Printed optical electronics come into view

Researchers in the EU-funded CONTACT project have demonstrated that organic LCDs and other optical electronic devices can be precisely printed.

The Technical University of Ilmenau, a CONTACT partner, has shown that patterned glass plates can be used within the printing process.

In addition to being able to cheaply fabricate large numbers of everyday devices such as watch displays, the researchers predict further applications could include electronic paper, eyeglasses with embedded displays and smart clothing.

The researchers hope to follow this proof-of-principle by developing a gravure printing press. The press will be able to print hundreds of thousands of organic thin-film, transistor arrays precisely and efficiently.

The press is being created by Switzerland-based Schläefli Machines, another project partner. The company’s challenge is to perfect the machinery needed to correctly align the layers of materials needed to form arrays of organic TFTs and other circuit elements.

According to Alan Mosley, project coordinator, the most challenging problem the project team encountered was when they tried to lay down the first layer of a liquid crystal display over the TFT array they had already printed.

“What we found was that when we put down the first layer associated with the liquid crystal manufacture, it destroyed the TFT layer,” Mosley said.

“You have to use aggressive solvents, which attack organic materials.”

Project researchers at the Imperial College London found ways to modify the inks and other materials making up the TFT layer so that it was able to resist the solvents.

The result is a process for printing a TFT layer that is compatible with an LCD.

The group’s next challenge is to replace the current printing platform, Labratester 1, with the Labratester 2. Although both presses are capable of printing the tiny structures needed for optical electronics — 25 micron features with 25 micron spacing — Labratester 2 will be able to align sequential layers with 10 micron precision.

Mosley explained, the press will use optical cameras to detect alignment marks in order to register each layer precisely over the previous one.

Mosley expects that Labratester 2 will stimulate the entire organic electronics sector. The press is currently capable of printing only moderate numbers of devices at a time, but the advances that have gone into it can be transferred to faster machines.

ICT Results
http://cordis.europa.eu/ictresults