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MIT Reports 400 GHz Graphene Transistor Possible With 'Negative Resistance'

Unknown Lamer posted about a year ago | from the switch-faster dept.

Hardware 123

An anonymous reader writes "The idea is to take a standard graphene field-effect transistor and find the circumstances in which it demonstrates negative resistance (or negative differential resistance, as they call it). They then use the dip in voltage, like a kind of switch, to perform logic. They show how several graphene field-effect transistors can be combined and manipulated in a way that produces conventional logic gates. Graphene-based circuit can match patterns and it has several important advantages over silicon-based versions. Liu and co can build elementary XOR gates out of only three graphene field-effect transistors compared to the eight or more required using silicon. That translates into a significantly smaller area on a chip. What's more, graphene transistors can operate at speeds of over 400 GHz."

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123 comments

2000's called... (1)

Arkh89 (2870391) | about a year ago | (#44632763)

... they want their GHz war back...

Re: 2000's called... (4, Insightful)

rolfwind (528248) | about a year ago | (#44632925)

And? We're at similiar Ghz to back then but not because we want to be.

Re: 2000's called... (2)

phantomfive (622387) | about a year ago | (#44633033)

Yeah, at this point, I had basically given up hope that we would ever get above 20 Ghz. But not because I want to stay so slow.

Re: 2000's called... (1)

Anonymous Coward | about a year ago | (#44633807)

There's more to performance than just clock speed. 2 Ghz on two processors is faster than 2 Ghz on one, provided your software uses two processors. In fact, I'd say that a 2 Ghz quad core would be better than a 3Ghz single core (again assuming your software is actually using four cores....).

Re: 2000's called... (1)

Arkh89 (2870391) | about a year ago | (#44634351)

Go a little bit further, I prefer a GPU with 1K~2K+ cores running at 800MHz than a single Core at 400GHz for some purpose (simulations, image processing,...). It's not a game on who has the highest clock rate anymore but rather on who is able to fetch data at the fastest speed, who is able prevent algorithm from doing too much branching, instructions replays etc. and generally who is able to maximize throughput...

Re: 2000's called... (1)

jones_supa (887896) | about a year ago | (#44635953)

It's not a game on who has the highest clock rate anymore

Indeed. Also, when we look at normal CPUs, it's amazing how much more processing power we can get today from a 2GHz chip (e.g. an Intel Core) compared to a 2GHz chip a decade ago (e.g. a Pentium 4 chip). Same clock frequency.

Re: 2000's called... (1)

Antonovich (1354565) | about a year ago | (#44634621)

They're supposed to be smaller, so presumably you can put lots more cores on a chip than you can now. So 400GHz AND lots of cores. Bring on the singularity!

Re:2000's called... (0)

Full of shit (2908417) | about a year ago | (#44633165)

Que? 400Ghz is slower than what we had a decade ago

Re:2000's called... (5, Funny)

gagol (583737) | about a year ago | (#44633369)

Dont change your name, it serves you well.

Re:2000's called... (0)

Anonymous Coward | about a year ago | (#44633527)

Are you sure you don't mean MHz? The M and the G stand for different things, you know.

Re:2000's called... (1)

jones_supa (887896) | about a year ago | (#44636193)

Homer Simpson's head has them both [cantbeunseen.com] .

Re:2000's called... (1, Interesting)

jellomizer (103300) | about a year ago | (#44633875)

Good, less stupid marketing trying to convince us that their product is faster then the other by using some set of obscure benchmarks to compare each other.

Intel Carbon 50Ghz vs Intel Carbon 100Ghz I now what is faster.
Vs.
Intel Core i4, i5, i7 Sandy Bridge, Ivory Bridge ... 2 cores, 4 cores, 8 cores.... I can't barely figure out which chips from the same product line are better then the others.

Back in the good old days

286, 386, 486 and the number of Megahertz If your 386 had a faster megahertz then your 486 chances are for normal use it would be faster unless you use the new chip features.

Re:2000's called... (0)

Anonymous Coward | about a year ago | (#44634225)

easy, just check GFLOPS for each CPU its not 100% correct since it shows performance when program is using CPU optimally but atleast you know if its 10% better, 10% worse or 100% better than another one

Re:2000's called... (0)

Anonymous Coward | about a year ago | (#44636161)

Bogomips FTW!

Re:2000's called... (2)

localman (111171) | about a year ago | (#44635631)

I'm all for a nice and straightforward means to compare chips, but you're wrong that clock speed was a good way to do that - at least after about 1998 or so. There's just way too many other ways in which a chip can be faster or slower. Cache size, cache speed, cache prediction, instruction size, data path latency, pipelining, hyperthreading, multiple cores, etc, etc, etc.

The Pentium IV really put a stick in the idea of comparing clock speed because they actually made it do less work in each cycle so they could have more cycles per second - but the same amount of work. They intentionally inflated the clock speed just so they could fool people. That's one of many reasons my Core 2.4 Ghz smokes any Pentium IV 2.4 Ghz.

