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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."
...if they can deposit a layer of GaAs on top of the sacrificial layer and make circuits out of that, then why do they need the bottom wafer at all? Why not add the sacrificial layers on something less expensive and then deposit the GaAs circuit layer on top of that?
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?"
I apologize if this was explained in TFA and I missed it; but I was left wondering why gallium arsenide would be so dramatically expensive. A quick look shows that even the scammers selling 'gallium bullion' in small quantities are charging under a dollar a gram for the stuff(at allegedly very high purity); and arsenic certainly isn't terribly pricey. Silicon, of course, is really abundant, and still fairly cheap once you've coaxed the oxygen out of the quartz-form you typically find it in; but not lower cost enough to explain a wafer-level difference as large as the one that exists.
Are gallium, arsenic, or both markedly more difficult to purify enough to serve as reliable semiconductors? Is growing sufficiently flawless crystals large enough to be cut into wafers too error prone to get good yields? Some other unpleasant aspect of processing or handling the material?
Hate filled little twit, aren't you?
Wasn't Intel announcing ga.as. as their new technology some weeks ago, for their sub-10 nano chips? I guess they must have solved the cost problem, too.
The new manufacturing method won't make the wafer any cheaper, but it does allow it to be reused roughly 50 to 100 times, dramatically reducing the per-chip cost and opening up gallium arsenide for wider use.
unless they are going to start buying back CPUs, this development means very little.
Anons need not reply. Questions end with a question mark.
Make the summary so confusing that we have to read the article? Well, I ain't falling for it! No no, not me. I know all your tricks
...when it isn't part of the finished product?
Dag B
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.
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.
Don't feed the trolls, twit.
That makes sense if you're building devices directly on the wafer, but wouldn't the three sacrificial layers interrupt that?
=Smidge=
Not even chips?
Pi * r^2 gives us 3.14 * (8in/2)^2 yields 50 square inches. Assuming each chip is 1 square inch that gives us $5000/50 or $100 of savings per chip, since the wafer can be reused.
Now we need to make a few more assumptions for the rest. Assuming ~50% circuit density and similar cost, the remaining substrate would cost around $50. That's pretty significant, especially considering that many chips will be significantly smaller than a square inch.
What is also significant is the additional weight savings.
only used ones.
News at 11.
Nope.
I believe the two materials have different thermal expansion - and that causes cracks in the top layers.
I remember a joke from about 20 years ago.
Gallium arsenide, the semiconductor of the future, and always will be.
Turns out to be true afterall.
I recall an AMD engineer presenting at MICRO in 2012 telling us that one of the problems with making wafers too thin is that they tend to curl up. I'm not sure whether the warping is inherent in the silicon or doesn't occur until after all the circuit layers are put on top. Regarding the article, the wafer doesn't start out thin. The circuits are formed, and then chips are (in a manner of speaking) shaved off the surface, exposing fresh GaAs to make another set of chips.
How exactly is this a new technique - it sounds just like vapour deposition - which has been around for several decades?
Current wanker...
Wait, what are we taking about again?
...if they can deposit a layer of GaAs on top of the sacrificial layer and make circuits out of that, then why do they need the bottom wafer at all? Why not add the sacrificial layers on something less expensive and then deposit the GaAs circuit layer on top of that?
Because the chips need to be made on single-crystal material, which needs to be grown on a single crystal substrate.
This is, by the way, not particularly new in the solar cell research community. Photovoltaics researchers have been developing technologies like this for a long time-- it's called "epitaxial lift-off" or "monolithic metamorphic" in the most recent versions (with "metamorphic" indicating a change in lattice constant), but older variants were called "cleft" and "peeled film technology".
http://www.geoffreylandis.com
Could be good stuff for GaAs circuits, but not for GaAs photovoltaics. If you're bothering to make solar cells with these materials then you're making triple-junction cells, and in that case they use a germanium wafer as the substrate, which also forms the first junction so you can't remove it from the finished device.
Not to mention pretty much everyone has a GaAs amplifier chip in their cell phone. Also CD and DVD drives use GaAs-based lasers.
Silicon has many distinct advantages over GaAs for logic. To many to go in to here.