Electrical sintering characteristics of inkjet-printed conductive Ag lines on a paper substrate Shin Jang, Dong Jun Lee, Dohyung Lee, Je Hoon Oh ⁎ Department of Mechanical Engineering, Hanyang University, 1271 Sa3-dong, Sangrok-gu, Ansan, Gyeonggi-do 426-791, Republic of Korea abstract article info Available online 16 May 2013 Keywords: Electrical Sintering Inkjet printing Ag nanoparticle ink Paper substrate Resistivity Initial resistance Grain growth The electrical sintering characteristics of inkjet-printed line patterns on a paper substrate were investigated by varying initial pattern resistance, input voltage, sintering time, and input voltage profile. The initial resistance was controlled by preheating the patterns, and its range was between 500 Ω and 5 MΩ. Depending on the input voltage and initial resistance, there exist three different regions: sintering, no change, and blowout. While no sintering is observed for too high initial resistance, blowout of printed lines occurs for a larger input voltage. For the initial resistance lower than ~100 kΩ and the input voltage ranging from 20 V to 40 V, all the printed lines are electrically sintered within a short time without damaging the underlying paper substrates. When using the two-step voltage profile, the final resistance of lines becomes five times smaller than the resis- tance with the one-step voltage profile due to the increase in the grain size and the reduction in the void area, and no burning or blowout occurs in the lines. Due to its many advantages, the electrical sintering can provide a fast, reliable and effective way to fabricate high quality inkjet-printed conductive patterns for various printed electronics applications. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Over the past few decades, printed electronics has become a prom- ising technique to overcome the drawbacks of conventional lithography for various fields such as thin film transistors [1,2], solar-cells [3], and biosensors [4]. Particularly, inkjet printing technology can be used to di- rectly print dielectric layers, electrodes, and electric circuits without any further processing, resulting in low production cost and a simple and waste-free process [5–8]. Metal nanoparticle ink is widely used in inkjet printing to form con- ductive patterns including electrodes and electrical circuits. Metal nanoparticles are suspended in the solution with an organic binder and dispersing agent. These act as suspending agents to encapsulate metal nanoparticles to prevent agglomeration between the nanoparticles. A post-thermal sintering process is therefore required to form the electri- cally conductive path by removing the agents that prevent conductivity after printing the ink onto the substrate. Due to the high surface-to- volume ratio of nanoparticles, the sintering temperature is much lower than that of bulk materials. While the melting point of bulk silver is about 961 °C, the sintering temperature of nanoparticle silver ink is in the range of 150 °C to 250 °C, depending on the concentration and type of suspending agents and the nanoparticle size. Although the sintering temperature is low, traditional thermal sintering process can cause thermal degradation of underlying soft substrates such as thermal- ly sensitive polymers and papers. Another drawback of the thermal sintering is a long processing time. Therefore, an alternative sintering process that can provide desired electrical characteristics in a fast and ef- ficient way is essential for high-throughput production. To overcome these obstacles, several methods such as light sintering [9], microwave sintering [10,11], plasma sintering [12], laser sintering [13] and coalescence of nanoparticles without heating [14] have been investigated. These methods are still in the development stage and are not proved to be practical for the fast and reliable sintering yet. In this work, we introduced an electrical sintering method combined with a preheating process. For electrical sintering, when the voltage is applied to the printed pattern, the joule heat is generated along the pattern within a very short time. This method is fast and highly selective, and it does not damage underlying substrates. It is also more effective than thermal sintering since only the conductive patterns are heated rather than the entire substrate. The effects of initial pattern resistance, applied input voltage and time, and input voltage profile on the sintering characteristics of Ag lines inkjet-printed on a photo paper were investigated after a preheating pro- cess. The initial resistance was varied by controlling the preheating tem- perature and time. The sintering performances were characterized with a field emission scanning electron microscope (FE-SEM), an optical micro- scope, and an oscilloscope. Various conditions related to stable electrical sintering without defects were discussed in this study. 2. Experimental details Commercial photo paper (HC-4020G, Hansol Co.) with a 230 μm thickness, which can endure up to 120 °C, was used as a substrate. Thin Solid Films 546 (2013) 157–161 ⁎ Corresponding author. Tel.: +82 31 400 5252; fax: +82 31 400 4705. E-mail address: jehoon@hanyang.ac.kr (J.H. Oh). 0040-6090/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.tsf.2013.05.015 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf