Hochfrequenzverhalten gekoppelter und ungekoppelter Josephson-Kontakte auf der Basis von Hochtemperatur-Supraleitern
Hochfrequenzverhalten gekoppelter und ungekoppelter Josephson-Kontakte auf der Basis von Hochtemperatur-Supraleitern
Josephson junctions made from high temperature superconductors (HTS) are active highfrequency devices which can be used as oscillators or frequency mixers in the submillimeter wave region. The frequencies of these electromagnetic waves range from 300 GHz up to 3 THz. Up to now...
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Personal Name(s): | Scherbel, Jens (Corresponding author) |
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Contributing Institute: |
Publikationen vor 2000; PRE-2000; Retrocat |
Imprint: |
Jülich
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag
2001
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Physical Description: |
V, 92 p. |
Document Type: |
Report Book |
Research Program: |
ohne Topic |
Series Title: |
Berichte des Forschungszentrums Jülich
3880 |
Link: |
OpenAccess OpenAccess |
Publikationsportal JuSER |
Josephson junctions made from high temperature superconductors (HTS) are active highfrequency devices which can be used as oscillators or frequency mixers in the submillimeter wave region. The frequencies of these electromagnetic waves range from 300 GHz up to 3 THz. Up to now, this wave band is a relatively unexploited region of the electromagnetic spectrum because it is very difficult to produce and detect submillimeter-waves. However, submillimeter-wave technologies are becoming important in many practical scientific applications such as radio astronomy, atmospheric research, plasma diagnostics and THz imaging, recently.In this work, the behaviour HTS Josephson junctions have been investigated experimentallyand theoretically with the aim to THz-applications. In the first part the behaviour of intrinsic Josephson junction stacks are measured, and the possibility of phase locking is discussed by the theoretical analysis of two different shunt technologies depending on the parameter spread of the junction and the shunt parameters. It could be shown that stacks made from sputtered BSCCO layers does not act as intrinsic Josephson junction arrays because of their many micro shorts resulting from the layer growth. However, the stacks made from sputtered TBCCO show clear intrinsic Josephson junction behaviour. But their quasiparticle branches in the current-voltage characteristic deviate from the behaviour predicted by the common used RCSJ model. These branches can be discussed within a tunneling model using d-wave superconductor density of states. A temperature dependent current distribution and a zero bias anomaly was found. Furthermore, the coherent behaviour is studied for intrinsic arrays with additional side-wall shunts. The existence of thresholds of phase locking at especial junction and shunt parameters are demonstrated and discussed in regard to THz-oscillator applications. It was found that the Josephson junctions in a stack can be phase locked even if they have a parameter spread in the critical current up to 15% using a resonant shunt.In the second part of this work the mixing properties of HTS bicrystal Josephson junctions as wave guide mixers for 115 and 345 GHz have been investigated. A variable backshart and E-plane tuner in the mixer block allowed to control the impedance matching between the junction and the rf-environment. The intermediate frequency were 1.4 GHz. The double-side band (DSB) mixer noise temperature and the conversion efficiency were determined using the hot/cold method. It was observed that the noise temperature was strongly dependent on the matching conditions. The lowest noise temperatures have been obtained for tuner positions supporting the formation of a subharmonic step which appeared between the zeroth and first Shapiro step. The physical background of the appearance of this feature and their influence to the noise temperature is discussed. At an operating temperature of T=20 K a lowest DSB mixer noise temperature of 1003 K and a mixer conversion efficiency of -0.8 dB was obtained. It could be shown that the conversion efficiency depends not only from the dynamic resistance in the operating point itself but also from the dynamical resistance of its neighbourhood. The thermal noise dependence of the noise temperature was investigated in detail and is explained by the physical background. Different saturation effects have been found by measuring the relative heterodyne response. The reasons and possibilities to suppress these saturation effects are discussed. |