Antonius Wilhelmus Maria De Laat

Inkjet-printed silver tracks : low temperature curing and thermal stability investigation

In this contribution the curing behavior and conductivity development of several commercially available silver inks is discussed. In addition, the preparation and characterization of a silver particle ink that shows a curing temperature as low as 80 °C is described. Good to excellent conductivity values of 5 to 56% of bulk silver have been reached by using a very small amount of organic additives without any strong adsorbing groups such as amines, amides or mercapto groups. This low curing temperature opens new routes to produce conductive features on polymeric foils that have a low Tg, like PET. Furthermore, the temperature stability of silver tracks, prepared by inkjet printing different colloidal silver suspensions, was investigated. Hereto, the resistance was on-line measured during heating of the silver tracks, from room temperature to 650 °C.

One-step inkjet printing of conductive silver tracks on polymer substrates

A one-step process to fabricate conductive features on flexible polymer substrates by inkjet printing an organometallic silver ink directly onto a substrate that is heated to 130 degrees C is presented. This process led to the immediate sintering of the printed features. The samples were left for 5 min at elevated temperature, which resulted in conductive silver features with a resistivity of eight times the bulk silver value. The combination of this ink and the simultaneous printing/sintering process opens up routes for the direct fabrication of conductive features on common polymer substrates that could be applied, for example, in roll-to-roll production of flexible microelectronic systems.

Geometric control of inkjet printed features using a gelating polymer

When an inkjet printed feature is formed, the behaviour of the ink on the substrate is of great importance. In order to investigate the possibility of increased control over the as-printed feature on a substrate, a TiO2 ink was formulated that gels above a certain temperature. The TiO2 particles in the ink are colloidally stabilised by an adsorbed layer of poly(vinyl methyl ether)-block-poly(vinyloxy-4-butyric acid) diblock copolymer. The thermal gelation, at about 37 °C, is due to the limited solubility of the poly(vinyl methyl ether) buoyant block in the continuous medium of the ink. Drops and lines with improved morphological control and resolution were achieved using the thermal gelation effect. Lines printed using this approach did not display deviations at their starts and ends; and bulges in the line could be avoided. Finally, defect-free straight lines could be printed on very hydrophobic surfaces, which is impossible with regular inks due to the de-wetting nature of such substrates.