Currently, indium tin oxide (ITO) is almost universally the material of choice for building transparent electronics, because it is both electrically conductive, as well as optically transparent.
Demand for indium is on the increase continually, as its uses range from light-harvesting solar panels to touch-sensitive smartphone screens. Due to the scarcity of indium, this increase in demand means the price is also sharply increasing.
A research team at KAUST have found an alternative way to manufacture transparent transistors and other essential components for electronic circuitry. Their simple manufacturing technique does not use indium, but utilizes inexpensive and readily available materials.
Aluminum-doped zinc oxide (AZO) is one alternative. As a transparent material that is low cost, it shows promise for this type of application. The leader of the research, Professor Husam Alshareef from the KAUST Physical Science and Engineering Division, notes that AZO as an option that makes commercial sense, as the elements that make up this material are more readily available than indium. The drawback thus far has been that electronic devices made using ITO have shown superior performance to those manufactured using AZO.
Alshareef and his team used a high precision technology to overcome this limitation. The technology uses a process called atomic layer deposition where the circuitry is built up a single layer of atoms at a time. Unstable fumes of zinc and aluminum in the form of diethyl zinc and trimethyl aluminum were alternately introduced onto the transparent substrate. These fumes then first adhere to the surface in a single layer, after which they react to form AZO.
The circuit fabrication process is simplified when atomic layer deposition is used to grow all active layers. Circuit performance is significantly improved by controlling layer growth at the atomic scale.
Thin film transistors are key components in many electronic devices. These devices drive displays, act as active sensors and allow computers to do calculations when combined in great numbers. Alshareef’s method consists of using hafnium oxide (a transparent material) to sandwich between layers of zinc oxide. The resultant highly stable transistors are used to fabricate the transparent circuits
An additional advantage of this approach is that a temperature of only 160 degrees Celsius is required to form each layer. This temperature is so low that the transparent circuitry can be formed on rigid glass, as well as on flexible plastic substrates.
Full research has been published in the journal Advanced Materials.