POWER DEVICES GaN-on-Diamond for power devices

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Gallium nitride (GaN) is a material that can be used in the production of semiconductor power devices, LEDs, and RF components. It is a ‘hot’ material that can be integrated with other materials to boost its performance.

One of these materials is diamond, and GaN-on-diamond offers key parameters that are a boon for electronics and make the material particularly attractive for high power RF applications such as sensitive radar applications. These are high thermal conductivity, high electrical resistivity, and both device- and system-level form factor.

Replacing MOSFETs in power electronics applications

The power electronics industry has seen silicon MOSFETs hit theoretical performance limits, so now is the time to move to a new element. Enter gallium nitride (GaN)—a wide bandgap, high electron mobility conductor that has demonstrated itself as being capable of meeting the performance requirements of new applications. High-electron-mobility transistor (HEMT) devices that are based on GaN are a potential successor to MOSFETs due to its superior electrical characteristics.

As a wide bandgap material, GaN’s forbidden band—the energy required for one electron to pass from the valence band to the conduction band—is a lot wider than the one in silicon. Due to this high required energy, the materials that are required for GaN to block a certain voltage, in contrast to silicon, are as many as 10 times thinner. This means that GaN can be used to create devices at a much smaller size. GaN can also operate at switching frequencies that are 10 times higher than silicon, resulting in low switching losses and less heat generation.

Boosting GaN’s performance with diamond

GaN-based HEMTs currently have their maximum output power limited by the high temperature of the channel substrate, degrading system performance and reliability.

However, new technique developed by a team from Georgia Tech, Meisei University, and Waseda University enables the placing of highly thermal conductive materials much closer to the regions of the active devices in GaN. This maximizes GaN’s performance for higher power operations.

Diamond is currently the material with the highest thermal conductivity due to its covalent bonding and low phonon scattering, and via its integration with GaN, it can dissipate heat generated near the channel. This means that devices using GaN integrated with diamond, even better thermal conductivity and electrical resistivity can be realized, allowing it to reduce device operating temperatures and improve longevity. These are ideal features for a range of power electronics applications like 5G base stations and satellite communications.

“During the HEMT device working, a large voltage drop near the gate induces localized Joule-heating. The heating area is located within tens of nanometers, which results in super-high local heat flux. The local heat flux value of GaN-based HEMTs could reach more than ten times larger than that of the sun surface. Proper heat spreading technique, such as putting diamond as close as possible to the hot-spots, could decrease the channel temperature effectively, facilitating the device stability and lifetime,” said Zhe Cheng, a recent Georgia Tech Ph.D. graduate who is the paper’s first author.

The technique used by the researchers involved the direct growth of diamond on GaN. The combination of the thermal resistance of the materials and the interfaces played a core role in heat flow management, especially for high-frequency applications for switching power supplies.

For over a decade now, GaN-on-diamond has been in development, but it is expected to be launched commercially within the next few years. The team’s research was published in ACS Publications earlier this year.

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