Exothermic and Recursive Reaction of Self-Sinterable Silver Ink for Flexible Electronics
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Exothermic and Recursive Reaction of Self-Sinterable Silver Ink for Flexible Electronics Dong-Youn Shin1 and Sangki Chun2 1 Department of Graphic Arts Information Engineering, Pukyong National University, Busan, 608-739, Republic of Korea. 2 Information and Electronic Materials Institute, LG Chem Research Park, Daejeon, 305-380, Republic of Korea. ABSTRACT For the construction of highly conductive printed electrodes on a polymeric substrate with a low glass transition temperature, the development of a low temperature sinterable conductive ink has been a crucial issue in printed electronics and display applications. In this work, we introduce a novel type of self-sinterable silver ink, whose sintering is triggered at a low temperature and completed with the aid of its own exothermic reaction, and propose its exothermic reaction mechanism. Although individual components of this self-sinterable silver ink, Ag2O and silver carboxylate, exhibit endothermic behaviors, their mixture form shows a strong exothermic reaction when heated at 150 °C. It is found that the dissociated form of the used silver carboxylate contributes to the reduction of Ag2O to Ag through its recursive reaction and produces silver nanoparticles. The major source of an exothermic reaction results from the nucleation and fusion of silver nanoparticles. INTRODUCTION As the era of flexible electronics and displays comes, printing techniques have been paid attention to fabricate highly conductive electrodes for flexible touch screen panels [1]. To implement printing techniques on a flexible substrate with a low glass transition temperature, the development of a low temperature sinterable conductive ink is essential. Therefore, silver nanoparticles have been extensively utilized due to their melting temperature reduction and environmental stability from oxidation [2]. However, silver nanoparticles have a strong surface reactivity to form particulate agglomerates. To prevent such unwanted metallic agglomerates, they have to be capped with a dispersant but its high thermal decomposition temperature might compromise the benefit to use metallic nanoparticles to lower down sintering temperature, as shown in figure 1. As a result, conductive ink without a dispersant is desirable. Moreover, it is noteworthy that the heat energy to convert conductive ink to a metallic film has been supplied from the outside. It is conceivable that the required sintering temperature could be significantly lowered if conductive ink itself generates heat. The mixture form of silver oxide and silver carboxylate was proposed as self-sinterable conductive ink [3,4]. The source of heat was proposed to be an exothermic thermal decomposition of the used silver carboxylate such as silver acetate [4]. However, silver oxide ink with silver 2,2-dimethyloctanoate exhibits a strong exothermic reaction, although silver 2,2dimethyloctanoate itself does not exhibit exothermic thermal decomposition. Therefore, the source of a strong exothermic reaction between silver oxide and silver carboxylate do
