Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Silver-Diamond Composite Cools Powerful Electronics

02.03.2011
Researchers at the Georgia Tech Research Institute (GTRI) are developing a solid composite material to help cool small, powerful microelectronics used in defense systems. The material, composed of silver and diamond, promises an exceptional degree of thermal conductivity compared to materials currently used for this application.

The research is focused on producing a silver-diamond thermal shim of unprecedented thinness – 250 microns or less. The ratio of silver to diamond in the material can be tailored to allow the shim to be bonded with low thermal-expansion stress to the high-power wide-bandgap semiconductors planned for next generation phased array radars.

Thermal shims are needed to pull heat from these high-power semiconductors and transfer it to heat dissipating devices such as fins, fans or heat pipes. Since the semiconductors work in very confined operating spaces, it is necessary that the shims be made from a material that packs high thermal conductivity into a tiny structure.

Diamonds provide the bulk of thermal conductivity, while silver suspends the diamond particles within the composite and contributes to high thermal conductivity that is 25 percent better than copper. To date, tests indicate that the silver-diamond composite performs extremely well in two key areas -- thermal conductivity and thermal expansion.

“We have already observed clear performance benefits – an estimated temperature decrease from 285 degrees Celsius to 181 degrees Celsius – using a material of 50 percent diamond in a 250-micron shim,” said Jason Nadler, a GTRI research engineer who is leading the project.

The researchers are approaching diamond percentages that can be as high as 85 percent, in a shim less than 250 microns in thickness. These increased percentages of diamond are yielding even better performance results in prototype testing.

Nadler added that this novel approach to silver-diamond composites holds definite technology transfer promise. No material currently available offers this combination of performance and thinness.

Diamond is the most thermally conductive natural material, with a rating of approximately 2,000 watts per meter Kelvin, which is a measure of thermal efficiency. Silver, which is among the most thermally conductive metals, has a significantly lower rating -- 400 watts per meter K.

Nadler explained that adding silver is necessary to:

* Bond the loose diamond particles into a stable matrix;
* Allow precise cutting of the material to form components of exact sizes;
* Match thermal expansion to that of the semiconductor device being cooled;
* Create a more thermally effective interface between the diamonds.
Nadler and his team use diamond particles, resembling grains of sand, that can be molded into a planar form.

The problem is, a sand-like material doesn’t hold together well. A matrix of silver -- soft, ductile and sticky -- is needed to keep the diamond particles together and achieve a robust composite material.

In addition, because the malleable silver matrix completely surrounds the diamond particles, it supports cutting the composite to the precise dimensions needed to form components like thermal shims. And silver allows those components to bond readily to other surfaces, such as semiconductors.

As any material heats up, it expands at its own individual rate, a behavior known as its coefficient of thermal expansion (CTE).

When structures made from different materials – such as a wide-bandgap semiconductor and a thermal shim – are joined, it is vital that their thermal expansion coefficients be identical. Bonded materials that expand at different rates separate readily.

Diamond has a very low coefficient of thermal expansion of about two parts per million/Kelvin (ppm/K). But the materials used to make wide-bandgap semiconductors -- such as silicon carbide or gallium nitride -- have higher CTEs, generally in the range of three to five ppm/K.

By adding in just the right percentage of silver, which has a CTE of about 20 ppm/K, the GTRI team can tailor the silver-diamond composite to expand at the same rate as the semiconductor material. By matching thermal expansion rates during heating and cooling, the researchers have enabled the two materials to maintain a strong bond.

Unlike metals, which conduct heat by moving electrons, diamond conducts heat by means of phonons, which are vibrational wave packets that travel through crystalline and other materials. Introducing silver between the diamond-particle interfaces helps phonons move from particle to particle and supports thermal efficiency.

“It's a challenge to use diamond particles to fill space in a plane with high efficiency and stability,” Nadler said. “In recent years we've built image analysis and other tools that let us perform structural morphological analyses on the material we've created. That data helps us understand what's actually happening within the composite – including how the diamond-particle sizes are distributed and how the silver actually surrounds the diamonds.”

A remaining hurdle involves the need to move beyond performance testing to an in depth analysis of the silver-diamond material’s functionality. Nadler’s aim is to explain the thermal conductivity of the composite from a fundamental materials standpoint, rather than relying solely on performance results.

The extremely small size of the thermal shims makes such in depth testing difficult, because existing testing methods require larger amounts of material. However, Nadler and his team are evaluating several testbed technologies that hold promise for detailed thermal conductivity analysis.

Research News & Publications Office
Georgia Institute of Technology
75 Fifth Street, N.W., Suite 314
Atlanta, Georgia 30308 USA
Media Relations Contacts: Kirk Englehardt (404-407-7280)(kirk.englehardt@gtri.gatech.edu) or John Toon (404-894-6986)(jtoon@gatech.edu).

Writer: Rick Robinson

John Toon | Newswise Science News
Further information:
http://www.gatech.edu

More articles from Power and Electrical Engineering:

nachricht Researchers take next step toward fusion energy
16.11.2017 | Texas A&M University

nachricht Desert solar to fuel centuries of air travel
16.11.2017 | SolarPACES

All articles from Power and Electrical Engineering >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A “cosmic snake” reveals the structure of remote galaxies

The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.

Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...

Im Focus: Visual intelligence is not the same as IQ

Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.

That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...

Im Focus: Novel Nano-CT device creates high-resolution 3D-X-rays of tiny velvet worm legs

Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.

During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....

Im Focus: Researchers Develop Data Bus for Quantum Computer

The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.

Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...

Im Focus: Wrinkles give heat a jolt in pillared graphene

Rice University researchers test 3-D carbon nanostructures' thermal transport abilities

Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Ecology Across Borders: International conference brings together 1,500 ecologists

15.11.2017 | Event News

Road into laboratory: Users discuss biaxial fatigue-testing for car and truck wheel

15.11.2017 | Event News

#Berlin5GWeek: The right network for Industry 4.0

30.10.2017 | Event News

 
Latest News

NASA detects solar flare pulses at Sun and Earth

17.11.2017 | Physics and Astronomy

NIST scientists discover how to switch liver cancer cell growth from 2-D to 3-D structures

17.11.2017 | Health and Medicine

The importance of biodiversity in forests could increase due to climate change

17.11.2017 | Studies and Analyses

VideoLinks
B2B-VideoLinks
More VideoLinks >>>