Concepts of metal-organic decomposition (MOD) silver inks for structured metallization by inkjet printing
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Concepts of metal-organic decomposition (MOD) silver inks for structured metallization by inkjet printing Claudia Schonera, Stephan F. Jahna, Alexander Jakobb, Thomas Blaudecka, Heinrich Langb, Reinhard R. Baumanna a
Institute for Print and Media Technology, Digital Printing and Imaging, Chemnitz University of Technology, 09107 Chemnitz, Germany; b Institute of Chemistry, Inorganic Chemistry, Chemnitz University of Technology, 09107 Chemnitz, Germany. ABSTRACT In this contribution, we report on the optimization of a metal-organic decomposition (MOD) ink based on silver(I) complexes by a systematic variation of the ink formulation. As a result, three different ink concepts turned out to be printable and resulting in a sufficiently high contour definition, layer homogeneity, and conductivity. The ink concepts include increase of the solid load, the usage of N-methyl-2-pyrrolidone (NMP) as a humectant with low vapor pressure, addition of co-solvents such as diethylene glycole and addition of sodium lauryl sulfate (SLS) as stabilizing ligand. It turns out that, for silver precursor concentrations of 40 wt%, the addition of 1 wt% SLS to aqueous inks leads to elevated conductivity up to 3.2x107 Sm-1 at maintained printability and an improved contour definition with respect to pure aqueous inks. INTRODUCTION Inkjet printing has gained growing interest in the field of electronics for the manufacturing of electronic devices such as circuitry, light-emitting diodes or solar cells [1]. As passive wiring components are essential for almost all applications of printed and large-area electronics, the patterned metallization of flexible substrates at ambient conditions is a key technology step for any cost-effective manufacturing. In particular, drop-on-demand piezo inkjet has become a focus of research as it is a purely additive technology which allows a precise deposition of smallest volumes (pL range) at places where they are needed. In principle, two different ink concepts can be applied for structured metallization by inkjet printing: nanoparticle inks and metal-organic decomposition (MOD) precursor inks. Both concepts have in common that an inorganic material is dispersed or solubilized with help of organic molecules to form an ink stable enough for the liquid-phase deposition. This step is followed by a subsequent thermally or alternatively initiated chemical reaction to form the metallic layer. The limits of this manufacturing concept are obvious in the light of the increasing importance of substrates with low thermal stability (e. g. polyethylene terephthalate, PET) which have gained interest for flexible electronics applications. In this respect, MOD precursor inks containing dissolved precursor molecule are assigned a benefit over nanoparticle inks as they do not give rise to sedimentation and agglomeration processes in the inkjet nozzle and thus are beneficial for the reliability of the process [2]. Silver(I) complexes have been known since earlier times for thermographic and photothermic imaging [3]. Recently, Jakob
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