Nanoparticle sintering methods and applications for printed electronics

Printed electronics refers to the technologies of fabricating electronic and optoelectronic devices by traditional printing methods. Especially roll-to-roll mass-printing is foreseen to enable low-cost devices on flexible substrates. Direct-write patterning methods, such as inkjet printing, inspire potential for cost-savings in R&D prototyping and customization. Various organic and inorganic materials can be printed in liquid form and subsequently cured to obtain desired electric functionalities. For example, metals can be printed as nanoparticle dispersions and sintered to obtain high conductivity. In this Thesis, the applicability of silver nanoparticle inks for printed wiring, interconnections, memories, antennas, and wireless resonant tags, is investigated. The Thesis work involves modeling, simulating, fabricating, measuring and analyzing the prototype structures. Novel methods for sintering nanoparticles are developed. The rapid electrical sintering method, performed by applying voltage over the printed structure, is shown to provide a conductivity increase of more than four orders of magnitude in just milliseconds with the resulting conductivity reaching above 50 % that of bulk silver. The method is further developed to allow for a more practical adaption via contactless coupling at microwave frequencies. A room-temperature sintering method based on the chemical removal of the nanoparticle stabilizing ligand through interaction between the ink and the coating layer of the printing substrate is also presented. The substrate-facilitated sintering method is shown to enable in situ component attachment to printed structures. Inkjet printed RFID antennas and a wireless RF resonant tag fabricated by a combination of roll-to-roll gravure and inkjet printing are shown to provide reading distances sufficient for many practical applications. A novel approach for contactless read-out of printed memory is introduced and demonstrated for a memory structure inkjet printed using silver nanoparticle ink. The information content of the memory is stored in memory bits selectively programmed using the rapid electrical sintering method.