To summarize: the world is complicated and clock speed is a lousy metric. It's fine for comparing chips of the same architecture, or for comparing across chips when the clock speed difference is enormous. But no, returning to clock speed as our speed metric is not the end of stupid marketing, and the fact you thought it was just means you bought into the previous stupid collection of marketing.

Re:2000's called... (0)

Anonymous Coward | about a year ago | (#44636487)

I'm all for a nice and straightforward means to compare chips, but you're wrong that clock speed was a good way to do that - at least after about 1998 or so.

I don't disagree with your main point, but holy shit this is wrong. How on earth did you get the idea that this particular switch flipped in 1998? There was steady improvement in performance per clock cycle from the very beginning of x86 (and other microprocessor architectures). The 8086 could not execute anything in less than 2 cycles, and the vast majority of instructions took a lot more than that. The 286 improved on this in dramatic ways. The 386, even more. By the 486, extensive pipelining meant that many instructions could execute at a throughput of 1 per cycle. The Pentium introduced 2-way superscalar execution, raising peak throughput to 2/cycle (requiring careful code optimization to approach peak, but even without that it was much faster than a 486 at the same clock speed). The Pentium Pro introduced a much wider and more sophisticated superscalar out-of-order engine, raising real world throughput per clock by a lot and requiring much less hand optimization than Pentium. So on and so forth.

It's not a recent thing. Clock speed has never been a good way to directly compare two CPUs of substantially different design.

The Pentium IV really put a stick in the idea of comparing clock speed because they actually made it do less work in each cycle so they could have more cycles per second - but the same amount of work. They intentionally inflated the clock speed just so they could fool people. That's one of many reasons my Core 2.4 Ghz smokes any Pentium IV 2.4 Ghz.

Snarky response: That's an intentionally simple-minded view of the issues.

Was there some marketing motivation to the pursuit of high clock speeds? Perhaps. But it's not a fundamentally dishonest way of increasing performance. Pentium IV was neither the first nor the last time in history that a CPU design team has tried the so-called "speed racer" path, because in a vacuum, what do you care whether your CPU is fast because it has a high clock or because it's got a really sophisticated but slower-clocked core (aka a "braniac" in the biz)? You don't, the performance is what matters, and in that sense the Pentium IV actually delivered for several years. It eventually ran out of gas because advances in semiconductor physics didn't turn out the way they traditionally had. Instead of new process nodes making it possible to crank up clock rates while keeping power down (as they always had before), P4-like architectures were doomed to start using disproportionately more power than braniac CPU cores for the same performance. Late model Pentium 4 chips should've clocked much faster than they did (as in, Intel had planned to hit at least 5 GHz by then), but had to be held back to keep power consumption reasonable.

Also, a 2.4 GHz Core 2 has 4.5 years and two full process nodes on a 2.4 GHz Pentium IV. P-IV was able to hit speeds as high as 3.0 GHz in Intel's 130nm process. In 2002. That's impressive, no matter how much you want it not to be. There was some really interesting and novel engineering which went into Pentium IV. Ultimately a wrong turn, but that happens.

1990's called... (1)

wonkey_monkey (2592601) | about a year ago | (#44636431)

...they want their joke back.

Jokes called... (1)

fisted (2295862) | about a year ago | (#44636625)

...they want their 1990s back.

And again.. (1)

Covalent (1001277) | about a year ago | (#44632771)

...graphene saves the world, creates amazing superproducts, and almost defies the laws of physics.

Cynicism aside, the research is exciting, but it's not likely to bear fruit any time soon.

Re:And again.. (1)

i kan reed (749298) | about a year ago | (#44632955)

Well, if you want something to feed your cynicism, it's pretty reasonably supported that graphene causes cancer, if it gets in your body.

Re:And again.. (1)

Anonymous Coward | about a year ago | (#44633817)

I read a research paper that said if you took graphene in suppository form it could not only cure cancer but freshen your breath too.

Re:And again.. (0)

Anonymous Coward | about a year ago | (#44634823)

any suppository that manages to freshen your breath is almost certainly inserted too deeply....

Re:And again.. (4, Interesting)

smaddox (928261) | about a year ago | (#44632973)

You're cynicism is valid in this case. This is just rehashing research from 20 years ago on negative differential resistance (NDR) two-terminal devices. CMOS won out because it scales much better. Graphene is a horrible material for traditional logic; it has no bandgap. Graphene switches have an on-off current ratio of ~3 (tiny and useless), whereas similar sized silicon-based MOSFETs have on-off current ratios of ~1000.

There is some interesting work on making a new kind of logic with graphene-based BiSFETs, but it's still not possible to actually fabricate them. In contrast, neuristors, which are another interesting form of nanoscale logic, have been fabricated by HP labs from Mott-insulator based memristors. If I had to put my money on a replacement for CMOS, it would be these neuristors. However, there are still huge engineering challenges that lay ahead. Nonetheless, the Mott-insulator based memristors are already being commercially developed for high density, solid-state memory, with the hopes of eventually replacing flash memory.

