Intrinsic Josephson Microwave Phase Shifter
Timothy A. Wootton
Phase shifters are a vital part of communication systems, and research into superconducting electronic devices has highlighted the possible application of Josephson junctions in this field of research. Intrinsic Josephson junctions (IJJs) are created by the high-density atomic-scale superconducting/insulator layering found within high temperature superconductors, such as Tl2Ba2CaCu2O8. This means a large number of series junctions are able to be created in relatively small dimensions in comparison to extrinsic devices limited in size by fabrication techniques. By designing IJJ tracks with large numbers of junctions in series, the phase shift from each individual junction sums to produce significant measurable phase tunability. I have studied the characteristics of IJJ tracks fabricated in Tl2Ba2CaCu2O8 to investigate the their use as microwave phase shifters. This involved determining the optimum track dimensions to ensure true Josephson behaviour of the IJJs by measuring the current-voltage characteristics at 4.2K. I have derived the equations governing the phase bias relationship, used these to simulate the expected junction characteristics based on the track parameters. These were then compared with the measured results and discussed in the context of other research in the field. Based on the phase tunability measured in the Tl2Ba2CaCu2O8 tracks, I then proceed to investigate the possible use of the coplanar IJJ transmission line as a parametric amplifier. The results presented highlight a small region of gain coupled to a geometric resonance, however this is not due to any parametric effect. Further research in this area is required to excite parametric amplification from these devices.
•Apr 28, 2019•0 citations