MIT Reports 400 GHz Graphene Transistor Possible With 'Negative Resistance' 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."
Re:And again.. (Score:5, Interesting)
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:Not negative resistance (Score:5, Interesting)
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:2000's called... (Score:2, Interesting)
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. ... 2 cores, 4 cores, 8 cores.... I can't barely figure out which chips from the same product line are better then the others.
Vs.
Intel Core i4, i5, i7 Sandy Bridge, Ivory Bridge
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.
The arc (Score:5, Interesting)
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:Not negative resistance (Score:4, Interesting)
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.