The conductive properties of ink coating based on Ni–Ag core–shell nanoparticles with the bimodal size distribution

Journal of Materials Science: Materials in Electronics (2020) 31:12991–12999 https://doi.org/10.1007/s10854-020-03852-3 The conductive properties of ink coating based on Ni–Ag core–shell nanoparticles with the bimodal size distribution Anna Pajor‑Świerzy1 · Radosław Pawłowski2 · Piotr Warszyński1 · Krzysztof Szczepanowicz1 Received: 21 April 2020 / Accepted: 20 June 2020 / Published online: 4 July 2020 © The Author(s) 2020 Abstract We studied the conductive properties of ink coatings composed of a mixture of Ni–Ag core–shell nanoparticles (NPs) at the size 70 nm and 250 nm. The metallic ink films were deposited on glass substrates by using bar coating and screen printing methods. The effect of the type of deposition method of ink coatings, as well as the temperature and time of the sintering process on their conductivity, was investigated. The most conductive films were obtained after thermal sintering at 300 °C. The obtained conductivity was about 20% of that for a bulk nickel, more than 80% higher than for films formed with any single type of particles. 1 Introduction The ongoing process of miniaturization and complexity of electronic devices requires searching for proper conductive materials. Therefore, in the last years, the methods of their preparation and application in the electronics industry have been extensively studied. In this context, conductive inks based on metallic nanoparticles (NPs) have attracted much attention. Currently, one of the most promising method of the fabrication of electronic circuits and devices is a printed technology, in which conductive inks containing metallic nanoparticles (NPs) are deposited on solid and/or flexible substrates for production of solar cells, thin film transistors, printed circuit boards, transparent conductive electrodes, flexible displays, electrochromic devices, or touch screens [1–3]. To formulate the conductive inks, several approaches have been used so far. They can be produced from organometallic compounds or conductive polymers, colloidal suspensions of metallic nanoparticles, or some combination of these components [4]. The conductive inks based on metallic NPs, due to their low melting point and * Anna Pajor‑Świerzy ncpajor@cyf‑kr.edu.pl 1 Jerzy Haber Institute of Catalysis and Surface Chemistry, Polish Academy of Sciences, Niezapominajek 8, 30‑232 Kraków, Poland 2 Abraxas Jeremiasz Olgierd, ul. Piaskowa 27, 44‑300 Wodzisław Śląski, Poland high conductivity, are the most promising for the preparation of printed electronic circuits and devices. Particularly, silver or gold nanoparticles as high-performance electrical conductive materials, have been most commonly applied so far in the preparation of ink formulations [5–7]. Although silver and gold NPs have apparent advantages such as low resistivity and stability against oxidation process, they are expensive to use commercially. Besides, while using silver, the electro-migration process could lower the reliability of an electrical circuit. The high price of Ag NPs and the increasing requirements of reducing the production cost of electronic devices have led to searching for alternative nanopigment for conductive ink preparation. Therefore, nickel nanoparticles [8, 9] are considered as a suitable replacement of gold and silver nanoparticles due to high conductivity, low price and diminished electro-migration process. The challenge with Ni NPs is their rapid oxidation in the atmospheric environment. Oxides are not conductive which delimit Ni NPs application in printed electronics fabrication. Therefore, the synthesis of Ni NPs, as well as conductive ink fabrication, requires the protection of those nanoparticles against the oxidation process. Coating the surface of Ni NPs by a silver layer, which results in the formation of nickelsilver core–shell structure, is an effective, fast and simple method to retard the oxidization process of the nickel core [10, 11]. Conventional methods of the fabrication of conductive tracks or electronic devices such as photolithography, vacuum deposition, and electroless plating processes have many disadvantages. They are multi-stage, expensive, and 13 Vol.:(0123456789) 12992 produce large amounts of waste. Therefore, in the last years, the alternative methods of manufacturing of conductive materials have been searched. One of the fast and low-cost methods of deposition is bar coating, which provides a simple but effective application of paints, printing inks, lacquers and other surface coatings onto many substrates, including paper, plastic films, foils, metal plates, glass plates, etc. In a single operation, two or more layers can be applied side-by-side, which makes the technique ideal for comparing products [12, 13]. Another alternative deposition method is the screen printing of pastes composed of metallic micro- or nanoparticles. This technique is also fast and straightforward. It involves only two steps: printing and curing of the deposited pattern [13–15]. The main disadvantage of screen printing is the large amount of required ink, which generates high costs. The process of formation of well-connected metallic nanoparticle networks in ink coatings is usually prevented by the presence of stabilizers and other ink composites (wetting agents, binders, defoamers, etc.), which create isolating layer between nanoparticles. Therefore, after the ink coating, the removal of the protective layer by post-coating treatments is usually required. To transform nonconductive ink coating into a conductive one, metallic nanoparticles need sintering to form a continuous network with direct contact between them. The unique properties of nanoparticles, such as high surface-to-volume ratio and enhanced self-diffusion of surface atoms, decrease their melting point [16, 17]. Therefore, the sintering temperature can be much lower than in the case of bulk material [18, 19]. The sintering process involves three stages and depends on the temperature and time of heating. The first stage significantly depends on the conditions of the process (the shorter time requires the higher temperature). In the second stage, which is important to obtain a high conductivity, the removal of the insulating protective particle layers and a dynamic change of the sheet resistance can be observed. In the last stage of sintering, the value of resistance is only slightly changed in a long time (a few hours) of heating. The sintering conditions play a significant role because they determine the conductivity of the coated films and the applicability of particular substrates. Therefore, they are important from the application point of view. Besides of sintering conditions, nanoparticles properties such as particle size and shape influence on the final conductivity of deposited ink layer [16, 17]. Among them, particle size is one of the most important for ink coating to obtain high conductivity. The nano-size effect decreases the melting temperature of the metal (...truncated)