Low Temperature Plasma Sintering of Silver Nanoparticles for Potential Flexible Electronics Applications
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Low Temperature Plasma Sintering of Silver Nanoparticles for Potential Flexible Electronics Applications Siyuan Ma1, Vadim Bromberg1, Frank D. Egitto2, Timothy J. Singler1 1 Mechanical Engineering Department, Binghamton University, Binghamton, NY 13905, U.S.A. 2 Research and Development, Endicott Interconnect Technologies, Endicott, NY 13760, U.S.A. ABSTRACT Deposition of solution-processed functional materials generally requires additional postprocessing to optimize the functionality of the material. We study sintering of Ag nanoparticle (NP) (with average diameter 77nm) deposits for improved electrical conductivity, with emphasis on Argon plasma methods compatible with the low temperature requirements of regular low-cost flexible polymer substrates. The relationship between plasma parameters (such as power and treatment time) versus sintering results (sintered structure depth, film continuity and electrical sheet resistance) will be reported. According to our efforts so far, we have achieved the electrical resistivity of the sintered film at about 20 times greater than the value of bulk silver using a process compatible with the low temperature requirements of common flexible polymer substrates. INTRODUCTION The development of roll-to-roll (R2R) large-scale manufacturing for fast and low-cost fabrication of flexible electronics requires contribution from four research fields: substrate materials[1], functional materials[2]), the material deposition process, and final treatment to enhance functionality of the deposited material. Many solution-based deposition methods of functional nanoparticles have already been widely studied and adopted (such as inkjet printing[3], slot die coating[4] and gravure printing[5]) to be used with low-cost flexible plastic substrates such as polyethylene terephthalate (PET). However, challenges still exist in the postdeposition step. For instance, a deposited film of metal nanoparticles consists of two discrete phases – the metal particle core and the organic capping layers which are incorporated during the nanoparticle synthesis to stabilize the suspension. To enhance the film’s functionality (i.e., electrical conductivity), a sintering step is necessary to remove the organic capping material and produce a continuous metal phase. Sintering requires conditions of high temperature, harsh chemical environments etc which make the process incompatible with low glass transition temperature substrates such as PET. In this study, radio frequency plasma is used to sinter silver nanoparticle films at low processing temperature. The influence of particle size and thickness of the organic capping layer on the evolution of the sintered film morphology and final electrical sheet resistance is investigated. EXPERIMENTAL DETAILS Silver nanoparticles (AgNPs) were synthesized according to a published protocol[6]. AgNPs were formed by adding silver ammonia complex aqueous solution to Gum Arabic and glucose aqueous mixture at controlled flow rate while rigorously mixing. After reaction, AgNPs with averag
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