The University of Bristol is leading an important new five-year project to develop technology for the next generation of wireless systems, 6G.

The £4.3 million grant from the Engineering and Physical Sciences Research Council (EPSRC) is to work on Gallium Nitride (GaN)-on-Diamond microwave technology that will be used for future high power radio frequency and microwave communications, space and defence systems.

This will form that basis of 5G and 6G mobile phone networks and much more comprehensive radar systems. Bristol will work with four other universities (Cardiff, Glasgow, Cambridge and Birmingham) and industry partners during this five-year project.

“Global demand for high power microwave electronic devices that can deliver power densities well exceeding current technology is increasing,” says Professor Martin Kuball, from the School of Physics at Bristol who is leading the project. “In particular GaN-based high electron mobility transistors (HEMTs) are a key enabling technology for high-efficiency military and civilian microwave systems, and increasingly for renewable energy plants.”

100 gigabits per second needed

5G systems are currently being demonstrated running at over 10Gbit/s in Bristol and Sweden and will start rolling out commercially in 2018. Future 6G systems for 2028 will require even higher data rates, targeting 100Gbit/s. Current microwave devices do not have the performance needed, so the new project is to develop new GaN-on-Diamond HEMTs and monolithic microwave integrated circuits (MMICs).

“The energy flows in these devices can be as high as the heat flux on the surface of the sun”


This is a major challenge as the energy flows in these devices can be as high as the heat flux on the surface of the sun, and the diamond is the only material which can handle them. “To enable our vision to become reality, we will develop new diamond growth approaches that maximise diamond thermal conductivity close to the active GaN device area,” explains Professor Kuball. In current GaN-on-Diamond devices a thin dielectric layer is required on the GaN surface to enable seeding and successful deposition of diamond onto the GaN. Unfortunately, most of the thermal barrier in these devices then exists at this GaN-dielectric-diamond interface, which has much poorer thermal conductivity than desired.

“Any reduction in this thermal resistance, either by removing the need for a dielectric seeding layer for diamond growth, or by optimising the grain structure of the diamond near the seeding, would be of huge benefit. Novel diamond growth will be combined with innovative micro-fluidics using phase-change materials, a dramatically more powerful approach than conventional micro-fluidics, to further aid heat extraction,” he adds.

The outcome will be devices able to support five times the RF (Radio Frequency) power of today’s GaN-on-silicon carbide HEMTs. This performance could be used for higher bit rates, smaller size systems or longer battery life. Less need for cooling and increased reliability will also provide major cost savings at the system level.

There’s a video of how some of today’s high performance 5G systems work at the Communication Systems & Networks Research Group website

Nick Flaherty