New method clears way to creating transparent transistors

"Our transistor properties are the best reported so far for fully transparent transistors using AZO contacts."Zhenwei Wang, KAUST

High-performance electronic circuits made entirely from transparent materials could have countless applications, from head-up displays on car windscreens to transparent TV sets and smart windows in homes and offices. Researchers at the King Abdullah University of Science & Technology (KAUST) in Saudi Arabia have now found a way to make transparent transistors and other essential components of electronic circuitry using inexpensive and readily available materials with a simple fabrication technique. They report this work in a paper in Advanced Materials.

Indium tin oxide (ITO) is the current material of choice for transparent electronics, with uses ranging from touch-sensitive smartphone screens to light-harvesting solar panels. Indium is in short supply, however, and as demand increases for ITO-containing devices, so does the price of indium.

One promising low-cost ITO alternative is a transparent material known as aluminum-doped zinc oxide (AZO). "The elements that make up this material are more abundant than indium, making AZO a commercially sensible option," said Husam Alshareef, a professor in the KAUST Physical Science and Engineering Division, who led the research. "However, electronic devices made using AZO have traditionally shown inferior performance to devices made using ITO."

To overcome this limitation, Alshareef and his research team took advantage of a high-precision technique called atomic layer deposition, which can build up circuits a single layer of atoms at a time. Using this technique, the researchers applied volatile vapors of aluminum and zinc in the form of trimethyl aluminum and diethyl zinc to a transparent substrate, where the aluminum and zinc adhere to the surface in a single layer before reacting in situ to form AZO.

"Using atomic layer deposition to grow all active layers simplifies the circuit fabrication process and significantly improves circuit performance by controlling layer growth at the atomic scale," Alshareef explained.

For many electronic devices, the key component is the thin-film transistor. When combined in great numbers, these devices allow computers to do calculations, drive displays and act as active sensors. Alshareef used a transparent material called hafnium oxide, sandwiched between layers of AZO, to form the highly-stable transistors used to fabricate the transparent circuits.

"Our transistor properties are the best reported so far for fully transparent transistors using AZO contacts," said PhD student Zhenwei Wang, who carried out much of the experimental work.

Another advantage of Alshareef's approach is that atomic layer deposition only requires a temperature of 160°C to form each layer. This is low enough for the transparent circuitry to be formed on flexible plastic substrates, as well as on rigid glass.

This story is adapted from material from KAUST, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.