Using this approach, Rogers and his colleagues have shown that they can print lines of a material 700 nanometers wide or individual dots just 250 nanometers in diameter.
In addition to the size of the droplets, the spatial accuracy is also improved, says Rogers. He and his team discovered quite serendipitously that the field used to create the droplet also helps guide the charged droplet toward the target substrate. “That was kind of a bonus,” Rogers says.
Electrohydrodynamic printers have been used in the past, says Howard Taub, associate director of HP Labs, in Palo Alto, CA. The novelty here is the high resolution, he says.
But, says Taub, what these new e-jets make up for in resolution they lack in speed. The high voltages required to generate the fields can be difficult to pulse in order to print quickly. Regular printers can eject droplets on the order of between 10,000 and 100,000 times a second. Rogers’s e-jets, on the other hand, operate at around 1,000 times a second.
One solution is to use arrays of inkjet heads, says Taub. But this can lead to further problems, he says: “The droplets are going to interact with each other because they are charged. So you’d have to keep them spaced out.”
Rogers says that his group is working on the speed issue. He and his colleagues have already shown that nozzles can be placed as close as 250 micrometers without droplets interacting. They are now working with several manufacturers to commercialize the technology.