Cold-Electron Bolometers

Abstract

This thesis concerns the fabrication of Cold-Electron Bolometers (CEBs) with shadow angle evaporation technique, suitable for measuring the Cosmic Microwave Background Radiation as a part of the BOOMERanG project. We have studied two possible improvements of the absorber. Firstly, we have decreased the thickness of the aluminium layer at the top of the absorber (7, 10, 15, 20 nm) in order to see if a smaller absorber volume would improve the bolometer. We have seen that bolometers with arrays of Superconductor-Insulator-Normal Metal (SIN) junctions exhibit improved characteristics for thinner absorbers. Estimates show that with these changes, the CEBs can soon meet with the noise requirements for the BOOMERanG project. We have also confirmed that larger arrays are saturated at a higher powerload, as it is distributed among the absorbers. Secondly, we varied the thickness of the chromium layer at the bottom of the absorber (0.1,0.2,0.3,0.5 nm) to see if we could achieve a bolometer with Superconductor-Insulator-Weak Superconductor (SIS’) junctions. We found that the thinnest chromium layer did not fully suppress the superconducting properties of aluminium, but with the current equipment of the Bolometer Group at Chalmers it is probably impossible to repeatedly reproduce a weak superconductor with a specific critical temperature using this method.