Ober, who developed the photoresist and solvent, says Malliaras has “taken this process and enhanced it to apply to the production of very complex organic transistors, sensors, solar cells, and ring oscillators” (devices that convert direct current into alternating current). Orthogonal is currently showing these four prototypes to potential customers. So far, the process has proven compatible with all the organic semiconducting materials the group has tested. Ober says the solvents are also environmentally benign and easy to work with. While the new solvents may cost more than those used to make silicon electronics, the price of the photoresist should be equivalent. Overall, the process should be cheaper than making silicon electronics.
The performance of devices made using orthogonal lithography is equivalent to organic devices made using other techniques, says Orthogonal CTO John de Franco. The company’s first products, which it hopes to sell in about a year, will be materials for making organic light-emitting diodes. Orthogonal has built prototype pixels using the technique. “Their efficiency is comparable to standard devices, and we’re currently looking at lifetimes,” which can be a problem with organic display materials, says de Franco.
Ober expects orthogonal lithography to make more-advanced organic electronics possible, with layered devices capable of performing more complex operations. When multilayer organic devices are made using printing techniques such as ink-jet printing, each layer disturbs the previous one, he says. The devices are made from inks that consist of a semiconductor in a solvent. But the solvent, which is required to print successive layers, can interact with the semiconductors that have already been printed, with serious consequences for performance. This intermixing between layers isn’t a problem when making multilayer devices using orthogonal lithography because the fluorinated solvents interact only with the photoresist, and not with the organic semiconductor. “Each layer can be placed down without intermixing,” says Ober.
Zhenan Bao, an associate professor of chemical engineering at Stanford University, says the company’s approach is unique. Other groups have focused on developing cheaper manufacturing technologies–if the initial investment in equipment is not factored in, ink-jet printing and other techniques are cheaper. But Bao expects that Orthogonal could get a foothold in the display market. “These are products that are not necessarily going to be cheap and disposable, so lithography may be affordable,” she says. “And using existing infrastructure could be an advantage, especially for display companies.”