Thesis presented July 13, 2012

Abstract:
Future of the next camera on board space observatories implies a major enhancement in number of pixels and a very low operative temperature (below 0.1 K). In this evolution, the large number of output wires from the cool detector is often responsible of the most important thermal load onto the cold bath (cryostat). In this context, the thermal insulation between the different detection circuits is the bottleneck for these cameras. An innovative technological component, protected by a patent, has been developed to tackle this problem. This device has both an excellent electrical resistivity and a very high thermal resistivity. The proposed solution is a stack of thin superconducting layers at electrical interconnections. The thermal resistance at each interface relies on the elastic properties of the materials used, the quality of the interfaces and temperature. The AMM model used in conjunction with the measured material characteristics allows a theorical estimation of the thermal resistance per interface. The measurements under taken with superconducting connections with very high thermal resistivity are very well described by this AMM model. We have measured thermal resistances as high as 3.3 10⁵ K/W @ 200 mK for a multilayer of 62 interfaces built with titaniun nitride and niobium alternatively on a 16 mm² array. In the conditions foreseen for a 4000 micro-calorimeters camera operating at 50 mK in X-rays, this multilayer technique should allow a thermal load onto the cold bath that is much lower that 1 mW for more than 8000 contacts.

Keywords:
Thermal resistance, Supersonductors, Phonon, Multilayer, AMM model, Titanium nitride, Niobium

On-line thesis.