Gallium-nitride (GaN) developments continue to hit the headlines as two of Japan’s industrial heavyweights have unveiled significant innovations. Mitsubishi Heavy Industries (MHI) says it is the first company to directly bond silicon carbide (SiC) and GaN with silicon at room temperature. Meanwhile, Panasonic has created a transistor using GaN that has important implications for communications applications.
Why is room temperature bonding so desirable? The answer is twofold. First, a room-temperature process eliminates the risk of heat stress and strain on the device while simultaneously ensuring a reliable merging of the structural materials. The other advantage is the reduction in manufacturing time. Previous processes required both heating and cooling periods, which are now redundant. Room temperature, then, cuts production costs and increases production speed.
MHI’s bonding machine uses a technique that bonds atoms of various materials at room temperature by activating the materials with ion beam radiation in a vacuum. The machine can bond various materials. MHI also has been successful in the room-temperature bonding of SiC, GaN, and sapphire with silicon.
SiC is attracting a lot of attention currently from designers working on future power semiconductor devices. Sapphire can be used in the creation of high-frequency circuits when bonded with silicon to produce silicon on sapphire.
The coupling of GaN onto silicon substrate is at the heart of the Panasonic development. The company has produced a GaN-based transistor that has been integrated into a wireless transceiver capable of operating at 25 GHz. The power output of the transceiver at 25 GHz gives it a theoretical range of more than 80 km.
Panasonic believes the combination of GaN and a silicon substrate is suitable for mass production. It uses an unusual epitaxial structure that enhances the crystal quality of the structure, which has a positive effect on drain current performance, according to the company.
This wireless transceiver is well suited to high-capacity data transmission. Communication distances will certainly be extended, particularly as the GaN transistor outperforms more conventional gallium-arsenide (GaAs) transistors, though GaAs technology has served communication apps very well since its introduction back in the early 1980s.
So, GaN transistors look to have a promising future in millimeter-wave long-distance communication systems requiring high speed and high data capacity.