The Single-Atom Transistor: Perspective for Quantum Electronics at Room Temperature
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Transcript: English(auto-generated)
00:18
I'm professor Thomas Schimmel from the Karlsruhe Institute of Technology.
00:22
Here at the Institute of Applied Physics and the Institute of Nanotechnology in my group we're doing research on the smallest scale electronics. Smallest scale means doing electronics with one individual atom. You may ask yourself, is it much electrical current you can put through one individual
00:44
atom? And the answer is amazing. You can easily have one micro-am of current going through one individual atom, meaning that you have more than 6,000 billion electrons going one at a time through one atom in one
01:06
second. More than 6,000 billion electrons in one second through one atom, that's an electrical current you can technologically use. Well, basically here you see how such an atomic transistor is working.
01:20
You have a contact from left to right made of metal, you have the metallic contact on the left, here the symbols of the individual atoms on the right, but no current is flowing because there's a tiny single atom time meter gap between left and right. Now you could think of taking this atom and moving it to that position, in this
01:42
case the electrical current can flow, the gap is closed, can go from left to right, the circuit is closed. So by the movement of one single atom out in or out of the contact, you can close, open, close the electrical contact. So you have a single atom switch and basically you have demonstrated the function of a transistor
02:08
on the atomic scale. We can just call the left-hand electrode source, we could call the right-hand electrode grain, we have a control electrode which controls the position of the central atom,
02:22
flipping it in and out, and in this way we have a fairly conventional transistor if we look at it at a black box which has a certain functionality. At a second glance it's a very interesting transistor, a non-conventional transistor in different respects. It's for the first time a transistor, a single atom transistor, operating by the controlled
02:44
moving in and out of a single atom and that at room temperature at ambient conditions. It's a transistor working with quantum mechanics, the conductance between left and right having not any value but a value quantized and controlled by the rules of quantum mechanics.
03:04
Only certain logical levels are possible, which are multiples of 2E2 over H, E being the electron charge and H Planck's quantum. It's a quantum transistor on the atomic scale and it's interesting also from a third respect. It's a first demonstration of an all-metal transistor which is semiconductor free.
03:23
There's no semiconductor in it. The operation voltages possible with this transistor are in the millivolt range allowing ultra-low energy consumption transistors. We're getting rid of the semiconductor in the transistor. How could we fabricate such a device?
03:41
That's amazingly simple. We can just use a glass slide or a silicon wafer on top of which we make two metallic electrodes for example of gold which have a gap between them of only 15 nanometers. That's something you can do with fairly conventional micro-nano fabrication techniques.
04:04
Then between these two gold electrodes you deposit silver nanocrystals from an electrolyte solution from a metal salt solution. You deposit from the right and from the left two silver nanocrystals computer controlled atom by atom until these two contacts meet in one single atom.
04:26
That can be very easily detected because at the point the two contacts meet in one atom the conductance from left to right is jumping upwards. The computer can easily detect it and stop the further deposition and so you have a single
04:42
atom contact. Well how does this work practically? What does the experiment look like? Please follow me to the lab. So here we are in the laboratory of Dr. Feng Xingxie who is fabricating the atomic transistor.
05:03
Dr. Xie just is preparing the sample here. Well I would suggest let's just finish the sample and put it into the setup so that we could start the next measurement. Here on the sample that's a conventional glass chip on which of course very much smaller
05:26
than what one could see. The junction for the atomic transistor is fabricated. This tiny junction is now inserted into the sample holder and here we see the setup
05:40
which is a fairly simple setup, computer controlled as you see and there's no large fabrication facility needed. We just have a computer program and a little bit of electrochemistry making the single atom transistor.
06:01
Now the sample is put into the sample holder, into the electrolyte for fabrication, it's now contacted with four leads and well then I think let's start the experiment.
06:21
And you see here the control voltage in red and you see the switching of the atomic transistor. You see that the scale is 1.0, 1.0 means one quantum mechanical conductance quantum, two e square over h, h being Planck's quantum, so you have a quantized switching
06:42
of the current on when the atom is flipping in and out of when the atom is flipping out. This flipping in and out of the atom is controlled by this gate voltage which we see on the left hand side. So we see the transistor operating. We can even do a different thing.
07:00
The current coming out of the transistor can be directly fed into an electronic circuit, a conventional electronic circuit which you can buy for two euros and which is controlling a light bulb. So we have a halogen lamp here. We go now with the current coming out of the atomic transistor into the halogen lamp
07:22
and you see that the current coming from one atom is now controlling the lamp. So it's one microamp, the current coming out of one atom is enough to control conventional electronics. Of course, it's still, these are the very first steps into a very new technology, into
07:48
a very new field, but there are interesting perspectives in different ways and another point is that in principle you can go to ultrahigh frequencies. We do not yet do it, but in principle the rate at which a single atom can be moved
08:08
up and down is extremely high, higher than what we could do with conventional electronics where we always have capacitances, we have to charge. Here we have one atom which can basically be flipped at the oscillation frequencies
08:25
of atoms in a solid. So the high frequency limit which we not yet explore is very far off, so the technology limits give great perspectives also in the direction of high frequency devices.