Indium tin oxide (ITO) is the current material of choice because it combines optical transparency with electrical conductivity. 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 aluminium-doped zinc oxide (AZO).
“The elements that make up this material are more abundant than indium, making AZO a commercially sensible option,” said Professor Husam Alshareef from the KAUST Physical Science and Engineering Division. “However, electronic devices made using AZO have traditionally shown inferior performance to devices made using ITO.”
To overcome this, Prof Alshareef and his research team used atomic layer deposition (ALD). Volatile vapours of aluminium and zinc in the form of trimethyl aluminum and diethyl zinc are alternately introduced onto the transparent substrate, where they adhere to the surface in a single layer before reacting to form AZO.
“Using ALD to grow all active layers simplifies the circuit fabrication process and significantly improves circuit performance by controlling layer growth at the atomic scale,” Prof Alshareef explained.
Prof Alshareef used hafnium oxide sandwiched between layers of zinc oxide to form the transistors in the transparent circuits.
Another advantage of the approach is that ALD only requires a temperature of 160°C to form each layer, which is low enough for the transparent circuitry to be created on flexible plastic substrates as well as glass.
