Bandwidth coverage of niobium based superconducting tunnel devices
C.F.J. Lodewijk
T.M. Klapwijk – Promotor
More Info
expand_more
Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons.
Abstract
The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical observatory that is being built on a 5000 m altitude plateau in Chile to perform heterodyne measurements in the frequency range of 30 to 950 GHz. These measurements will reveal the presence of characteristic molecules that tell us more about the evolution of the early universe and the formation of stars and planetary systems. Because of the limited atmospherical transmission of radiation at these frequencies, ALMA is divided into 10 frequency bands with a sufficiently high transmission. This thesis describes the research that has been done to develop superconductor - insulator - superconductor (SIS) tunneljunctions as detectors for Band 9 of ALMA (602 - 720 GHz). To realize these devices, a tuning circuit has been developed that optimizes the coupling of electromagnetic radiation from the antenna to the SIS junction. Further, a new method has been developed to create SIS junctions with aluminum nitride (AlN) as the insulating material. This method uses a remote plasma from an inductively coupled plasma source. Junctions that have been grown with this new method show a much better uniformity in transmissivity of the tunneling barrier at high critical current densities. Using the new method, SIS devices with AlN tunnel barriers have been developed that have a record low noise temperature over the full bandwidth of Band 9.