Nav: Home

Room-temperature bonded interface improves cooling of gallium nitride devices

March 11, 2020

A room-temperature bonding technique for integrating wide bandgap materials such as gallium nitride (GaN) with thermally-conducting materials such as diamond could boost the cooling effect on GaN devices and facilitate better performance through higher power levels, longer device lifetime, improved reliability and reduced manufacturing costs. The technique could have applications for wireless transmitters, radars, satellite equipment and other high-power and high-frequency electronic devices.

The technique, called surface-activated bonding, uses an ion source in a high vacuum environment to first clean the surfaces of the GaN and diamond, which activates the surfaces by creating dangling bonds. Introducing small amounts of silicon into the ion beams facilitates forming strong atomic bonds at room temperature, allowing the direct bonding of the GaN and single-crystal diamond that allows the fabrication of high-electron-mobility transistors (HEMTs).

The resulting interface layer from GaN to single-crystal diamond is just four nanometers thick, allowing heat dissipation up to two times more efficient than in the state-of-the-art GaN-on-diamond HEMTs by eliminating the low-quality diamond left over from nanocrystalline diamond growth. Diamond is currently integrated with GaN using crystalline growth techniques that produce a thicker interface layer and low-quality nanocrystalline diamond near the interface. Additionally, the new process can be done at room temperature using surface-activated bonding techniques, reducing the thermal stress applied to the devices.

"This technique allows us to place high thermal conductivity materials much closer to the active device regions in gallium nitride," said Samuel Graham, the Eugene C. Gwaltney, Jr. School Chair and Professor in Georgia Tech's George W. Woodruff School of Mechanical Engineering. "The performance allows us to maximize the performance for gallium nitride on diamond systems. This will allow engineers to custom design future semiconductors for better multifunctional operation."

The research, conducted in collaboration with scientists from Meisei University and Waseda University in Japan, was reported February 19 in the journal ACS Applied Materials and Interfaces. The work was supported by a multidisciplinary university research initiative (MURI) project from the U.S. Office of Naval Research (ONR).

For high-power electronic applications using materials such as GaN in miniaturized devices, heat dissipation can be a limiting factor in power densities imposed on the devices. By adding a layer of diamond, which conducts heat five times better than copper, engineers have tried to spread and dissipate the thermal energy.

However, when diamond films are grown on GaN, they must be seeded with nanocrystalline particles around 30 nanometers in diameter, and this layer of nanocrystalline diamond has low thermal conductivity - which adds resistance to the flow of heat into the bulk diamond film. In addition, the growth takes place at high temperatures, which can create stress-producing cracks in the resulting transistors.

"In the currently used growth technique, you don't really reach the high thermal conductivity properties of the microcrystalline diamond layer until you are a few microns away from the interface," Graham said. "The materials near the interface just don't have good thermal properties. This bonding technique allows us to start with ultra-high thermal conductivity diamond right at the interface."

By creating a thinner interface, the surface-activated bonding technique moves the thermal dissipation closer to the GaN heat source.

"Our bonding technique brings high thermal conductivity single crystal diamond closer to the hot spots in the GaN devices, which has the potential to reshape the way these devices are cooled," said Zhe Cheng, a recent Georgia Tech Ph.D. graduate who is the paper's first author. "And because the bonding takes place near room temperature, we can avoid thermal stresses that can damage the devices."

That reduction in thermal stress can be significant, going from as much as 900 megapascals (MPa) to less than 100 MPa with the room temperature technique. "This low stress bonding allows for thick layers of diamond to be integrated with the GaN and provides a method for diamond integration with other semiconductor materials," Graham said.

Beyond the GaN and diamond, the technique can be used with other semiconductors, such as gallium oxide, and other thermal conductors, such as silicon carbide. Graham said the technique has broad applications to bond electronic materials where thin interfacial layers are advantageous.

"This new pathway gives us the ability to mix and match materials," he said. "This can provide us with great electrical properties, but the clear advantage is a vastly superior thermal interface. We believe this will prove to be the best technology available so far for integrating wide bandgap materials with thermally-conducting substrates."

In future work, the researchers plan to study other ion sources and evaluate other materials that could be integrated using the technique.

