Fabrication of a single-electron transistor
By using the CILO process in combination with AFM oxidation, we fabricated a Coulomb island separated by two tunneling barriers from large-area contacts. Using the doped Si substrate underneath the metal film as gate electrode, this device can be employed as a single-electron transistor.
The current-voltage curve of a smaller device with an island diameter of less than 20 nm (see inset) exhibits several equidistant steps as a consequence of Coulomb blockade at room temperature
The IBM scientists will now use the ring oscillator to test improved carbon nanotube transistors and circuits, and to gauge their performance in complete chip designs.
IBM researchers built a complete electronic circuit around a single-walled carbon nanotube – an object which is 50,000 times thinner than a human hair. This is the first complex integrated circuit implementation that is entirely done on a single molecule.
Depending on the synthesis process, a single-walled carbon nanotube has a diameter in the range of nanometers. This extremely small size naturally lends itself to the miniaturization goal of current semiconductor industry. Also, owing to the small nanotube diameter, carbon nanotubes are found to possess unique physical properties that are beneficial for high speed and low power electronics applications.
Once properly wired-up, the individual carbon nanotube functions as an entire circuit - a molecular ring oscillator. The monitored output signal is of ac type while the input uses a low power dc voltage. The architecture that has been employed makes use of the unique carbon nanotube properties while it ensures at the same time compatibility with well established circuit concepts.
Size comparison between our single nanotube ring oscillator circuit and a human's hair.
A close-up view of the 5-stage CMOS type nanotube ring oscillator. The upper right inset shows the nanotube itself with a diameter of ~2nm.
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