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- Brenning, Henrik, 1972
(författare)
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Fabrication and Characterization of Aluminum Single Electron Transistors for Scanning Probes
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of the work presented in this thesis was to fabricatescanning single electron transistor probes that operate at pumped liquid heliumtemperatures. This required single electron transistors (SETs) with low resistance (R_) and relatively high charging energy (E_C), and the technology tointegrate SETs onto probes.By reducing the oxygen pressure during the in situ oxidation of a 2-angleevaporation, the specific tunnel resistance of aluminum tunnel junctions wasreduced. SETs with charging energies up to 20K*kB and with a typicalresistance of 100 kOhm were fabricated. These SETs were DC- measured both at4.2K and at 90 mK. The inverse resistance-capacitance (RC) product was ashigh as 42 GHz, and this was obtained without increasing the noise above that,typical for aluminum SETs.SETs with even lower RC product, corresponding to a cut of frequency of120 GHz, were produced and measured with RF methods. These measurementsyielded the highest reported charge sensitivity of any SETs, At 40mK we ob-tained, 0.9 e/Sqrt(Hz) in the superconducting state and 1.0 e/Sqrt(Hz) in the normalstate. RF operation at 4.2K was demonstrated with this sample, also with avery good charge sensitivity: 1:9 ¹e=pHz.To further characterize this SET, we measured the 1/f noise up to 10 MHz,and showed that one strong resistance °uctuator was situated in one of thetunnel junctions. In a second noise characterization, we measured the shotnoise of this device and extracted the Fano factor at small and large voltagebiases.In the last part of this work, we developed a general method to fabricatesharp cantilevers and perform e-beam lithography, with dimensions down to30nm at the tip of these cantilevers. The alignment precision was better than30 nm between the cantilever structures and the lithographic pattern. Withthis method, we were able to mass produce SETs at the corners of cantilevers.These SETs were DC characterized at 100mK and at pumped liquid heliumtemperatures (T = 1.3 and 2 K), and had typical parameters of R = 100 kOhm andE_C = 3.5K/k_B. We furthermore integrated one of these cantilevers on a tuningfork AFM, and performed a proof of concept AFM scan. The RMS height noiseof this scan was ~ 1 nm, which indicates that very small scanning heights, andhence high lateral resolution, should be possible with this combined probe.
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- Kafanov, Serguei, 1977, et al.
(författare)
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Charge noise in single-electron transistors and charge qubits may be caused by metallic grains
- 2008
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969. ; 78:12, s. 125411-
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Tidskriftsartikel (refereegranskat)abstract
- We report on measurements of low-frequency noise in a single-electron transistor (SET) from a few hertz up to 10 MHz. Measurements were done for different bias and gate voltages, which allow us to separate noise contributions from different noise sources. We find a 1/f noise spectrum with two Lorentzians superimposed. The cut-off frequency of one of the Lorentzians varies systematically with the potential of the SET island. Our data is consistent with two single-charge fluctuators situated close to the tunnel barrier. We suggest that these are due to random charging of aluminum grains, each acting as a single-electron box with tunnel coupling to one of the leads and capacitively coupled to the SET island. We are able to fit the data to our model and extract parameters for the fluctuators.
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