Re:And again.. (4, Informative)

yesterdaystomorrow (1766850) | about a year ago | (#44633903)

You're cynicism is valid in this case. This is just rehashing research from 20 years ago on negative differential resistance (NDR) two-terminal devices.

Logic based on two terminal NDR devices has been around for more than 50 years (tunnel diodes, neon tubes, ...). Its big problem is input-output isolation: cascading elements is tricky. But these guys are using four terminal devices in a three terminal NDR mode, so they don't have that problem.

Graphene switches have an on-off current ratio of ~3 (tiny and useless),

Well, that depends. The ECL gates that Cray used for their early supercomputers had nearly constant current. Some specialized applications still use ECL. If you're changing state frequently, low static current may not actually save power. So, if this new technology ever becomes practical, you'll see it in fast clocking cores where essentially every gate and flip flop is busy all of the time. The surrounding support circuits will still be silicon.

Re:And again.. (1)

phantomfive (622387) | about a year ago | (#44634105)

So, if this new technology ever becomes practical, you'll see it in fast clocking cores where essentially every gate and flip flop is busy all of the time. The surrounding support circuits will still be silicon.

Heh, so the internal logic is running at 400GHZ, and the rest of the chip is running at 10GHZ? Is that even practical?

Re:And again.. (1)

Anonymous Coward | about a year ago | (#44634233)

Your CPU already operates at different speeds for different instructions, uses the cache at a slower rate, uses your RAM at an even slower rate and your disk an an even slower rate.

Re:And again.. (1)

profplump (309017) | about a year ago | (#44634285)

Heh, so the internal logic is running at 400GHZ, and the rest of the chip is running at 10GHZ? Is that even practical?

That's the way most systems have worked since the 486@66MHz days.

Re:And again.. (1)

yesterdaystomorrow (1766850) | about a year ago | (#44634301)

So, if this new technology ever becomes practical, you'll see it in fast clocking cores where essentially every gate and flip flop is busy all of the time. The surrounding support circuits will still be silicon.

Heh, so the internal logic is running at 400GHZ, and the rest of the chip is running at 10GHZ? Is that even practical?

Yes. Clock speed mismatch in different parts of a system is common with current technology. Cores commonly clock faster than memories, and much faster than many peripherals.

Re:And again.. (1)

K. S. Kyosuke (729550) | about a year ago | (#44635093)

I'd say it's not only practical but semi-asynchronous circuitry/multiple clock domains are already being used in CPUs. Your cores are already independent in their clock frequency, and I'd assume that shared caches are independent, too, since they can't actually be clocked against any single core.

Re:And again.. (1)

Anonymous Coward | about a year ago | (#44636849)

Heh, so the internal logic is running at 400GHZ, and the rest of the chip is running at 10GHZ? Is that even practical?

Some other folks have covered the fact that it's not unusual to interface wildly differing clock rates. The other thing to keep in mind is that whenever device researchers quote ludicrously high speeds, they're talking about the speed at which an individual transistor can switch states (because that's what their research is focused on). Real logic circuits are always at least an order of magnitude slower. They're built up from many transistors, many of which are organized serially, so the switching delays add up. Furthermore, the wiring used to connect these chains together also has significant delay.

I don't have a great feel for the numbers on the ASIC side since I usually work with FPGAs, so I'll give you an FPGA example which illustrates the principle. SRAM FPGAs use SRAM "lookup tables" (LUTs) to implement arbitrary logic: if you have N bits of inputs, you can represent any function of those N bits with a 2^N bit deep 1-bit wide lookup table, using the N input bits as an index into the table.

Smoothing over some irrelevant details, modern Xilinx FPGAs are arrays of 6-input LUTs (64x1 SRAMs) paired with flip-flops (clocked storage elements), all interspersed with a programmable routing fabric which can connect the dots in arbitrary ways. If you look up the datasheet value for combinatorial logic delay (i.e. the time it takes from changing any of the inputs to a LUT to when the output reflects the correct value), it's really fast -- as fast as 50 picoseconds. Does that mean you can run real circuits implemented in such a FPGA at 1/50ps = 20 GHz? Oh hell no. With lots of tender love and care you can maybe hit 500 MHz. Maybe. But it's very, very difficult. Most routing delays are at least a couple hundred picoseconds, more if the signal has to travel further than neighbor distance in the routing matrix, so to even do as good as 500 MHz you have to take a lot of care to ensure that no logic function is so complex that it has to be implemented with multiple LUTs chained together, and that everything can be packed close together. 1 GHz is forget-about-it territory.

Re:And again.. (1)

Agripa (139780) | about a year ago | (#44634797)

If you exclude the integration issues, then you can go further back to 1959 with the GE Tunnel Diode Manual which discusses two-terminal negative differential resistance logic.

Since the speed was limited by the lead inductance of the discrete parts, I wonder how well an integrated version would perform. I suspect integration density would be limited by power dissipation as usual but integrated tunnel diode logic would sure be fast.

