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Gallium Arsenide Semiconductors on the Horizon
Masem writes: "According to this Chicago Tribune article, Motorola has developed a cheaper solution for putting gallium arsenide on top of silicon in order to allow for better chip designs with speeds nearly 40 times what silicon only chips would allow. While it was well known that gallium arsenide addition was favorable, it was also very expensive; Motorola's new process (covered by 200+ patents) should keep the chip prices low when these new designs are released in 2 years." The AP says they've applied for 270 patents.
There are two schools of thought when it comes to computers and the world around us.
One might say that computers and ourselves are becoming too involved with each other, us being dependant on the computers.
The other says that each technological breakthrough is a good thing, advancing us to a greater extent each time.
I subscribe to the latter view.
Taking in this point, cheaper chips are something that we should really be striving to produce. If we could come up with microchips so cheap that they cost fractions of pennies yet had the processing power of, I don't know, an Atari ST (8Mhz IIRC) then think of the places we could put them - and cheaply !
For example, The London Underground 'tube' network in England is currently trialing a new ticketing system whereby rather than having a cardboard ticket with a magnetic stripe down one side, they issue tickets which have so-called 'smart chips' inside them.
The flipside is good for LU - think how much extra effort it would be to forge a ticket.
For the everyday train user it makes life just that bit easier. No more scrabbling around for your ticket, as long as it's somewhere on your person you'll able to walk straight through the ticket barrier without having to even think about it.
Great, now maybe the G4 really will be as fast as the P4, or even faster!
Even Slashdot wants to hide some things
Am I the only one that finds it just a little bit of stretch to talk about about fantastic technology that helps to make GaAs cheaper for real life applications on the one hand -- and then mention 200+ patents on the other hand?
I know, I know, that the hope of financial gain provides the dollars for this kind of research, but let's be real: it won't be that cheap.
"Provided by the management for your protection."
Gallium arsenide chips have been around for a long time, but as the article says, they are limited to niche applications due to cost. Still, there was one company which actually shipped a mainframe built on GaAs chips -- Convex. It's actually kind of hard to find info on them these days (they were swallowed up by HP in the mid 90s), but this EE Times article has a bit of info.
Free Hans!
Back when I was a hardware guy, GaAs was a last
resort. A GaAs PAL device was 30% faster than
anything else, but it was also expensive, flakey,
hot, only available from one manufacturer, and
suffered chronic yield problems. I saw more than one product suffer in the market because of problems acquiring the single GaAs device that it used.
It looks like they're going to fix the expensive
issue; I hope that the other problems are addressed
as well.
How will this help the rest of us, the masses that don't use motorola technology? (especially when you consider the patent stuff) From what I can see, if motorola can make cheaper chips, those that don't want to use their technology will have to pay a higher premium for their chips until someone comes up with yet another (patented?) method to make things cheaper/faster.
Of course, that's probably the switching speed of GA transistors, not overall performance gains.
Does anyone know what percentage of time in the typical processor is spent waiting for transistors to switch versus simple speed-of-light propagation delays, or any other bottlenecks that this doesn't cover? In other words, how much bottom-line clock speed increase would this be likely to give?
Sometimes it's best to just let stupid people be stupid.
Nothing to see here. Move along, please.
Okay, this just happens to be the research area I work in--and I know full well the problems associated with getting high quality GaAs on Si. It's not nearly as simple as it sounds. So, it appears that Motorola found a "magical" insulating layer to put between the Si substrate and the GaAs layer. Wonderful. But it won't ever be anything but a novelty.
Here's why: In industry, everything is driven by economic margins. Plus, the pure Si industry is now very mature and they will not simply add new machinery to their processes that screw up their entire production line. That makes sense, really. Why on earth ruin a perfectly great production line just to toy around?
The other great point is final production cost. There is no way the pure Si industry will adopt a single step that is far costlier than the rest of their production line combined. Then add to the fact that those industries are adverse to any step that may slow down their production runs or cause unnecessary problems.
Sorry, people. If you want GaAs on Si, there is only one way that it can be made which will result in something the Si industry is not too adverse to. That means epitaxial growth of any buffering layers followed by high quality GaAs growth. The biggest problem that still hasn't been worked out is how does one go about making proper interconnections? Also, the buffering layer can be very conductive--and that is sometimes very hard to control. Motorola has got their heads up where it doesn't belong if they think the world is going to go crazy over this.
