The US Air Force Research Laboratory (AFRL) has announced that it has discovered a new method of growing and transferring gallium nitride (GaN) that lays the foundation for future fifth-generation, high-speed, flexible communications systems.
Nicholas Glavin, a scientist in AFRL's Materials and Manufacturing Division, said: "We have demonstrated the ability to grow and place materials on flexible substrates, opening up the potential for powering wearable devices or electronic devices. We are the first company ever to demonstrate a flexible RF (radio frequency) transistor device based on gallium nitride that is actually somewhat ductile and flexible."

A new approach to GaN manufacturing

Gallium Arsenide (GaAs) is often the material of choice for infinite devices, but the limited ability of GaAs to transmit high frequency signals at high power makes it suffer from delays or low data transfer rates when transmitting high frequency data. In contrast, GaN has a superior ability to transmit large amounts of data information at high power and high frequency, but the high cost of manufacturing the material, which usually requires a rigid substrate such as sapphire, precise thermal stability and chemical stability, limits its application. In addition, GaN grown on substrates using this method can only be used in flat planes and cannot be bent or stretched.

AFRL's new GaN production method takes advantage of the physical properties of boron nitride. GaN is grown on boron nitride and then, using a weak chemical bond between the boron nitride and gallium nitride growth surfaces, allows the gallium nitride to be transferred to another substrate, enabling communication capabilities on a unique platform and device.

Significance of the results

We see two major applications where this research directly benefits the Air Force," Glavin said. One is wearable systems. As we collect more information through wearable devices such as warfighters carrying personnel, or as we develop more sensor technology, we need to access that information and inform action. GaN-based flexible transmitters can perform these operations more effectively. Secondly, there is flexible conformal radar technology. Typical radar systems are bulky, but using this technology we can create systems that are easier to integrate into dynamic environments."

Another benefit is the power amplification directly on the antenna system. With a flexible power amplifier, it is possible to get as close as possible to the radar antenna and simply eliminate the distance the signal has to travel to improve performance. The flexible GaN enables the amplifier to be placed on the same platform as the antenna, improving performance and transmission efficiency.

Flexible GaN with great potential

Further development of GaN materials is a top priority for the Department of Defense," said Dr. Donald Dorsey, head of the AFRL Flexible RF Electronics Materials and Processes team. We are the first team to demonstrate GaN flexible RF transistor devices that can maintain high performance under stretching. We are well positioned to develop more compact, versatile GaN HF transmitters for high power communications and radar."

With the growing and rapidly expanding demand for communications, the ability to transfer GaN to flexible or other arbitrary substrates is of great value to the Air Force.

Future work

Glavin said, "We are working on materials integration and will continue to optimize the ability to integrate the GaN developed by AFRL with a variety of material surfaces and will look for ways to enhance performance and transfer processes. The team has filed patents for both the material growth process and the use of GaN for RF devices."