Re:And again.. (1)

smash (1351) | about a year ago | (#44633063)

Maybe, maybe not. Intel have been hinting that they won't be using silicon for much longer, a couple of years back they said there was maybe 3-4 generations of CPU left that they were going to do in silicon and that they had something "Really cool" in the lab to replace it with.

Re:And again.. (2)

meta-monkey (321000) | about a year ago | (#44633123)

I'm really hoping it's isolinear chips.

Re:And again.. (0)

Anonymous Coward | about a year ago | (#44633759)

I'm really hoping it's isolinear chips.

Don't be absurd, they need to invent duotronic relays first.

Re:And again.. (-1)

Anonymous Coward | about a year ago | (#44633419)

Gratz, your sig is the most arrogant and just plain stupid one I've seen in a year. You're likely more myopic than someone with a quarter of your experience.

Re:And again.. (2)

aaronb1138 (2035478) | about a year ago | (#44635263)

Intel dropping hints like that is just as likely to be sending their competition down fiscal rabbit holes searching for the "really cool" stuff.

Whatever (0)

Anonymous Coward | about a year ago | (#44632779)

Call me when it will interface with my existing duotronic relays

400GHz? (0)

Anonymous Coward | about a year ago | (#44632787)

Eat that, Moore!

Re:400GHz? (1)

phantomfive (622387) | about a year ago | (#44633025)

Given the early state of this technology, it could well be that this technology doesn't get into your computer until the time it would match Moore's law (ignoring of course, that Moore's law deals with transistor size, not clock speed).

Re:400GHz? (0)

Anonymous Coward | about a year ago | (#44633159)

Given the early state of this technology, it could well be that this technology doesn't get into your computer until the time it would match Moore's law (ignoring of course, that Moore's law deals with transistor size, not clock speed).

Actually, if Moore's law would deal with clock speed, this would me more like reality catching up [wordpress.com] to it, after the current clock speed stagnation.

Re:400GHz? (2)

phantomfive (622387) | about a year ago | (#44633229)

That graph makes me sad

Re:400GHz? (2)

amRadioHed (463061) | about a year ago | (#44633907)

FYI, here's [wordpress.com] the full post where the graph came from.

Re:400GHz? (1)

jellomizer (103300) | about a year ago | (#44633933)

However we got more Cores. So there is more parallel processing going on.

Bad if you are still using DOS, but we learned to open up a bunch of apps without worrying anymore.

Re:400GHz? (1)

jones_supa (887896) | about a year ago | (#44636297)

Hey, DOS was awesome. You could concentrate well on one thing at a time and get stuff done. Hardware-accelerated text console at your fingertips. Direct fast hardware access. Very fast startup.

Re:400GHz? (1)

SuricouRaven (1897204) | about a year ago | (#44636023)

The focus shifted from more MHZ to doing more with them. Mostly parallelisation, more specialised hardware abilities and more efficient pipelining.

Still sucks for those algorithms that can't be made parallel, though.

I`ll take 2 (0)

Anonymous Coward | about a year ago | (#44632799)

How long before I can build a PC out of it?

I've been waiting so long to play Crysis 1 at 60+ FPS full quality... in fact, Crysis 1, is the reason, I stopped updating my PC... this is my benchmark game.

Re:I`ll take 2 (2)

bobbied (2522392) | about a year ago | (#44633357)

A LONG time. Graphene is not even close to prime time yet. It leaks current like a colander leaks water and has such low gain (current or voltage take your pick) to make it nearly useless as a switch. Graphene *might* find use in broadband RF amps at lower power, but it's going to waste huge amounts of energy and you won't get much gain in the process. I'm not sure what value it will be, even in that application.

They are going to have to come up with some modifications to the graphene crystal structure to make it not leak current and leave the desirable characteristics in place before this is going to be viable in digital devices. Given the materials engineers have been going after this for decades and have not yet come up with a solutions, I'm not holding out much hope for an easy solution.

Silicon is indeed unique, in it's character and location on the Periodic Table. We will be hard pressed to come up with something that is as usable in digital electronics to replace silicon. We might be able to engineer a material that is useful and graphene does have promising aspects. but it's a long way from "shows promise" to "you can buy it".

Re:I`ll take 2 (1)

geekoid (135745) | about a year ago | (#44635699)

they solved that in 2012. Do try to keep up.

Re:I`ll take 2 (1)

Luckyo (1726890) | about a year ago | (#44634147)

Your graphene question has been addressed by bobbied, and the answer to your other question is: right now. Modern GPUs can produce constant 60+FPS on crysis 1 at full details quite easily. In fact, they can do that for crysis 3 (think nvidia titans in sli). It'll just cost you quite a lot. But it's already doable.

The next stage is going to be 4k rendering, and for that, we're not quite at 60FPS+ yet. Though there we are not only hitting the output of modern GPUs, but even the GPUmonitor interface starts to be pushed to the limits.

Re:I`ll take 2 (0)

Anonymous Coward | about a year ago | (#44634521)

even the GPUmonitor interface starts to be pushed to the limits.

solved problem, multiple links for each monitor (think 2 or 4 dulaDVI or displayport links for each monitor from PC) each link controls 1/2 or 1/4 of display and OS "merges" them for applications into 1 display

how much watt do you need for 400Ghz? (1)

Anonymous Coward | about a year ago | (#44632807)

k.T.

