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MIT Reports 400 GHz Graphene Transistor Possible With 'Negative Resistance'
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."
http://xkcd.com/678/
And? We're at similiar Ghz to back then but not because we want to be.
"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.
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.
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.
"First they came for the slanderers and i said nothing."
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.
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.
I'm really hoping it's isolinear chips.
We don't have a state-run media we have a media-run state.
>And what prevents silicon transistors from operating at frequencies over 400 GHz in theory?
http://en.wikipedia.org/wiki/Electron_mobility
Simply put, electrons (and holes, if you're looking at the other way) can only move so quickly through a given material.
Cogito, igitur comedam pizza.
That graph makes me sad
"First they came for the slanderers and i said nothing."
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".
"File to fit, pound to insert, paint to match" - Aircraft Maintenance 101
Dont change your name, it serves you well.
Tomorrow is another day...
NAND? Don't leave us hanging.
(-1: Post disagrees with my already-settled worldview) is not a valid mod option.
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.
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.
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.
FYI, here's the full post where the graph came from.
We hope your rules and wisdom choke you / Now we are one in everlasting peace
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", 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.
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.
Intel dropping hints like that is just as likely to be sending their competition down fiscal rabbit holes searching for the "really cool" stuff.
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.