Abstract
Silver particle-free inks are under rapid development due to their unique properties. Currently, most of the developed silver particle-free inks contain multiple components. In addition to the necessary solvents and silver precursors, these inks also contain complexing agents, reducing agents, and various additives. While such complex compositions assure good stability and printability of the inks, they hamper the sintering process as excess time and energy are often required to remove residues from various compositions to ensure high conductivities of the printed structures. Thus, a simple ink system is expected. On the other hand, plasma sintering shows its sintering potential in treating silver particle-free inks, but is only employed for the sintering of silver nitrate or silver acetate-based inks. Consequently, developing new particle-free ink systems with simple compositions and exploring the potential of plasma sintering is very meaningful. In this work, a clear and transparent silver particle-free ink was formulated, which can be treated both by low-pressure argon plasma sintering and low-temperature thermal sintering (120–160 °C). The roles of 2-amino-2-methyl-1-propanol (AMP) in the ink formulation were investigated in detail, which not only acts as the solvent but also as the complexing agent for silver oxalate to lower the sintering temperature of the ink. The electrical performance of the formulated ink was examined for both sintering processes for different conditions. The thermal sintering resulted in a resistivity value of 24.3 μΩ·cm on glass substrates after treatment at 160 °C for 60 min, while the plasma sintering yielded a resistivity value of 29 μΩ·cm at 500 W for 30 min. Compared to thermal sintering, plasma sintering achieved a similar electrical performance, but with a more nonuniform film structure. The power, sintering time, and the pressure of argon are key factors responsible for the conductivity of the produced films. Nevertheless, both resistivity values do meet the minimal electrical requirements of most electronic applications.
Highlights
The fabrication of good conductors on low-cost substrates has been the research focus of flexible electronics
The thermal sintering resulted in a resistivity value of 24.3 lXÁcm on glass substrates after treatment at 160 °C for 60 min, while the plasma sintering yielded a resistivity value of 29 lXÁcm at 500 W for 30 min
Each plasma sintering experiment consisted of the following steps: (1) The chamber was evacuated to a pressure lower than 0.1 mbar; (2) argon gas was introduced into the chamber at a controlled flow rate (0.2 sccm) that was maintained for the duration of the experiment; and (3) after the flow rate and pressure stabilized, a plasma was initiated
Summary
The fabrication of good conductors on low-cost substrates has been the research focus of flexible electronics. In addition to the necessary solvents and silver precursors, these inks contain reducing agents, complexing agents, and various additives [14, 15, 21] Such a multi-component ink system presents some limitations: (1) more energy and time are required to remove various organic contents, and the inks need to be processed at high temperatures to achieve a good conductivity that precludes the use of many low-cost flexible substrates; (2) the additives used in the inks (e.g., organic binders) act as defects in the produced metallic film, lowering the conductivity. Both sintering methods can achieve a resistivity in the order of 10–5 XÁcm, which is in line with the targets required for electronic applications
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