Re:how much watt do you need for 400Ghz? (0)

Anonymous Coward | about a year ago | (#44636099)

slashdotters are too stupid to answer such a question....

even better: (0, Funny)

Anonymous Coward | about a year ago | (#44632821)

I don't know about this computer stuff, but graphene lube is much better than silicone lube. I say, bring on the graphene trannies!

Insecure Passwords will Be Toast ... (0)

BoRegardless (721219) | about a year ago | (#44632827)

Once these transistors make up a functional computer &/or computer network.

Plenty of jobs for security specialists are ensured.

Re:Insecure Passwords will Be Toast ... (0)

deaf.seven (2669973) | about a year ago | (#44632885)

Sometimes I wonder how relevant parallel programming would be with 100GHz - 1000Ghz or more CPUs available.

Re:Insecure Passwords will Be Toast ... (1)

camperdave (969942) | about a year ago | (#44632937)

Don't worry. They'll build Graphene GPUs at the same time as they build CPUs out of them. I'm still waiting for the low power, sunlight readable, full color displays to come out.

Re:Insecure Passwords will Be Toast ... (1)

smash (1351) | about a year ago | (#44633103)

I suspect they wont immediately. More likely they will cut costs and instead of having 4 or 8 cores on your CPU, you'll have ONE, just clocked higher. a single core is a LOT less complex to program for, and it will run fast enough that it doesn't matter for some time. ditto for GPUs. I suspect you'll see the designs simplified, consuming less power, etc long before we see similar complexity designs to today on graphene.

A major reason is that the software just isn't there yet.

Re:Insecure Passwords will Be Toast ... (1)

mwvdlee (775178) | about a year ago | (#44633755)

Why couldn't they make an x86-64 compatible CPU using this (or in fact, any other) CPU technology?

Perhaps the first few CPU's will be custom a ISA, but after they learn how to build full CPU's with this technology, there is nothing stopping them from making ARM or x86-64 compatible CPU's.

Re:Insecure Passwords will Be Toast ... (1)

Stormy Dragon (800799) | about a year ago | (#44633937)

Even if it is a custom ISA, at 400GHz I'm pretty sure it can just emulate any existing CPU without even breaking a sweat.

Re:Insecure Passwords will Be Toast ... (1)

geekoid (135745) | about a year ago | (#44635721)

And they'll a a linux distro in a week.
And Apple will change their architecture 2 years later.

Re:Insecure Passwords will Be Toast ... (0)

Anonymous Coward | about a year ago | (#44635427)

Why bother with compatibility to x86-64 or ARM? We can recompile our os & apps for any cpu already. Linux runs on 15 architectures already, one more is not a problem. Oh, and commercial vendors can recompile for new platforms too.

Re:Insecure Passwords will Be Toast ... (1)

Anonymous Coward | about a year ago | (#44632985)

When your DRAM still has nanosecond-level access times, it's still pretty relevant.

Re:Insecure Passwords will Be Toast ... (0)

Anonymous Coward | about a year ago | (#44633071)

When your DRAM still has nanosecond-level access times, it's still pretty relevant.

What about on die cache?
Most cracking processes try to leverage that as much as possible and (i think) can do whole sha512 hashes without needing much from ram.

Re:Insecure Passwords will Be Toast ... (1)

Zero__Kelvin (151819) | about a year ago | (#44633285)

It would still be extremely relevant, since not all compute problems are sequential in nature. For example, I may want to repaint my screen at the same time as I calculate the values required rather than calculating all the values first and then finally starting the repaint. 5 truly parallel processes at 1hz is five times as efficient, just as 5 truly parallel processes at 500 Ghz is 5 times more efficient. If history has taught anything with computers it is that we are far from having more computing power than we can find a use for.

Re:Insecure Passwords will Be Toast ... (1)

DexterIsADog (2954149) | about a year ago | (#44633443)

Of course, 1,000 GHz should be fast enough for anyone...

Holy shazbot 400ghz (0)

Anonymous Coward | about a year ago | (#44632917)

The engineering required for communications in the low 10s of gigahertz is already mind boggling, but 400? There's a reason EE's call the high freqency RF engineers voodoo shamen. I've seen teartowns of high freqency RF equipment on youtube and the stuff looks like alien technology or props out of a sci-fi movie. Half the time it's just creatively drawn traces on a PCB covered by a metal sheild. "That squiggle? That's an inductor. That one? A capaitor? That jagged line is a carefully tuned multiplexer" And then there are waveguides.. Things that look like chunks of (and really are) oddly square metal tubing that cost 1500 hundred bucks a pop.

Strange stuff.

Not negative resistance (5, Informative)

Anonymous Coward | about a year ago | (#44632935)

"in which it demonstrates negative resistance (or negative differential resistance, as they call it)"

Negative resistance and negative differential resistance are not the same thing. Negative resistance would mean the current flows against the voltage. Negative differential resistance just means that the current goes down when you increase voltage.

