Jet-printed Phase-change Etch Masks

The challenge for jet-print patterned TFT devices is achieving sufficient precision and reliability to fabricate electronic circuits having the desired feature size and performance. This section discusses the feasibility of using phase-change etch masks patterned by jet printing, in place of conventional photolithography. 

The use of inkjetted liquids to directly write etch masks is a practical alternative to printed toner although jet printing also possesses inherent complexities. For example, when a resist that is dissolved in a solvent is put on a surface, the droplet size is largely determined by its wetting properties. Typically, small wetting angles are required to obtain good adhesion to a surface but this condition enables the liq- 

The use of a phase-change media circumvents many of these problems. A material slightly above its liquid/solid-phase transition temperature may be ejected from a jet-printing nozzle the droplet solidifies quickly upon contact with a cooler surface. The feature size will then depend more on the cooling rate and less on the material s wetting properties, because a frozen droplet cannot spread. In this situation, the substrate temperature controls the printed feature size for materials having excellent wetting properties. 

The phenomenon has been studied by Gao and Sonin [16] and it has been shown that the cross-sectional area and apparent contact angle of a printed bead is a function of the substrate temperature and the print-scan velocity. A quantitative analysis of jet-printed phase change materials was reported by Schiaffino and Sonin [17] for isothermal conditions. The results showed that the contact angles for the printed drops could be varied as a function of the substrate temperature. By adjusting the substrate temperature and the scanning speed, the feature size and print quality can be adjusted without having to modify the substrate surface energy. 

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