Développement de Jonctions Supraconductrices à Effet Tunnel pour le comptage de photons en astronomie

Corentin Jorel 1
1 électronique
LAOG - Laboratoire d'Astrophysique de Grenoble
Abstract : This work describes the development of S/Al-AlOx-Al/S Superconducting Tunnel Junctions (STJ) to count photons for astronomical applications in the near-infrared. The incoming light energy is converted into excited charges in a superconducting layer (S, either Nb or Ta) with a population proportional to the deposited energy. The photon energy can thus be evaluated by integrating the tunnel current induced in a voltage biased junction at a very low temperature (100 mK). The performance of STJs for light detection is discussed in the first chapter and compared with the best performances obtained with other techniques based on either superconductors (Hot Electron Bolometers, Transiting Edge Sensors) or semiconductors (Avalanche Photodiodes, Photomultipliers, CCDs). At the beginning of the thesis, a previous manufacturing process made it possible to obtain good quality Nb based junctions and preliminary results for photon counting. The objective of the thesis was to replace Nb as absorber with Ta, an intrinsically more sensitive material, and secondly to develop a new and more efficient manufacturing process. We first focused on the optimization of the Tantalum thin film quality. Structural analysis showed that these films can be grown epitaxially by magnetron sputtering onto an R-plane sapphire substrate heated to 600°C and covered by a thin Nb buffer layer. Electrical transport measurement from room to low temperatures gave excellent Relative Resistive Ratios of about 50 corresponding to mean free path of the order of 100 nm. Then, we conceived an original manufacturing process batch on 3 inch diameter sapphire substrate with five mask levels. These masks made it possible to produce single pixel STJs of different sizes (from 25*25 to 50*50 square microns) and shapes (some of the devices are rhombus- and others sine-shaped). We also produced multiple junctions onto a common absorber as well as 9-pixel arrays. Thanks to the development of this process we obtained a very large percentage of quality junctions (>90%) with excellent measured normal resistances of a few micro-ohm cm^2 and low leakage currents of the order of one nA. Finally, we have demonstrated the photon counting capability of these devices at the border of visible and near-infrared (0.78 micron) wavelengths. Better energy resolution can even be achieved by further improvements in the experimental set-up, showing that such detectors are very promising for low light level applications in ground based astronomy (optical or near-infrared) or alternatively for cryptography and telecommunication applications at 1,55 micron.
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Submitted on : Tuesday, August 16, 2005 - 5:14:41 PM
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Corentin Jorel. Développement de Jonctions Supraconductrices à Effet Tunnel pour le comptage de photons en astronomie. Micro et nanotechnologies/Microélectronique. Institut National Polytechnique de Grenoble - INPG, 2004. Français. 〈tel-00009943〉

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