The first one is not possible (unless you've got an external energy source driving the current) because it would imply a perpetuum mobile. The second is unusual, but doesn't violate any fundamental laws of the universe.

Re:Not negative resistance (4, Funny)

Anonymous Coward | about a year ago | (#44633099)

How can you get anyone to read an article on science if you don't convince them you are violating the fundamental laws of the universe?

Re:Not negative resistance (1)

Nemesisghost (1720424) | about a year ago | (#44633243)

How can you get anyone to read an article on science if you don't convince them you are violating the fundamental laws of the universe?

Heck, that's half the reason to read Hitchhiker's Guide to the Galaxy.

Re:Not negative resistance (5, Interesting)

ShanghaiBill (739463) | about a year ago | (#44633199)

Negative differential resistance just means that the current goes down when you increase voltage.

Interestingly, the entire electric grid is developing NDR, and that is a big problem for power companies. In the old days, if there was too much demand for electricity, or if transformers were overheating, the power company could reduce the voltage (a "brown-out") and the current would fall. But with more and more switching power supplies in electronics and fluorescent lights, that doesn't work as well anymore. The switching power supply in your computer and CFLs will compensate for reduced voltage by increasing the duration of the "on" phase of the switch, thus drawing additional current, the opposite of normal resistance.

Re:Not negative resistance (3, Interesting)

SuricouRaven (1897204) | about a year ago | (#44636073)

I'm waiting to see what abuses show-off hackers can carry out with that. Not hacking the grid itsself, but the devices. Think a virus that infects the top five lines of electric car in 2030 and tells them all to flatten their batteries one night, then all simutainously kick in fast-charge mode at precisely the peak of the normal morning cuppa-tea surge. From low load to a couple hundred gigawatt above normal in five seconds. Grid wouldn't be able to react in time, substations would shut down automatically to prevent damage, could take hours to bring everything back up manually.

The arc (4, Interesting)

dtmos (447842) | about a year ago | (#44634033)

A little-known example of negative differential resistance is the common electric arc. In an arc, as the current increases the arc gets "fatter" (wider), and so the voltage across the arc decreases. Increasing current with decreasing voltage is negative differential resistance. This enables oscillations, which were first encountered as audio noise in electric arc lighting in the mid-1800s. These led to William Duddell's "Singing Arc" [wikipedia.org] , in which Duddell added a tuned circuit to the negative resistance, creating a stable audio tone. The next step was obvious; he wired a keyboard to the arc and made the first electronic music.

Danish physicist Valdemar Poulsen took Duddell's audio oscillator and, by placing the arc in a transverse magnetic field, and in a hydrogen atmosphere (and somehow not getting blown up in the process), moved the frequency of oscillation up into the low radio range, around 500 kHz or so. This was the arc radio transmitter. It differed from the more common spark transmitter in that the arc's output oscillation was continuous, while that of the spark transmitter was a damped (decaying) oscillation.

The arc transmitter caught the attention of Cyril Elwell, of Palo Alto, California, who arranged to obtain the rights to the arc from Poulsen, and started commercial production of it with his company, the Federal Telegraph Company. The arc transmitter became a big success in World War One, when transmitters as large as 1 MW (one million watts) output were installed by 1918.

Much as the Fairchild Semiconductor Company spawned several successful companies in Silicon Valley in the 1960s, Federal did so, too, 50 years earlier; refugees from Federal formed well-known companies like Magnavox and Litton Industries.

Re:The arc (1)

H0p313ss (811249) | about a year ago | (#44634193)

Danish physicist Valdemar Poulsen took Duddell's audio oscillator and, by placing the arc in a transverse magnetic field, and in a hydrogen atmosphere (and somehow not getting blown up in the process), moved the frequency of oscillation up into the low radio range, around 500 kHz or so. This was the arc radio transmitter. It differed from the more common spark transmitter in that the arc's output oscillation was continuous, while that of the spark transmitter was a damped (decaying) oscillation.

I learned something on Slashdot, my day is done.

(I'm a software geek, so my electronics only had to go as far as a wheatstone bridge [wikipedia.org] . Which is kind of embarrassing when you consider that my grandfather was an electrical engineer, I'll bet he could have whipped up an arc transmitter for fun.)

Re:Not negative resistance (0)

Anonymous Coward | about a year ago | (#44636383)

The first one works fine if you use positrons.

negative diff. resistance != negative resistance (0)

Anonymous Coward | about a year ago | (#44632957)

Crap, it looks like the editors(!) are computer scientists.

CAPTCHA: cathodes

How was the estimation of 400 GHz made? (1)

vovick (1397387) | about a year ago | (#44632987)

And what prevents silicon transistors from operating at frequencies over 400 GHz in theory? I'd much very like to know the answer before gasping in excitement. Something is telling me this estmiation has very little to do with the current technological level we have now...

