New See-Through Circuitry To Power Smart Windows

Jeddah: Scientists have found a way to make transparent
transistors and other essential components of electronic circuitry, an advance
that may lead to displays on car windscreens, transparent TV sets and smart
windows.

Indium tin oxide (ITO) is the current material of choice
for electronics because it combines optical transparency with electrical
conductivity.

Its use ranges from touch-sensitive smartphone screens to
light-harvesting solar panels. Indium is in short supply, 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), researchers said. The
elements that make up this material are more abundant than indium, making AZO a
commercially sensible option, said Professor Husam Alshareef from the King
Abdullah University of Science and Technology (KAUST) in Saudi Arabia.

However, electronic devices made using AZO have
traditionally shown inferior performance to devices made using ITO, said
Alshareef, who led the research. To overcome this limitation, researchers used
a high-precision technology called atomic layer deposition, a process in which
the circuitry is built up a single layer of atoms at a time.

Volatile vapours of aluminium and zinc in the form of
trimethyl aluminium and diethyl zinc were alternately introduced onto the
transparent substrate, where they 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 said.

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 that was sandwiched between layers of zinc oxide 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 Zhenwei Wang, PhD
student at KAUST.

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

PTI