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Fujitsu successfully triples output power of gallium nitride transistors

Fujitsu and Fujitsu Laboratories have developed a crystal structure that increases current and voltage in gallium-nitride (GaN) high electron mobility transistors (HEMT), effectively tripling the output power of transistors used for transmitters in the microwave band.

The GaN HEMT technology can serve as a power amplifier for equipment such as weather radar and it is expected that the observation range of the radar could be expanded by 2.3 times, enabling early detection of cumulonimbus clouds that can develop into torrential rainstorms.

Fujitsu Laboratories has been conducting research on GaN HEMTs since the early 2000's, and provides the aluminum-gallium nitride (AlGaN) HEMTs used in a variety of areas. Recently, Fujitsu Laboratories has been conducting research on indium-aluminum-gallium nitride (InAlGaN) HEMTs as a new generation GaN HEMT technology, which enables high current operation as high-density electrons become available.

To expand the observation range of equipment like radar, it is essential to increase the output power of the transistors used in power amplifiers. With conventional technology, applying a high voltage can easily damage the crystals that compose a transistor, making it technically difficult to increase current and voltage simultaneously, which is required to achieve high-output power GaN HEMTs.

The crystal structure developed improves operating voltage by dispersing the applied voltage to the transistor, preventing crystal damage. This technology has enabled Fujitsu to successfully achieve the highest power density at 19.9 watts per millimetre of gate width for GaN HEMT employing an indium-aluminium-gallium nitride (InAlGaN) barrier layer.

By inserting the newly developed high-resistant AlGaN spacer layer, the voltage within the transistor can be dispersed across both the electron supply layer and the AlGaN spacer layer. By mitigating the concentration of voltage, the kinetic energy increase of the electrons within the crystal is suppressed and damage to the electron supply layer prevented, leading to an improved operating voltage of up to 100 volts. This operation voltage corresponds to over 300,000 volts if the distance between the source electrode and gate electrode is one centimetre.

Furthermore, by applying the single-crystal diamond substrate bonding technology Fujitsu developed in 2017, the heat generation within the transistor can be efficiently dissipated through diamond substrate, enabling stable operations.

The research was partially supported by Innovative Science and Technology Initiative for Security, established by the Acquisition, Technology & Logistics Agency (ATLA) of the Japanese Ministry of Defense.

Neil Tyler

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