Inkjet printing of thin metal-oxide structures from sol-gel precursor inks

Inkjet printing is a deposition technique capable of direct patterning of functional materials on selected substrates. We demonstrate the inkjet printing of tantalum-oxide-based dielectric structures on conductive indium-tin-oxide-coated glass. The viscosity of the ink consisting of Ta-, Al-, and Si- alkoxide precursors dissolved in 2-methoxyethanol (2MOE) could be adjusted by adding highly viscous glycerol (GLY) or 1,3-propanediol (PD). Inks with optimized physical properties showed excellent jetting performance and could be printed even after several months. However, the ink design based merely on adjusting the physical properties proved to be insufficient as the drying of such inks resulted in an irregular surface morphology. We show that the adjustment of the ink's solvent composition with respect to the volatility of a particular solvent improves the uniformity of dried deposits. The optimized ink formulation with the 65:25:10=2MOE:GLY:PD solvent ratio enabled printing of flat and uniform thin-film capacitors with the performance comparable to the spin-coated films of the same composition.