0000000000054536
AUTHOR
P. J. Koppinen
Discrete saturation thickness and anomalous potential height of native ultrathin aluminum oxide tunnel barriers
We have investigated planar metal - insulator - metal tunnel junctions with aluminum oxide as dielectricum. These oxide barriers were grown on an aluminum electrode in pure oxygen at room temperature till saturation. We observed discrete barrier widths separated by \Delta s \approx 0.38 nm, corresponding to the addition of one layer of oxygen atoms. The minimum thickness of s_0 \approx 0.54 nm is due to a double layer of oxygen. We found a strong and systematic dependence of the barrier height \Phi_0 on the thickness s like \Phi_0 \approx 2.5 eV / s^2(nm), which nearly coincides with the kinetic electron energy E = h^2/2ms^2 for which the deBroglie wavelength matches the width of the barrie…
Strain sensing with sub-micron sized Al-AlOx-Al tunnel junctions
We demonstrate a local strain sensing method for nanostructures based on metallic Al tunnel junctions with AlOx barriers. The junctions were fabricated on top of a thin silicon nitride membrane, which was actuated with an AFM tip attached to a stiff cantilever. A large relative change in the tunneling resistance in response to the applied strain (gauge factor) was observed, up to a value 37. This facilitates local static strain variation measurements down to ~10^{-7}.
Reduction of low-frequency 1/f noise in Al-AlOx-Al tunnel junctions by thermal annealing
We report that annealing Al-AlOx-Al tunnel junctions in a vacuum chamber at temperature of 400C reduces the characteristic 1/f noise in the junctions, in some cases by an order of magnitude. Both ultra high vacuum and high vacuum fabricated samples demonstrated a significant reduction in the 1/f noise level. Temperature dependence of the noise was studied between 4.2 and 340 Kelvin, with a linear dependence below 100 K, but a faster increase above. The results are consistent with a model where the density of charge trapping two level-systems within the tunneling barrier is reduced by the annealing process.
Phonon Cooling of Nanomechanical Beams with Tunnel Junctions
We demonstrate electronic cooling of 1D phonon modes in suspended nanowires for the first time, using normal-metal-insulator-superconductor (N-I-S) tunnel junctions. Simultaneous cooling of both electrons and phonons to a common temperature was achieved. In comparison with nonsuspended devices, better cooling performance is achieved in the whole operating range of bath temperatures between 0.1-0.7 K. The observed low-temperature thermal transport characteristics are consistent with scattering of ballistic phonons at the nanowire-bulk contact as being the mechanism limiting thermal transport. At the lowest bath temperature of the experiment approximately 100 mK, both phonons and electrons in…
Complete stabilization and improvement of the characteristics of tunnel junctions by thermal annealing
We have observed that submicron sized Al--AlO{$_x$}--Al tunnel junctions can be stabilized completely by annealing them in vacuum at temperatures between $350^{\circ}$C and $450^{\circ}$C. In addition, low temperature characterization of the samples after the annealing treatment showed a marked improvement of the tunneling characteristics due to disappearance of unwanted resonances in the current. Charging energy, tunneling resistance, barrier thickness and height all increase after the treatment. The superconducting gap is not affected, but supercurrent is reduced in accordance with the increase of tunneling resistance.