‘Greener,’ low-cost transistor heralds advance in flexible electronics

September 29, 2014

This transparent transistor, which functions even when wrapped around a thin pen, could help make flexible electronics widely accessible (credit: American Chemical Society)

As LG demonstrated this summer with its new 18-inch partially flexible curved screen, the next generation of roll-up displays may be tantalizingly close.

Now UCLA and Yonsei University researchers have taken the next step, with an inexpensive, simple new way to make transparent, flexible transistors that could help bring roll-up smartphones with see-through displays and other bendable gadgets to consumers in just a few years, as they reported in the journal ACS Nano.

Transistors are traditionally made in a multi-step photolithography process, using light to print a pattern onto a glass or wafer.

This approach is costly and involves a number of toxic substances. Finding a greener, less-expensive alternative has been a challenge. New processing techniques using metal oxide semiconductors have recently attracted attention, but the resulting devices are lacking in flexibility or other essential traits.

Image of wafer-scale transparent oxide electronics using direct light pattern (DLP) integration of metal oxide films for large-scale circuit integration (credit: You Seung Rim et al./ACS Nano)

So the researchers developed inks that create patterns on ultrathin, transparent devices when exposed to light. This light sensitivity precludes the need for harsh substances or high temperatures.

“The main application of our transistors is for next-generation displays, like OLED or LCD displays,” said Yang Yang of UCLA’S department of Materials Science and Engineering. Our transistors are designed for simple manufacturing. We believe this is an important step toward making flexible electronics widely accessible.”

Abstract of Direct Light Pattern Integration of Low-Temperature Solution-Processed All-Oxide Flexible Electronics

The rise of solution-processed electronics, together with their processing methods and materials, provides unique opportunities to achieve low-cost and low-temperature roll-to-roll printing of non-Si-based devices. Here, we demonstrate a wafer-scale direct light-patterned, fully transparent, all-solution-processed, and layer-by-layer-integrated electronic device. The deep ultraviolet irradiation of specially designed metal oxide gel films can generate fine-patterned shapes of ∼3 μm, which easily manifest their intrinsic properties at low-temperature annealing. This direct light patterning can be easily applied to the 4 in. wafer scale and diverse pattern shapes and provides feasibility for integrated circuit applications through the penetration of the deep ultraviolet range on the quartz mask. With this approach, we successfully fabricate all-oxide-based high-performance transparent thin-film transistors on flexible polymer substrates.