GaN transistor

Defense Advanced Research Projects Agency (DARPA) scientists have completed demonstrations of the first-ever gallium nitride (GaN) on-diamond high electron mobility transistor (HEMT), as part of the near junction thermal transport (NJTT) programme.

Substantially lower junction temperatures were displayed by the transistor when compared with the other commercially available power amplifiers (PA) during early testing.

The enhanced thermal properties of new GaN transistor eventually improves performance of a wide range of military radio frequency (RF) systems, including radars and communication systems, as well as electronic warfare systems.

DARPA programme manager Avram Bar-Cohen said the GaN-on-diamond HEMTs may advance a new generation of RF PAs that are three times smaller than the existing GaN amplifiers, leading to development of RF systems with better size, weight and power characteristics.

"Alternatively, PAs like these would be able to generate three times as much output power, leading to a stronger signal for communication systems or longer range radar," Cohen said.

"Providing a high-conductivity substrate in intimate contact with the GaN gets us unsurpassed heat tolerance and dissipation capability."

Operational performance of the existing GaN monolithic microwave integrated circuits (MIMIC) PAs in the military RF systems is restricted by high-thermal resistance of the region within 100µm of the electronic junction, also called the near junction region.

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The GaN was removed from the circuits’ silicon-based growth substrate by TriQuint Semiconductor through an epitaxial transfer method, and placed closely with a synthetically grown, high thermal conductivity, diamond substrate.

"Providing a high-conductivity substrate in intimate contact with the GaN gets us unsurpassed heat tolerance and dissipation capability," Cohen added.

An initiative of DARPA’s Thermal Management Technologies (TMT) programme, NJTT is expected to offer technologies for improved device-level thermal management for GaN PAs, and several electronic and optical systems of interest to the Department of Defense (DoD).

Image: The GaN-on-diamond transistor features improved thermal properties compared to commercial power amplifiers. Photo: courtesy of DARPA.

Defence Technology