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IBM Creates Ring Oscillator on a Single Nanotube
deeptrace writes "IBM has combined CMOS circuitry and a single carbon nanotube to implement a 5 stage ring oscillator. Even though the oscillator runs at just 52 MHz, they expect that it could reach the GHz range with improvements. The frequency of the current oscillator was higher than previous circuits using multiple nanotubes. IBM describes the achievement in the paper "Integrated Logic Circuit Assembled on a Single Carbon Nanotube" to be published this week in the journal Science."
Religion for nerds. Stuff that really matters
Most semiconductors only turn on at a certain voltage level. For example, most silicon transistors turn on at about positive 0.7 volts. Any less than that and the trasistor won't conduct, even if you go below 0 volts to a negative voltage.
What the person was saying about nanotubes is they will "turn on" or begin to conduct again after the voltage drops below 0 to a certain negative level. Kind of like a device that takes the absolute value of the voltage, and if it's above a certain value it conducts or switches "on".
-- You are in a maze of little, twisty passages, all different... --
Ring oscillators are simple circuits with which you can easily compare different circuit technolgoies. You simply scale the circuit to whatever your new design rules are, say 90 nm -> 65 nm, soi, etc. and measure the new frequency of the oscillator. This gives you a good base point for measuring and comparing the performance of the new technology.
FYI - a ring oscillator is just a proof of concept and there is no practical application, per se. It shows that their carbon nanotube transistor technology is well understood enough so that they can make simple logic devices (an oscillator is a bunch of inverters (NOT gate) strung together. Not long ago, slashdot had an article about a transparent ring oscillator from Oregon State Univ. Again, this was done as a stepping stone from discovering an entirely new semiconductor (this is NOT silicon, people) to making a useful device.
A carbon nanotube (CNT) is a rolled graphene plane (ie, carbon atoms in a hexagonal structure). So of course all current will be on the 'outside' of the tube, as the tube itself really only consists of the outside.
IBM was probaby comparing single-wall nanotubes to multi-wall nanotubes. Multiwall nanotubes are composites of a bunch of concentric single-wall nanotubes. Their better results in the single-wall variety are probably due to less scattering between the graphene planes. A single CNT has a well-defined crystal structure, and is actually quite interesting. The graphene plane itself is sometimes referred to as a 'zero-bandgap insulator', where the density of states linearly goes to zero at the fermi energy (unlike an insulator or semiconductor which has a energy gap at the fermi energy, and hence cannot conduct decently like a metal).
However through changes to the nanotube material, the performance of the nanotube may be impreved.
They probably can get to higher frequencies. I mean, even the vibrational phonon modes of a single nanotube can be in the GHz range or higher (ie, these are the various modes of vibration that the nanotube would exhibit if you struck it, kind of like a wind chime). I don't know specifics, but I don't see why the nanotube couldn't support electronic channels with bandwidths into the GHz or even higher as well.
Although nanotubes do have interesting characteristics different from typical metals and semiconductors. Ie, the electron-phonon interaction goes as 1/T, instead of 1/T^5 (where T is temperature). So at low temperatures there might be useful ways to couple electronic channels to vibrational modes not possible in conventional materials. Or vice versa, the phonon modes might more easily kill off electronic signals. There's alot of interesting work being done with nanotubes, and I'm sure some clever physicists and engineers will exploit these characteristics well in the near future.
A 5-stage ring oscillator is the hardware equivalent of a program that displays 'Hello World!'
OK here's the explanation in 1337:
Carbon nanotubes = t3h w00t
CMOS = reality
Ring oscillator = first tests to integrate t3h w00t into reality
It means that before this, nanotubes and nanotube transistors were only tested in the lab, using microscopic clamps, cables, probes, etc. But this is the first time that a carbon nanotube can be integrated into a working CMOS chip (a small step for chips, a giant leap for mankind). Once CMOS manufacturing can be adjusted for carbon nanotubes, we'll be able to manufacture nanotube memory, nanotube chipsets, and finally, nanotube CPU's!
This is what i've been waiting for since i ever heard about nanotube transistors (however, i think that using graphene sheets instead of nanotubes will be much more effective).
Lets see if this helps. Some people were confused...
A ring oscillator is a device for making square waves. It uses a common component, a NOT gate. In digital logic, there are two levels, high and low (or 1 and 0, respectivly). High is usually, as far as I have seen, +5 volts, while low is 0 volts (ground).
A NOT gate simply inverts the input. If the value is 1, it outputs 0. If the value is 0, it outputs 1. If the value is somewhere between the two, it will choose one state or the other based on some threshold voltage.
Changing output is not instantaneous. How much time it takes, I don't know. However, it is very fast.
I was going to draw a schematic, but I gave up on appeasing the lameness filter. So, we will use the power of imagination! Imagine one of these NOT gates hooked up to itself. It will switch on and off at a terrific rate. Put a wire on the output, and you have a square wave! Want it slower? Take another two NOT gates, and put them in the loop, so that the first one goes to the second goes to the third. Slower? Another two. If the number of NOT gates was even, the inverted signal would be uninverted by the next NOT gate, which is not what we want.
For more control, one can use a capacitor in a certain arrangment (I'm not looking through my notes). It will take a while to charge and discharge, acting as a delay. Just don't read its voltage as the signal, or you will get a dropping bit, then a rising bit, rather than a nice clean square wave.
Quite useful devices. I hope this clarifies things.
I have freaks! I did something right...
It's the same at the Niels Bohr Institute. 'Nano' definitely has the hottest chicks. They are almost in the same league as the biochemistry department!
All nanotubes are made up of this graphene plane.
Actually, you can make nanotubes out of other materials besides carbon. Metallic nanotubes, for example, will have different crystal structures than the graphene hexagon.
A tube with 100 atoms will have 100 distinct oscillating modes.
No, it will have 300, one for each degree of freedom. However, three of these will be translational modes, which are not phonon modes, so really there will be 297 distinct phonon branches. In addition you should distinguish between the number of atoms in a Carbon Nanotube, and the number of atoms in its unit cell. A unit cell may have 100 atoms, but the entire nanotube can be made of 1000s of unit cells. The number of atoms in the unit cell is the important number for calculating phonons.