Long, cute, or funny Sigs are just another form of over compensation, used by geeks, nerdz, etc.
- one of my professors, ca 1983
I remember from a materials science course that GaAs semiconductors were more resistant to electromagnetic fields' influence... What kind of applications could these chips be better for than straight silicon? The military has plenty of applications... but what industries could specifically benefit from cheap electromagnetically "rugged" chips?
Hasn't Vitesse been doing Galium Arsenide semiconductors for the past 10 years?
-Ted
There's a similar article in EE times. www.eetimes.com/story/OEG20010904S0028) Sounds like they're using something called a "compliant substrate". The idea is that if the substrate is very thick relative to the film being grown then the tendency is for the film to deform it's lattice to match the substrate. The lattice strain stores energy, and as the film increases in thickness the amount of strain energy per unit volume of film increases. If the mismatch between substrate lattice dimensions and film dimensions is large enough the strain energy per unit volume can become large enough to nucleate dislocations at the interface. These dislocations allow the film to "relax" back to something near it's equilibrium lattice dimensions by periodically deleting or adding atomic planes near the interface. The problem is that these dislocations can thread up into the top of the film (i.e. where the device layers are) and act as non-radiative recombination centers and carrier traps. The dislocations can also jump from one layer to subsequently grown layers. A compliant substrate tries to force the substrate to deform, and thus the strain E in the film never gets high enough to nucleate dislocations. For example, if you make the substrate very thin then as the film grows the substrate will deform to match the equilibrium lattice dimensions of the film rahter than the other way round. Traditionally in Si technology this has been done by ion implanting O2 in a thin layer some small distance below the surface fo the wafer. The wafer is then annealed to let the crystal structure recover from all the damage the ions did to the surface. This leaves a thin layer of "single crystal" silicon floating on a thin layer of glass. At growth temperatures of >1000 C in MOCVD the glass layer is fairly gooey, and the thin silicon layer practically floats on it. So as long as the epi film is thicker than the Si compliant substrate you're golden. But this adds 2 steps to the production run, and ion implanting isn't generally a high throughput process. (i.e. $$$$$$$$$$$$$) Seems like Motorola's trick is to deposite a layer of some oxide with a crystal structure similar to GaAs. They then let oxygen diffuse down into the Si to form glass. So they bipass the implantation step. The intermediate layer probably doesn't match the GaAs exactly anyway, which means you still get dislocations. Alot fo Motorola's research time and patents were probably devoted to converting existing techniques for reducing dislocation density to work with the intermediate layer material. Anyway, I hope this gives you some idea of why I'm kinda skeptical. Old dog, maybe not-so-new tricks. But if Motorola has pulled it off it would be pretty sweet.
Butthead: I'm angry at numbers. Beavis: Yeah, there're like too many of 'em.
How come they have so many new inventions for this new chip? What - none of them could have fit on any of their older technology? Yes, I'm sure a lot of effort went into that thing, but to get over 200 new ideas on one product (especially one that is mostly an old idea that's just been too expensive before) seems amazing.
Why doesn't the gene pool have a life guard?
The second problem is the lack of a good thermal oxide in the GaAs material system. Silicon uses SiO2 which is an excellent insulator and more importantly has an extremely clean interface with silicon, so there are very few traps at the oxide-si interface. Because GaAs doesn't have a good oxide, MOS field-effect transistors (MOSFETS) are impossible and so digital GaAs chips use MESFETS, which are FETs without the oxide. It turns out the good oxide in silicon makes a lot of things possible that are impossible in GaAs. For example, the si oxide makes for a very high input impedance for Si transistors so they can be used to make dense RAM and very simple registers that rely on a high impedenence node. This structures are not possible in GaAs so more complicated, higher power circuits are required in GaAs to achieve the same functionality.
I would actually also be quite interested in the heat produced. I assume it would be higher - thus, you're not going to see them making any PPC chips out of these. However, the communication industry could benefit greatly from such devices (ie, small, simple, but very very fast.)
This all looks great but shouldn't effect the computer industry much. However, I'd still like to see Motorola's product catalog in a few years.
Willy