Re:How was the estimation of 400 GHz made? (4, Informative)

smpoole7 (1467717) | about a year ago | (#44633151)

>And what prevents silicon transistors from operating at frequencies over 400 GHz in theory?

http://en.wikipedia.org/wiki/Electron_mobility [wikipedia.org]

Simply put, electrons (and holes, if you're looking at the other way) can only move so quickly through a given material.

Re:How was the estimation of 400 GHz made? (1)

vovick (1397387) | about a year ago | (#44634557)

The article you have linked to does not provide the definitive answer as to what the relation between the estimate in maximum frequency and electron mobility is. So it is not clear to me that silicon transistors cannot achieve 400 GHz. It is intuitive to conclude that the faster an electron can move through a material, the faster it can oscillate, and the higher you can crank up the frequency, so max estimation in frequency for Si is most likely lower than the one in graphene. But, again, I cannot find an estimation of max frequency for the silicon and, moreover, I expect it to be much higher than current processor frequencies, contrary to what the summary seems to imply.

Re:How was the estimation of 400 GHz made? (1)

geekoid (135745) | about a year ago | (#44635829)

The article has the damn formula in it.
What you mean to say is you aren't smart enough to use it.
The actual number will depend on the doping.
for example:

Doping cm-3 = 10 to the -14
Electron Mobility (cm2 V-sec) ~ 1500
Hole Mobility (cm2 V-sec) ~ 450

doping has a big impact on the numbers.

Even if you could get Silicon to 400Ghz, the amount of power and heat would be a lot hire the graphene

If you need it simpler then that, then you're too ignorant to have an opinion on this topic.
Yeah, I'm rude but I am tired of people rendering opinions about things they know nothing about.

Re:How was the estimation of 400 GHz made? (1)

vovick (1397387) | about a year ago | (#44636283)

The article has the damn formula in it.

What formula? I asked for the estimation of the maximum frequency for a silicon-based transistor. A formula, along with the way it could be derived, would do. I looked for the word "frequency" in the article, yet I did not find anything directly describing said equation.

Doping cm-3 = 10 to the -14
Electron Mobility (cm2 V-sec) ~ 1500
Hole Mobility (cm2 V-sec) ~ 450

All right, you copied some numbers from the article. How are they related to the estimated maximum frequency of a transistor?

Even if you could get Silicon to 400Ghz, the amount of power and heat would be a lot hire the graphene

I asked if it was theoretically possible. The article implied it was not, and that was the reason for my question. As other people have already said, "the amount of power and heat" for Silicon can be negligible at 400GHz as well, so this is a very weak and unrelated argument.

Yeah, I'm rude but I am tired of people rendering opinions about things they know nothing about.

And I'm tired of Internet dimwits that are unable to reason and who are ready to insult other people's brain capabilities any time they are unable to read and comprehend their posts.

teleportation (1)

electrosoccertux (874415) | about a year ago | (#44635031)

that's what's great about bandgaps in silicon. The electron doesn't travel, it teleports.

Re:How was the estimation of 400 GHz made? (1)

slew (2918) | about a year ago | (#44636715)

>And what prevents silicon transistors from operating at frequencies over 400 GHz in theory?

http://en.wikipedia.org/wiki/Electron_mobility [wikipedia.org]

Simply put, electrons (and holes, if you're looking at the other way) can only move so quickly through a given material.

It's a bit more complicated than that if you are looking for an "ultimate" limit.

Electron mobility is important when considering the charge drift-velocity limited performance of a transistor (e.g., in a typical sub-micron device of today), but for nano-scale transistors, ballistic charge transport is predicted to be an important factor in charge transfer. Basically instead of operating in an ohmic region where charge motion is modeled by a drift equations and limited by channel scattering effects, in ballistic transport, the charge (or holes) move pretty much unimpeded from source to drain (or vice versa) because of the local field configuration or local quantum potential reasons. Since the ballistic transport is more limited by geometry than the channel composition, it's not clear that the ultimate limit is much different except that you can have higher current levels in graphene for "wires" connecting these switching components (because the wires probably don't need to be connected by "ohmic" contacts to the transistors).

In any case, this paper doesn't really take this angle, but instead posits a modified type of switching element based on connecting and biasing a graphene transitor into a region where the Negative Differential Resistance effect happens (higher voltage, lower current) so that you don't have to rely on an intrinsic band-gap in the material to have a sharp on/off switching. As long as the NDR effect is high enough and you bias everything appropriatly, the on-off current ratio can be significant allowing a practical device to be manufatured The two interesting thing about the paper, are...

1. They theorize that the graphene NDR effect can be used in the nano-scale ballistic regime (even though their experimental device wasn't small enough and only operated in the drift regime) meaning it's not doomed to be out-scaled by silicon...
2. The device configuration that is required to use NDR is also suited for some non-binary computation schemes (e.g., fuzzy or multi-level primitives) mean it has some intrisnic efficiency over traditional transistors for some types of problems...

