Diamond firm Element Six has joined an EU-funded research project that will combine synthetic diamond and gallium nitride to create sensors and electronics for extreme environments.
Dubbed MORGaN - materials for robust gallium nitride - it is a three-year €9.2m project and involving 23 companies and universities in 11 countries. Funding comes from the EU Seventh Framework Programme.
"In relation to diamond, it is the material's excellent thermal conductivity that makes it useful as a heat spreader in device designs," said Element Six. "So one area of study will be the use of the III-Nitride material system together with polycrystalline diamond-based substrates to act as heat spreading layers."
Thermal conductivity peaks at 2,400W/m.K for single crystal diamond - the highest of any solid. Polycrystalline CVD diamond frequently exceeds 1,000. Silicon is under 150, although single crystal SiC can reach 500.
The proposal is to grow a thick layer of diamond on a silicon wafer, then remove most of the silicon leaving only a thin layer on what is now effectively a diamond substrate.
Flipping the whole thing over, GaN is now grown over buffer layers on the thin silicon.
"This gives a wafer comprising a thick diamond layer, 100µm for example, with a thin - perhaps 2-5µm - Si layer attached, and attached onto that the GaN layer," Dr Geoffrey Scarsbrook R&D manager at Element Six told Electronics Weekly.
"The devices are then fabricated in the GaN layer. The intermediate Si layer is thin enough to minimise its impact on the thermal performance, giving in effect a GaN device layer in close proximity to a diamond heat spreading layer."
One role of the firm will be to supply the consortium with diamond-based wafers suitable for III-N epitaxy.
"Element Six will use its expertise to further develop and optimise the synthesis and primary processing of silicon/polycrystalline diamond composite wafers," said company general manager Steve Coe. "The diamond synthesis and processing technologies being used by E6 to undertake MORGaN are currently a unique capability globally."
It will also prepared polycrystalline and single crystal diamond surfaces for III-N epitaxial growth.