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.
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鈥淒iamond-based control modules in electric cars and industrial machinery could lead to considerable energy savings,鈥� says Hideaki Yamada of (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 (CVD), in which a plasma of methane or other hydrocarbon gas deposits carbon onto a surface 鈥渟eeded鈥� 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 鈥� 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 鈥渃lones鈥�, all with the same crystal lattice. 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 鈥渃loned鈥� wafers (see picture).
Good enough
鈥淚t certainly has sufficient potential for fabricating electronic devices,鈥� says Yamada. Better still, 鈥渙ur method does not limit the area of the wafer鈥�, he adds. In the next 12 months his group is aiming to produce 50-by-50聽millimetre and 75-by-75聽millimetre wafers.
鈥淭heir bonding of cloned wafers into big monocrystalline mosaics is novel, interesting stuff,鈥� comments , 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 at Tokai University on 20 March.
