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Unlocking Future Communications



The next generation of communications systems, including ultrafast 5G wireless networks, will require devices that can operate at millimetre-wave bands with minimal cost and maximum efficiency.

Now, Professor Ng Geok Ing and his research team at Nanyang Technological University’s School of Electrical and Electronic Engineering (EEE) have partnered others to develop 40 nanometre gate length gallium nitride high- electron-mobility transistors on silicon substrates with the highest cut-off frequency ever recorded, at 250 gigahertz (GHz). Their invention has potential applications in high-frequency and high-power performance devices.

The researchers used metal-organic chemical vapour deposition to grow the transistor’s epitaxial structure on silicon with high-resistivity. High-resistance substrates help to prevent energy losses from induced current flows in high-frequency applications.

Its ohmic source and drain contacts were made with annealed titanium, aluminium, nickel and gold, while the rectangular gate was constructed using nickel and gold. Further metalisation for the interconnects and probe pads was carried out with titanium and gold.

While other reported III-nitride devices on silicon substrates have achieved similar drain currents, the researchers said that their device design has the edge on other devices in two ways: it has a higher mobility and thinner total barrier thickness.

Their creation’s performance also compares well with gallium-nitride high-electron mobility transistors produced on silicon carbide substrates, which have smaller diameters and are much more expensive.

While their transistor has a relatively low maximum oscillation of 60 GHz, the researchers noted that this could be improved through the use of a T-shaped gate structure. They added that reducing the transistor’s gate length to 20 nanometres and adopting a self- aligned process in it could improve its performance.

Fig. 1 Schematic diagram and TEM image (gate region) of a 40 nanometres gate length InAlN/GaN on silicon substrate

Fig. 2 Comparison of the cut-off frequencies (fT) of GaN HEMTs on Si in this work with other reported GaN HEMTs on silicon substrates and GaN HEMTs on silicon carbide substrates. The inset shows the Lg dependence of fT• Lg product

By Professor Ng Geok Ing​

Click here to find out more.

Published on: 23-April-2018​​​​
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