Abstract
In this paper we report a study of the effect of vacuum annealing at 400°C on the properties of normal metal-insulator-superconductor (NIS) tunnel junctions, with manganese doped aluminium (Al:Mn) as the normal metal, aluminum as the superconductor and amorphous aluminum oxide as the tunneling barrier (Al:Mn-AlOx-Al). The annealing treatment improves the stability of the junctions, increases their tunneling resistance and does not have a negative impact on the low-temperature current-voltage characteristics. The measured 1/f resistance noise of the junctions also changes after annealing, in the best case decreasing by over an order of magnitude. All these observations show that annealing is a viable route to improve NIS junction devices after the sample has been fabricated.
Highlights
Superconducting tunnel junctions are important components for applications in quantum information processing,[1] metrological applications,[2] solid state coolers,[3] ultrasensitive radiation detection[4] and low-temperature thermometry.[5]
In single electron transistor (SET) devices and charge qubits, the 1 / f noise is typically dominated by charge noise that may originate from the surroundings of the junctions, and the barrier.[21,22,23,24,25]
The question we decided to address in this paper is: How does the vacuum annealing treatment affect the properties of normal metal-insulator-superconductor (NIS) junctions? If stability, sub-gap current or 1 / f noise can be improved, one could perhaps improve the performance of hybrid single electron SINIS turnstiles,[2,26] SINIS thermometers and coolers and NIS-junction based radiation detection.[27,28,29]
Summary
Superconducting tunnel junctions are important components for applications in quantum information processing,[1] metrological applications,[2] solid state coolers,[3] ultrasensitive radiation detection[4] and low-temperature thermometry.[5]. Many fabrication protocols do not automatically guarantee this, but special measures such as vacuum annealing,[7] agressive cleaning[8] and multistep oxidation[9] have been shown to improve the stability of Al-AlOx-Al tunnel junctions Another quite general problem is that many electronic devices exhibit excess non-equilibrium noise which typically has a frequency spectrum close to 1 / f.10,11. Many other applications require NIS (normal metal-insulator- superconductor) junctions, where one of the electrodes is in the normal state while the other is superconducting This means that the junctions have to be fabricated using two different materials, with most common combinations being Cu-AlOx-Al, AuPd-AlOx-Al (AuPd alloy) and Al:Mn-AlOx-Al (Al with Mn impurities).[2,5] For the above reason, the question we decided to address in this paper is: How does the vacuum annealing treatment affect the properties of NIS junctions? A non-uniform manganese profile shows a reorganization after annealing
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