"We have the ability to choose processing conditions as well as the substrate and semiconductor material to engineer heterogenous substrates for wide bandgap devices," Graham said. "That allows us to choose the materials and integrate them to maximize electrical, thermal and mechanical properties."
-end-
In addition to the researchers already mentioned, the paper included co-corresponding author Fengwen Mu from Meisei University and Waseda University in Japan, Luke Yates from Georgia Tech, and Tadatomo Suga from Meisei University.

This research was supported by the U.S. Office of Naval Research (ONR) through MURI Grant No. N00014-18-1-2429. Any findings, conclusions, and recommendations are those of the authors and not necessarily of the Office of Naval Research.

CITATION: Zhe Cheng, Fengwen Mu, Luke Yates, Tadatomo Suga and Samuel Graham, "Interfacial Thermal Conductance across Room-Temperature-Bonded GaN/Diamond Interfaces for GaN-on-Diamond Devices," (ACS Appl. Mater. Interfaces, 2020, 12, 8376?8384). https://doi.org/10.1021/acsami.9b16959

Georgia Institute of Technology

Related Diamond Articles:

The IKBFU scientists created the first diamond x-ray micro lens
A diamond is a unique and expensive material. But it is almost indestructible which makes the lens made of it more economically profitable than metallic or polymeric ones in the long run.
Stanford research maps a faster, easier way to build diamond
With the right amount of pressure and surprisingly little heat, a substance found in fossil fuels can transform into pure diamond.
Bending diamond at the nanoscale
A team of Australian scientists has discovered diamond can be bent and deformed, at the nanoscale at least.
A tech jewel: Converting graphene into diamond film
Can two layers of the ''king of the wonder materials,'' i.e. graphene, be linked and converted to the thinnest diamond-like material, the ''king of the crystals''?
Researchers teleport information within a diamond
Researchers from the Yokohama National University have teleported quantum information securely within the confines of a diamond.
News from the diamond nursery
Unlike flawless gems, fibrous diamonds often contain small saline inclusions.
Nanoscale thermometers from diamond sparkles
The development of a novel, non-invasive technique that uses quantum light to measure temperature at the nanoscale will have immediate applications for both industry and fundamental scientific research, scientists say.
Unprecedented insight into two-dimensional magnets using diamond quantum sensors
For the first time, physicists at the University of Basel have succeeded in measuring the magnetic properties of atomically thin van der Waals materials on the nanoscale.
Diamond doves do not optimize their movements for flexible perches
The diamond dove may preferentially select large, stiff materials for takeoff and landing sites, according to a study published on July 25 in the open-access journal PLOS ONE.
Tunable diamond string may hold key to quantum memory
Researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the University of Cambridge engineered diamond strings that can be tuned to quiet a qubit's environment and improve memory from tens to several hundred nanoseconds, enough time to do many operations on a quantum chip.
More Diamond News and Diamond Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Climate Mindset
In the past few months, human beings have come together to fight a global threat. This hour, TED speakers explore how our response can be the catalyst to fight another global crisis: climate change. Guests include political strategist Tom Rivett-Carnac, diplomat Christiana Figueres, climate justice activist Xiye Bastida, and writer, illustrator, and artist Oliver Jeffers.
Now Playing: Science for the People

#562 Superbug to Bedside
By now we're all good and scared about antibiotic resistance, one of the many things coming to get us all. But there's good news, sort of. News antibiotics are coming out! How do they get tested? What does that kind of a trial look like and how does it happen? Host Bethany Brookeshire talks with Matt McCarthy, author of "Superbugs: The Race to Stop an Epidemic", about the ins and outs of testing a new antibiotic in the hospital.
Now Playing: Radiolab

Speedy Beet
There are few musical moments more well-worn than the first four notes of Beethoven's Fifth Symphony. But in this short, we find out that Beethoven might have made a last-ditch effort to keep his music from ever feeling familiar, to keep pushing his listeners to a kind of psychological limit. Big thanks to our Brooklyn Philharmonic musicians: Deborah Buck and Suzy Perelman on violin, Arash Amini on cello, and Ah Ling Neu on viola. And check out The First Four Notes, Matthew Guerrieri's book on Beethoven's Fifth. Support Radiolab today at Radiolab.org/donate.