platforms) and circuits, respectively. A number of contributions are made herein. First, a novel simple Fully-Additive printing process – a screen printing process – involving only depositions, for realizing PE circuits and systems on flexible plastic films is proposed. This process is Green, On-Demand, Scalable and Low-Cost, congruous to aforesaid envisioned PE ‘printing press’ (vis-à-vis Subtractive printing, a complex process involving deposition and etching that otherwise requires expensive/sophisticated specialized IC (integrated circuit) fabrication facilities and is hence Un-Green, Not-On-Demand, Un-scalable and High-Cost). The proposed Fully-Additive process features printed transistors with high (~1.5 cm2/Vs) semiconductor carrier-mobility, ~three times higher than competing state-of-the-art Fully-Additive processes and comparable to Subtractive processes. Furthermore, the proposed Fully-Additive process is capable of realizing a full array of passive elements, including capacitors, resistors, and inductors, and at least two layers of metal-interconnect. To the best of the author’s knowledge, the proposed process hitherto is the only Fully-Additive process capable of realizing complete and complex circuits and systems on flexible plastic films. Second, a comprehensive open-platform for the proposed Fully-Additive screen printing process to facilitate the design and realization of PE analog and digital circuits is proposed. The proposed open-platform embodies a novel printed transistor model that is simple, accurate and compatible with industry-standard IC electronic design automation tools. To the best of the author’s knowledge, the proposed model is the only model that accommodates and accurately models the effect of the channel length on carrier mobility, leakage current and parasitic capacitances, and is valid for all transistor operating regions, from cut-off to supra-threshold. The proposed open-platform further embodies, to the best of the author’s knowledge, for the first time, process variations (statistical data) and matching based on various layout techniques of the printed transistors. These comprehensive models are imperative for the practical design and simulation of PE circuits, including manufacturability and implications with respect to the challenges of PE circuits. Third, on the basis of the proposed open-platform, several analog and digital circuits are designed, Fully-Additive printed and measured. These circuits include conventional and proposed differential amplifiers, inverters and oscillators. The measured parameters of the printed circuits agree well with that obtained from simulations (using the open-platform derived herein), depicting the efficacy of the open-platform. The Fully-Additive printed proposed amplifier embodies a novel feedback with both positive and negative paths to simultaneously significantly improve the gain and reduce susceptibility to process variations, yet without compromising the printed area (compared to the conventional three-stage amplifier). It is also benchmarked against reported realizations (all Subtractive-based processes), and are shown to be highly competitive despite its realization based on our simple low-cost Fully-Additive process.
DRNTU::Engineering::Electrical and electronic engineering::Integrated circuits