Diamond chips to make meaner, greener electronics

The economics of the electronics industry depends on its ability to carve thousands of microchips simultaneously from silicon wafers the size of dinner plates.

A new generation of greener, more powerful electronics could be born if we could make those wafers from a material that is far superior, and incomparably more glamorous: diamond. Now it looks like we might be able to.

Pure diamond is a super-tough electrical insulator, but given the right impurities it becomes a semiconductor. Crucially, it is also the best thermal conductor on Earth. Those properties means synthetic diamond could be used to make microchips that handle high-power signals but do not require power-hungry cooling systems.

"Diamond-based control modules in electric cars and industrial machinery could lead to considerable energy savings," says Hideaki Yamada of National Institute of Advanced Industrial Science and Technology (AIST) in Tsukuba, Japan.

Sowing sparklers

Unsurprisingly, making diamond wafers big enough for economic mass production has been a stumbling block. Synthetic diamond is made using a process called chemical vapour deposition (CVD), in which a plasma of methane or other hydrocarbon gas deposits carbon onto a surface "seeded" with diamond particles. When the wafer has been grown, it is etched off the seed layer. But until now, the largest diamond wafers made like this have been around a centimetre square and a couple of millimetres thick.

To grow them further, the AIST team first tried using CVD to bond several smaller wafers together. The technique worked – but it created a patchwork of misaligned crystal lattices unsuited to making transistors.

To solve the problem, Yamada and his colleague Akiyoshi Chayahara used the same seed diamonds to make a series of small wafers, with the result that the wafers were "clones", all with the same crystal lattice/structure. Yamada and Chayahara could then use CVD to join them up seamlessly.

Using that method the team made 25-millimetre-square wafers from six smaller "cloned" wafers (see picture).

Good enough

"It certainly has sufficient potential for fabricating electronic devices," says Yamada. Better still, "our method does not limit the area of the wafer", he adds. In the next 12 months his group is aiming to produce 50-by-50 millimetre and 75-by-75 millimetre wafers.

"Their bonding of cloned wafers into big monocrystalline mosaics is novel, interesting stuff," comments Keith Rosser, a diamond CVD researcher at the University of Bristol in the UK.

A paper on the new diamond wafers was presented at a meeting of the Japan Society of Applied Physics at Tokai University on 20 March