Single Atom Transistor

It is the promise of this future technology that makes this present development so exciting. Simulations of the atomic transistor to model its behavior were conducted at Purdue using nanoHUB technology, an online community resource site for researchers in computational nanotechnology. Gerhard Klimeck, who directed the Purdue group that ran the simulations, says this is an important development because it shows how small electronic components can be engineered. The latest Intel chip, the "Sandy Bridge," uses a manufacturing process to place 2.

A single phosphorus atom, by comparison, is just 0. The single-atom transistor does have one serious limitation: It must be kept very cold, at least as cold as liquid nitrogen, or minus degrees Fahrenheit minus Celsius. For this atom to act like a metal you have to contain the electrons to the channel. But this is a fundamental question for this technology.

The structure even has markers that allow researchers to attach contacts and apply a voltage, says Martin Fuechsle, a researcher at the University of New South Wales and lead author on the journal paper. Simmons says this control is the key step in making a single-atom device. Some scientists, however, have doubts that such a device can ever be built. The technique we have developed is potentially scalable, using the same materials as the silicon industry, but more time is needed to realize this goal.

This will lead to many more discoveries. The source-drain conductance GSD of the atomic switch red curves is directly controlled by the gate potential UG blue curves. Figure 4 shows a sequence of reproducible switching events between an insulation "off-state" and a quantized conducting "on-state" at 1 G0 , where the quantum conductance red curves of the switch is controlled by the gate potential blue curves , as commonly observed in transistors.

As calculations have shown [10], for atomic-scale silver contacts a quantized conducting "on-state" of 1 G0 corresponds to a single-atom contact. When we set the gate potential to an intermediate "hold" level between the "on" and the "off" potentials, the currently existing state of the atomic switch remains stable, and no further switching takes place. This is demonstrated in Fig. Thus, the switch can be reproducibly operated by the use of three values of the gate potential for "switching on", "switching off" and "hold".

These results give clear evidence of a hysteresis when switching between the two quantized states of the switch. It can be explained by an energy barrier which has to be overcome when performing the structural changes within the contact when switching from the conducting to the non-conducting state of the switch and vice versa. The results indicate that switching occurs by a reversibly rearrangement of the contacting group of atoms between two different stable configurations with a potential barrier between them.

For silver the observed quantum conductance levels appear to coincide with integer multiples of the conductance quantum [1,10]. The observed integer conductance levels of the switch are determined by the available bistable junction conformations, similar to the observation of preferential atomic configurations in metallic clusters corresponding to "magic numbers" [12].

By snapping into 'magic' bistable conformations, such energetically preferred junctions configurations are mechanically and thermally stable at room temperature, and they are reproducibly retained even during long sequences of switching cycles. Multilevel switching Reproducible switching in the above cases was always performed by opening and closing a quantum point contact, i.

However, it was not clear if this kind of gate-electrode controlled switching is also possible between two different conducting states of one and the same contact. Such kind of switching would involve two different stable contact configurations on the atomic scale, between which reversible switching would occur even without ever breaking the contact. Such multi-level logics and storage devices on the atomic scale would be of great interest as they allow a more efficient data storage and processing with a smaller number of logical gates.

By developing a modified procedure of fabrication, a multi-level atomic quantum transistor was obtained, allowing the gate-controlled switching between different conducting states. Instead of setting the lower threshold where the dissolution process is stopped by the computer, to a value near 0 Go, the lower threshold was set at a value above the desired quantized conductance of the lower of the two "on-state" levels [13].

Figure 6 demonstrates the operation of such a twolevel transistor: A controlled change of the gate potential UG leads to a controlled switching of the conductance of the quantum point contact between two different quantized conducting states, exhibiting conductance levels of 1 G0 and 3 G0, respectively.


Atomarer Transistor