Copper(II) ethylene glycol carboxylates as precursors for inkjet printing of conductive copper patterns

• Synthesis and characterisation of metal–organic copper(II) carboxylates
• Decomposition studies by thermogravimetric measurements and mass spectrometry
• Inkjet printing of conductive copper structures on different substrate materials
• High electrical conductivity was obtained without sintering in a reducing atmosphere.

Copper(II) ethylene glycol carboxylates were investigated as precursors for inkjet printing of conductive copper patterns. The compounds with the general formula Cu[O2CCRR′(OC2H4)2OCH3]2 (R = R′ = H: 2a; R = H, R′ = Me: 2b; R = R′ = Me: 2c; R = H, R′ = Ph: 2d, R/R′ = O: 2e) show a high solubility in water and many organic solvents. By thermal decomposition the compounds yield pure copper as the only non-volatile product, as confirmed by X-ray powder diffraction and energy-dispersive X-ray spectroscopy. Depending on the substituents R and R′ the decomposition temperature varies between 175 and 220 °C. The mechanism of the thermal degradation was studied by thermogravimetry–mass spectrometry coupling experiments.For complex 2a, an aqueous 1.5 M solution (7.7 wt.% copper) exhibits rheological properties that are well-suited for inkjet printing. Thermal conversion of the as-printed structures under inert conditions yielded copper layers with only minor residues of carbon and oxygen. Electrical conductivities of 1.5 · 106 S·m− 1 on polyimide and 8.1 · 106 S·m− 1 on glass were found, which correspond to 2.6 and 14% of the bulk copper conductivity, respectively.