15 December 2017
AFRL uses boron nitride to demo growth and lift-off of GaN for strainable RF devices
The Air Force Research Laboratory (AFRL) says it has discovered a new way to grow and transfer gallium nitride (GaN), laying the groundwork for future fifth-generation, high-speed, agile communication systems (Glavin et al, ‘Flexible GaN for High-Performance, Strainable Radio Frequency Devices’, Advanced Materials (14 December 2017); DOI: 10.1002/adma.201770338).
“We demonstrated the ability to grow and place the material on a flexible substrate, enabling the potential to power wearable devices or electronic devices that are not necessarily flat,” says Nicholas Glavin, a research scientist at the AFRL Materials and Manufacturing Directorate. “We are the first group ever to demonstrate a flexible RF (radio frequency) transistor device based on gallium nitride that actually performs under strain and is flexible,” he claims.
Although gallium arsenide is often the material of choice for wireless devices currently, it is limited in its ability to transmit high-frequency signals at high power, which can cause data degradation or slow speeds of transfer at high range. In contrast, GaN has an exceptional ability to transmit large amounts of information at a high frequency with high power, but it has been limited in application due to the high cost of material manufacturing, which typically requires a rigid substrate such as sapphire and precise thermal and chemical stability. Also, once grown on a substrate, GaN made this way can only be used in flat, planar platforms, unable to withstand bending or strain.
AFRL’s new method of GaN production takes advantage of the physical properties of boron nitride. The GaN is grown on the boron nitride and then, due to weak chemical bonds between the boron nitride and the growing surface, they can then lift and transfer the apparatus to another substrate, enabling communication capability on unique platforms and devices.
“It’s been a big DoD [Department of Defense] priority to further develop this material. We are the first to demonstrate a flexible RF transistor device using gallium nitride that maintains high-quality performance under strain using the transfer method,” claims Dr Donald Dorsey, the lead for the Agile Radio Frequency Electronic Materials and Processes Team. “We now have the potential to create high-frequency transmitters for high-power communications and radar that use gallium nitride in a more compact and versatile form.”
The ability to transfer the GaN to a flexible or other arbitrary substrate has tremendous value for the Air Force as communication needs continue to grow and expand at a rapid rate.
“There are two primary applications we see this research directly benefitting the Air Force,” says Glavin. “The first is in wearable systems - as we collect more information on our operators and develop more sensor technologies, we need to be able to take that information and communicate it for action. A flexible transmitter based on GaN can make this happen more efficiently,” he adds. “Another area that will benefit is flexible and conformal radar technology. Typical radar systems are big and bulky, but using this technology we can create systems that can be more easily integrated into dynamic environments.”
Another benefit is power amplification directly on antenna systems, says Dr Michael Snure, a senior physicist at the AFRL Sensors Directorate. “If you have a flexible power amplifier and can get it as close as possible to your radar antenna, you can improve performance simply by removing the distance a signal has to travel,” he adds. “Flexible GaN gets you the ability to place the amplifier up against the antenna on the same platform and improve performance and transmission.”
“We performed the demo state and are now focusing on material integration,” says Glavin. However, although research continues to optimize the ability for the AFRL-developed GaN to integrate with diverse material surfaces and to find ways to improve performance and the transfer process, the team is already in the process of obtaining patents for both the material growth process and the use of GaN in flexible RF devices.