Albert Folch, an assistant professor of bioengineering at the University of Washington, works with microfluidic masks constructed of hollow silicone grooves filled with colored dyes. The dye-filled channels make patterns on photoresist. Unlike metal masks, though, the microfluidic counterparts can be altered easily by merely changing the dye, Folch says. It takes only seconds to make a range of different shapes using even standard lithographic methods.

"Microfluidic photomasks are such a simple idea," the researcher insists, adding that they are much better able to print three-dimensional shapes than metal masks. The opacity of a dye can be easily regulated.

A darker blue dye will absorb more light than a translucent diluted dye, which will change pattern features. "The advantage of the technique is that it allows for an arbitrary number of gray-scales."

Folch describes creating resist patterns of varying sizes. One pattern uses five adjacent dye concentrations to make five lines of different heights. The ability to overcome the "all-or-nothing" limits of traditional photomasks may help chipmakers see more of one important color: green.