Stanford Breakthrough Could Make Better Chips Cheaper

angry tapir writes: Researchers at Stanford University have come up with a new way to make chips and solar panels using gallium arsenide, a semiconductor that beats silicon in several important areas but is typically too expensive for widespread use. "[I]t can cost about $5,000 to make a wafer of gallium arsenide 8 inches in diameter, versus $5 for a silicon wafer, according to Aneesh Nainani, who teaches semiconductor manufacturing at Stanford. The new Stanford process (abstract) seeks to lessen this thousand-to-one cost differential by reusing that $5,000 wafer. Today the working electronic circuits in a gallium arsenide device are grown on top of this wafer. Manufacturers make this circuitry layer by flowing gaseous gallium arsenide and other materials across the wafer surface. This material condenses into thin layer of circuitry atop the wafer. In this scenario, the wafer is only a backing. The thin layer of circuitry on top of this costly platter contains all of the electronics."

Comments

The Wankel Engine of the Semiconductor Industry

[Etherwalk]

One of the very first papers I read for a VLSI design course had one of the weirdest final sentences I have ever heard, from a geeky see-my-smarts cross between physics and car geeks. As I recall, it was something like this:

"And then, of course, there is the problem of gallium arsenide, which is the Wankel Engine of the semiconductor industry."

To which the class (a bunch of undergrads wading into the delightful bliss and head-scratching geekery of academic journals for the first time) collectively and perplexedly said "WTF?"

Re:The Wankel Engine of the Semiconductor Industry

[ShanghaiBill]

I guess that would be because like Wankel engines, gallium arsenide is a better solution to the problem at hand, but won't ever get a break because the existing design is entrenched...

No, entrenched designs are not what is holding back either GaAs or Wankel engines. Although both are, in theory, elegant solutions, in practice, both have major flaws, and just don't work very well. Both have been subjected to decades of research that have not found solutions to the problems. I don't expect this research to change things much. GaAs will just go from ridiculously impractical, to very impractical. I expect to have a graphene CPU before I have a GaAs CPU.

Re:The Wankel Engine of the Semiconductor Industry

[Moof123]

Correct. As a compound GaAs is not toxic to deal with. Sodium is nasty, as is Chlorine, but combined together you can eat the stuff.

Re:No cheaper, just recyclable.

[itzly]

No, they are making a wafer, building chips on top, remove thin top layer to sell the chips, and reuse the bottom part.

Re:What makes it so expensive?

[PhunkySchtuff]

From what I understand of it (which is very little) it's relatively easy to coax a crucible of pure, molten Si to grow into a single crystal - those long grey sausage-like boules are a single crystal of silicon, so are incredibly pure with a consistent crystalline structure. It's a lot harder to get gallium arsenide to do the same thing.

Re:Why does the wafer need to be GaAs?

[DrTJ]

You need a wafer with the same crystal structure and lattice constant. If there is a mismatch
between the inter-atomic distance (aka lattice parameter or lattice constant), the atoms
deposited on this wafer will try to adjust to this lattice.

If the layer is thin, the deposited crystal will in effect be compressed or expanded. While this is OK from a mechanical and
crystal point of view, the electronic properties of the grown semiconductor will change. E.g. the bandgap (energy distance
between filled and empty energy levels) will shift, which will change the electronic properties of the material.

If/when the layer becomes thick (~5 atomic layers), the grown crystal will (try to) revert to its native lattice constant. However, there's
no ordered way to do this, so the grown crystal will contain lots of defects, or on the worst case, become amorphous
(loose its crystal structure alltogether). Defects destroy the material from an electronic point; it provides ample opportunities
for electrones and holes to recombine. It increases the leakage current and power dissipation and alse change the electronic band structure.

I haven't read the article, but what I don't understand how they intend to separate the circuitry from the wafer... it's not exactly
a tape that you can peel off, or a thick slab which you can hammer away.

the presentation is BS

[serbanp]

The article follows the youtube presentation and the summary is, for once, accurate (i.e. does not introduce new errors).

The trouble is that the presentation is utter BS. The GaAs devices are NEVER made out of a solid GaAs wafer; the process starts with a plain silicon wafer, on which GaAs is grown epitaxially. The secret sauce is, and always has been, how to minimize the defect density at the Si/GaAs interface.

Such a wafer is more expensive than the plain Si one, but not 1000x more! Oh, and every purchaser would kill to get $5 8" wafers...

Since the Stanford guys are no dummies, I guess that the announcement was deliberately made to sound ridiculous. For what purpose? Time will tell.

Re: Watched the YouTube video but left wondering..

[Anonymous Coward]

To get the single-crystal purity of the surface layers, they need to perfectly match the crystal dimensions of the substrate. Making it out of the same thing is aa easy way to achieve that.

Re:What makes it so expensive?

[K. S. Kyosuke]

There may be the issue of demand. PV cells apparently require a lot of material compared to a lot of other potential applications of GaAs (RF? Optoelectronics?). If you really started mass-producing them from GaAs, you'd start straining the global supply (200 tonnes per year or so?) long before you'd reach anything close to current global production of silicon-based PV cells.