Nanostructured gate dielectric could enable large flexible displays

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According to scientists from Georgia Tech, a nanostructured gate dielectric may solve a significant obstacle to wider use of organic semiconductors for thin-film transistors. A potential application for the technology could be in very large flexible displays that could be rolled up when not in use.

The structure – a fluoropolymer layer, followed by a nanolaminate made from two metal oxide materials – not only serves as gate dielectric, but also protects the organic semiconductor from damage. A further benefit is said to be greater stability.

“We have now proven … that organic circuits can be as stable as devices produced with conventional inorganic technologies,” said Professor Bernard Kippelen. “This could be the tipping point for organic thin-film transistors, addressing long-standing concerns about the stability of organic-based printable devices.”

A novel aspect of the Georgia Tech development is the use of two components in the dielectric layer. “When we first developed this architecture, this metal oxide layer was aluminum oxide, which is susceptible to damage from humidity,” said researcher Canek Fuentes-Hernandez. “Working in collaboration with Professor Samuel Graham, we developed complex nanolaminate barriers which could be produced at temperatures lower than 110°C and that when used as gate dielectric, enabled transistors to sustain being immersed in water near its boiling point.”

The dielectric architecture features alternating layers of aluminum oxide and hafnium oxide – five layers of one, then five layers of the other, repeated 30 times on top of the fluoropolymer. The resulting nanolaminate is about 50nm thick and said to be ‘virtually immune’ to the effects of humidity.

Fuentes-Hernandez noted: “The performance of these transistors remained virtually unchanged, even when we operated them for hundreds of hours and at 75°C. This was by far the most stable organic-based transistor we had ever fabricated.”

For the laboratory demonstration, the researchers used a glass substrate, but many other flexible materials – including polymers and even paper – could also be used.

The team says an obvious application for its development is for transistors that control pixels in OLEDs. The technique could also allow development of inexpensive paper-based devices, such as smart tickets, that would use antennas, displays and memory fabricated on paper through low-cost processes.