Carbon nanotube RF-SETs
Multiwalled carbon nanotube RFSETs
Single electron transistors (SET) are the most sensitive electrometer ever made . However, these devices are limited by very small bandwidth (few kHz) for charge detection. One way to circumvent such problem has been proposed by R.J. Schoelkopf et al. : they used a reflected carrier wave from the impedance transformer circuit and the SET. The variation of the island charge changes the impedance of the SET. Consequently, the amplitude of the reflected wave is modulated according to the SET impedance changes. The optimal charge sensitivity is achieved when the SET and the wave impedance of the transmission line are perfectly matched. The SET bandwidth is limited by the loaded Q-factor of the impedance transformer. The theoretical maximum bandwidth can be found using the Bode-Fano criterion . The best sensitivity have been obtained using superconducting SETs (also called Cooper pair box)made of Al-AlOx, approaching the shot noise limit of h/2π . For normal state SET the theoretical value has been predicted to be around 1.4h/2π . At liquid helium temperature, the best charge sensitivity so far has been measured of δq=1.9*10-6e/√Hz . Because of their large charging energy and their small capacitance, carbon nanotubes are very promising for RF-SETs. Early measurements with multi walled carbon nanotubes have demonstrated great potential .
 M.H. Devoret and R.J. Schoelkopf, Nature 406, 1039 (2000).
 R.J. Schoelkopf, P. Wahlgren, A.A. Kozhevnikov, P. Delsing, and D.E. Prober, Science 280, 1238 (1998).
 D.M. Pozar, Microwave engineering, Addison-Wesley, New York, 1st edition (1990).
 A. Aasime, D. Gunnarsson, K. Bladh, P. Delsing, and R.J. Schoelkopf Appl. Phys. Lett. 79, 4039 (2001).
 A.N. Korotkov and M.A. Paalanen, Appl. Phys. Lett. 74, 4052 (1999).
 H. Brenning, S. Kafanov, T. Duty, S. Kubatkin and P. Delsing, J. Appl. Phys. 100, 114321 (2006).
 L. Roschier, M. Sillanpää, W. Taihong, M. Ahlskog, S. Iijima, and P. Hakonen, J. Low Temperature Phys. 136, 465 (2004).
Singlewalled carbon nanotube RFSETs
Here we have measured an RF-SET based on a single walled nanotube in the strong tunneling regime at T=4.2 K: we showed the sensitivity obtained is comparable to the one measured by H. Brenning et al., J. Appl. Phys. 100, 114321 (2006), but with a much better gain*bandwidth (one order of magnitude larger). This study has been done in collaboration with Søren Andresen from the Niels Bohr Institute, Copenhagen, within the CARDEQ project.
- Highly sensitive and broadband carbon nanotube radio-frequency single-electron transistor
S.E.S. Andresen, F. Wu, R. Danneau, D. Gunnarsson, and P.J. Hakonen
- Carbon nanotube radio-frequency single-electron transistor
L. Roschier, M.A. Sillanpää, T.H. Wang, M. Ahlskog, S. Iijima, and P.J. Hakonen
J. Low Temp. Phys. 136, 465 (2004)