Logic Circuit
IBM Scientists Build World's First Single-Molecule Computer Circuit
IBM's Intra-Molecular Logic-Performing Computer Circuit
(a) Atomic Force Microscope image showing the design of an intra-molecular logic gate. A single carbon nanotube (shaded in blue) is positioned over gold electrodes to produce two p-type carbon nanotube field-effect transistors in series. The device is covered by an insulated layer (called PMMA) and a window is opened by e-beam lithography to expose part of the nanotube. Potassium is then evaporated through this window to convert the exposed p-type nanotube transistor into an n-type nanotube transistor, while the other nanotube transistor remains p-type. (b) Characteristics of the resulting intra-molecular voltage inverter. Open red circles are raw data for five different measurements on the same device (V=±2V). The blue line is the average of these five measurements. The thin straight line corresponds to an output/input gain of one.
IBM's Inter-Molecular Logic Circuit
Fabrication of a voltage inverter (“NOT” logic gate ) using two nanotube field-effect transistors. Initially the two nanotube transistors are p-type. One of the them is protected by an insulating layer, the other is not.
(a) Placing the nanotubes in a vacuum converts the p-type nanotube transistors to n-type.
(b) The two CNTFETs are then exposed to oxygen (10-3 Torr of oxygen for 3 minutes). The unprotected n-type nanotube transistor (black curve) converts back to the original p-type, while the protected nanotube transistor (red curve) remains n-type.
(c) The two complementary (p-type and n-type) carbon nanotube transistors are wired as shown in the schematic.
(d) characteristics of the resulting inter-molecular inverter (V=1.5 V).
Electrical characteristics of n-type nanotube FETs made by:
(a) annealing (heating) the device in vacuum at 700 Kelvin for 10 minutes.
(b) doping with potassium.
The curves are obtained at different values of VDS starting for (a) from 300 mV, step size 200 mV and for (b) at 200 mV, step size 200 mV.
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