Variation in the line stability of an inkjet printed optical waveguide-applicable material

Inkjet printing of functional materials is seen as an attractive route to large scale fabrication of optical waveguides due to the low cost and flexibility of this deposition method. Inkjet printing has been applied to many manufacturing processes, including deposition of functional polymers for use in light emitting devices (LEDs) and is seen as an attractive low-cost route to the manufacture of printed circuit boards (PCBs). Optical waveguides for PCBs are expected to have core dimensions of typically 50-100 mum with a square cross-section and will be surrounded by a cladding material of lower refractive index. The direct printing of high aspect-ratio core structures is a challenging proposition. For example, the choice and formulation of the jettable material is crucial as material properties such as viscosity and surface tension will affect how well the material is ink-jetted. Furthermore, the interaction of the ink-jetted material with the substrate is fundamental in determining the wetting behaviour and subsequently the aspect ratio of the structure and its stability. In this paper an initial investigation of the ink jet printing of a UV-curable waveguide-applicable material is presented and its suitability for optical waveguide fabrication assessed. The behaviour of ink-jetted lines of core material mixed with one of two solvents was studied, together with the influence of substrate wettability. It was found that droplets deposited onto cladding material surfaces spread substantially, leading to broad, shallow structures, while using a low energy, hydrophobic surface led to significantly reduced spreading. The influence of substrate temperature on the droplet spread was also investigated.