Inkjet printing: technique and applications for organic electronic devices

Since the discovery of the polyacetylene conductivity in 1977 by Shirakawa,MacDiarmid and Heeger, Organic Electronics has been growing and establishing for a new generation of electronic devices. On one hand, the unique properties of polymeric semiconductors and conductors, such as flexibility and transparency, allow the fabrication of low-cost devices over large area: the most common are the Organic Light Emitting Diodes (OLEDs) and the organic photovoltaic cells. On the other hand, much effort has been made to investigate new technologies and processes for the realization of high-performance organic transistors and sensors. Among them, Inkjet Printing is a promising technique which exploits all the advantages of organic materials, such as low-cost and solution processability, and allows the large-scale automated fabrication of large area devices. This thesis describes the work carried outwith a piezoelectric drop-on-demand inkjet printer, theDimatixMaterials Printer 2831. The first chapter gives an overview on Organic and Printed Electronics state-of-art, also describing the physical principles of conductivity in organic molecules. The second chapter is totally focused on the inkjet printing technique: after a brief description of the printer employed, a detailed description of the printing process, from the ink formulation to the drop deposition and drying phenomena, is presented. Moreover the materials employed are described together with the printing parameters set for achieving the best deposition condition. Chapter 3 is devoted to tactile sensing, which is the main application of the Organic Field-Effect Transistors (OFETs) in this work within the ROBOSKIN project. After an overview of inorganic tactile sensors and of the fundamentals of strain sensing in OFETs, the fabrication steps are described followed by the detailed electromechanical characterization of the various strain sensors realized. Finally, the fourth chapter describes other applications of inkjet printing developed in this work: organic diodes and photodiodes within the HYMEC project, patterned electrodes for the detection of cells electrical activity, both in vivo and in vitro, and a RFID tag antenna.