MODs vs. NPs: Vying for the Future of Printed Electronics

Abstract

This Minireview compares two distinct ink types, namely metal-organic decomposition (MOD) and nanoparticle (NP) formulations, for use in the printing of some of the most conductive elements: silver, copper and aluminium. Printing of highly conductive features has found purpose across a broad array of electronics and as processing times and temperatures reduce, the avenues of application expand to low-cost flexible substrates, materials for wearable devices and beyond. Printing techniques such as screen, aerosol jet and inkjet printing are scalable, solutionbased processes that historically have employed NP formula-tions to achieve low resistivity coatings printed at high resolution. Since the turn of the century, the rise in MOD inks has vastly extended the range of potentially applicable compounds that can be printed, whilst simultaneously addressing shelf life and sintering issues. A brief introduction to the field and requirements of an ink will be presented followed by a detailed discussion of a wide array of synthetic routes to both MOD and NP inks. Unindustrialized materials will be discussed, with the challenges and outlook considered for the market leaders: silver and copper, in comparison with the emerging field of aluminium inks.

Molecular copper decomposition ink for printable electronics

“…12 This is further exacerbated on the nanoscale due to higher surface energies, resulting in greater potential for oxidation. 11,15,16 The potential for oxidation over time greatly limits the stability, reliability and printability of copper nanostructures. Another avenue for printable metal features would be to utilize molecular ink materials instead.…”

“…3,[17][18][19][20][21] Unlike the nanostructures, molecular inks do not oxidize as they start as ions (such as Cu 2+ instead of Cu 0 ). 16,22 However, typical molecular inks suffer from having low concentrations and organic volatile solvents. In spite of these drawbacks, expanding the use of molecular inks can provide new avenues for printable electronics.…”

“…In spite of these drawbacks, expanding the use of molecular inks can provide new avenues for printable electronics. 3,16,[18][19][20][21] In this study, we explore printable and air-stable molecular copper ink materials from metal-organic decomposition (MOD) by using copper ions, including both copper formate (Cu-F MOD) and aqueous copper formate amine complex materials (Cu-A MOD). The decomposition temperature of Cu-F can be reduced by complexing with amines, allowing for lower temperature compatibility with paper and polyester-based flexible electronics.…”

“…In spite of these drawbacks, expanding the use of molecular inks can provide new avenues for printable electronics. 3,16,18–21…”

High‐Resolution 3D Printing for Electronics

“…MOD inks usually contain lower concentrations of metal than metallic nanoparticle inks, but the omission of nanoparticle processing makes it cost-effective. [33][34][35] Compared with the metallic nanoparticle inks, sintering at low temperatures was achieved because there were no colloidal stabilizing agents. This prevents the oxidation of metallic particles, which occurs when the high-temperature sintering is done.…”