FWIW, There are other non-graphene materials that make use of NDR effects. Probably the most common example is Gunn diode which is used to make high-speed oscillators (GaN versions can oscillate in the Terahertz range) for various low-power radar transmitters. Of course oscillating isn't really switching, but the principles are very similar. For a while, there was some research on SOI (silicon on insulator) devices which used NDR-capable FETs, but I don't think these used they same type of device topology proposed here...

Re:How was the estimation of 400 GHz made? (1)

Nemesisghost (1720424) | about a year ago | (#44633271)

It is because you can't make the electrons move fast enough to switch between the different energy states without melting the entire thing.

Re:How was the estimation of 400 GHz made? (1)

SuricouRaven (1897204) | about a year ago | (#44636273)

Silicon transistors can run at 500GHz* - but that's hitting the limits of electron mobility, and it needed liquid helium cooling.

Sometimes, liquid nitrogen just doesn't cut it.

* http://gtresearchnews.gatech.edu/newsrelease/half-terahertz.htm [gatech.edu]

Re:How was the estimation of 400 GHz made? (1)

vovick (1397387) | about a year ago | (#44636567)

Thank you, I did not notice your comment before posting the same link. I wonder how much better graphene will do at such frequencies and temperatures and how much of a breakthrough there is behind this summary blurb.

Re:How was the estimation of 400 GHz made? (1)

vovick (1397387) | about a year ago | (#44636497)

Answering my own question: nothing prevents silicon transistors from working over 400 GHz. IBM & GeorgiaTech have already done that.
http://gtresearchnews.gatech.edu/newsrelease/half-terahertz.htm [gatech.edu]
http://www-03.ibm.com/press/us/en/pressrelease/19843.wss [ibm.com]
As it has been mentioned by user mc6809e in another comment, certain transistors have long since reached 1 THz, but I'm unqualified in the area and can't find the appropriate article or key words.

Keeping my excitement for some other occasion.

Summary incorrect - Don't need 8 transistors in Si (3, Informative)

craighansen (744648) | about a year ago | (#44633041)

Two NMOS transistors and a resistor can perform an XOR in Si. I remember interviewing at Intel in 1980, and every damn interview question was about XOR gates. First was an XOR gate in TTL, then an XOR gate in CMOS, and finally an XOR gate in NMOS. Apparently I passed all three questions, 'cause they offered me a job.

Re:Summary incorrect - Don't need 8 transistors in (5, Funny)

Impy the Impiuos Imp (442658) | about a year ago | (#44633471)

NAND? Don't leave us hanging.

Re:Summary incorrect - Don't need 8 transistors in (2)

Em Adespoton (792954) | about a year ago | (#44634583)

That wasn't the only part of the summary that was wrong; about the only part that was correct was the part that stated that they were able to perform an XOR in graphene with 3 FETs due to negative differential resistance.

Not MIT's work (4, Informative)

Anonymous Coward | about a year ago | (#44633115)

MIT may have reported it, but the research comes out of UC Riverside. Give credit where credit's due; interesting research isn't only done at MIT, Stanford, or Cambridge.

alisha01 (-1, Offtopic)

alisha01 (3026467) | about a year ago | (#44633657)

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Tunnel Diodes (2)

Gim Tom (716904) | about a year ago | (#44633675)

Does anyone else remember this same kind of thing being said about Tunnel Diodes several decades ago? There were very few things actually sold with Tunnel Diodes in them. The only one I have is a very old Heathkit dip meter which never did work very well. Negative Resistance devices seem to keep popping up from time to time, but they also seem to be very difficult to get to work in a real circuit.

Re:Tunnel Diodes (0)

Anonymous Coward | about a year ago | (#44633837)

Yeah, the problem with Tunnel diodes is that they're two-terminal devices, so the input is in parallel with the output. That makes it really hard to have well-defined input and output ports. You can make them oscillate and flip from one state to another, but it's really hard to make them amplify.

Also I think they had to be made by hand, from Germanium, which made them expensive and unstable.

Re:Tunnel Diodes (1)

H0p313ss (811249) | about a year ago | (#44634245)

Also I think they had to be made by hand, from Germanium, which made them expensive and unstable.

#import <std_ex_wife_joke>

Only over 400 GHz? (1)

chris200x9 (2591231) | about a year ago | (#44633709)

Call me back when it's over 9000 GHz.

Silicon is already there (4, Informative)

mc6809e (214243) | about a year ago | (#44633757)

Silicon transistors with sub picosecond switching times were fabricated in 2002. That's in the THz range.

What holds back processors today is mostly the RC delay of metal wires.

Re:Silicon is already there (2)

vovick (1397387) | about a year ago | (#44634885)

Thank you for clearing this up. I've asked above why silicon (or silicon with some additions) cannot reach the theoretical threshold of 400 GHz the summary seems to make such a big deal of and didn't get a clear answer. Turns out it can and that theoretical frequency, as somehow expected, is not the limiting factor for modern processors.

Re:Silicon is already there (1)

geekoid (135745) | about a year ago | (#44635849)

So people showing you the link with the math doesn't cut it, but some random post that agrees with you does?
I bet you believe your mother when she said you where a smart boy.

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