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Director: Pertti Hakonen
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LT » Nano Group » Carbon nanotubes » Early works on nanotube transistors

Early works on nanotube transistors

Ultrasensitive SET

Our first nanotube device was a SET made of an arc-discharge-grown MWNT using AFM manipulation (material from P. Bernier, University of Montpellier).

In this device, we saw single electron charging effects via gate modulation. The results imply this MWNT to be semiconducting with a gap of 15 meV. The observed Coulomb staircase structure agrees with asymmetry of the tunnel junctions. The Coulomb energy of the island was 23 K.

We have shown that it is possible to construct low-noise single-electron transistors (SETs) using free-standing multiwalled carbon nanotubes. The 1/f^α-noise of our devices, 6.10^-6e/√Hz at 45 Hz, is close in the performance to the best metallic SETs of today.

First MWNT SET made by moving an arc-discharge-grown tube on top of prefabricated gold leads: the left end is on top of the lead while the right end touches the lead from aside.	AFM picture of the free-standing MWNT device, on which the record charge sensitivity was measured. The cross-sectional view is shown below; the dimensions are in nanometers.
Scheme of the free-standing MWNT device, on which the record charge sensitivity was measured.	Current noise in measured at minimum (lower) and maximum gain (upper trace). The right axis, obtained by scaling with the inverse of charge sensitivity 1/gch = 0.25 e/nA, gives the equivalent charge noise Dq for the upper trace.

Cross tube SET

The Radio-frequency single electron transistor (RF-SET) is the fastest and most sensitive electrometer known today. Many schemes proposed for sensitive measurement applications have invoked the promise of the RF-SET for fast and ultra-sensitive charge detection. These include Qubits based on nuclear spins in silicon, charged particle detectors, quantum nanomechanical oscillations and single terahertz photon counters. It is one of the only tools for detecting single electron charges at the nanometer scale and with gigahertz band-width.

In collaboration with the Chalmers and Yale groups, we have made theoretical analysis and experiments to estimate the charge sensitivity of a radio frequency single-electron transistor. The theoretical prediction is based on a model which includes equivalent circuits for all the components of the measurement system. Low-noise first-stage amplifier was integrated in the analysis and the noise power wave formalism was employed in the analysis of the aluminum single-electron transistor test system.

Sequence of AFM pictures taken during the manufacturing of the nanotube cross.

A SET device made using two crossing arc-discharge-grown MWNTs. The charge sensitivity of this device was measured to be 6.10-4e/√Hz.

Current of the nanotube-SET as a function of the gate voltage Vg and the bias voltage Ub. The Coulomb blockade is clearly seen in the rhombic regions in the center.

Related publications

• Manufacture of single electron transistors using AFM manipulation on multiwalled carbon nanotubes

L. Roschier, R. Tarkiainen, M. Ahlskog, M.A. Paalanen, P.J. Hakonen

Microelectron. Eng. 61-2, 687 (2002)

• Multiwalled carbon nanotubes as building blocks in nanoelectronics

M. Ahlskog, P.J. Hakonen, M.A. Paalanen, L. Roschier, R. Tarkiainen

J. Low Temp. Phys. 124, 335 (2001)

• Multiwalled carbon nanotubes as ultrasensitive electrometers

L. Roschier, R. Tarkiainen, M. Ahlskog, M.A. Paalanen, P.J. Hakonen

Appl. Phys. Lett. 78, 3295 (2001)

• Single-electron transistor made of two crossing multiwalled carbon nanotubes and its noise properties

M. Ahlskog, R. Tarkiainen, L. Roschier, and P.J. Hakonen

Appl. Phys. Lett. 77, 4037 (2000)

• Single-electron transistor made of multiwalled carbon nanotube using scanning probe manipulation

L. Roschier, J.S. Penttilä, M. Martin, P.J. Hakonen, M.A. Paalanen, U. Tapper, E.I. Kauppinen, C. Journet,and P. Bernier

Appl. Phys. Lett. 75, 728 (1999)