Browsing by Subject "Josephson junction"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Open Access Design and implementation of an automated low noise cryogenic characterization system for high-Tc Josephson junctions(Bilkent University, 2004) Yılmaz, AbdulvahitSince the discovery of high temperature superconductors, superconductivity became one of the fast emerging technologies being used in numerous applications where in many of these applications Josephson junctions form the basis for superconducting electronic devices and circuits. In order to use the Josephson junctions effectively and fabricate them reproducibly with the same properties, their characterization should be done where their main characterization is the current vs. voltage measurement. This study concentrates on the design and implementation of two automated low noise cryogenic characterization systems that let current vs. voltage, dynamic resistance vs. current, and resistance vs. temperature characterizations be done at temperatures ranging from 63.15K to 120K for the Josephson junctions. In this study, also the fabrication and preparation steps of different types of high-Tc Josephson junctions, such as step edge and bicrystal junctions of junction arrays, gradiometers’, and dc-SQUIDs’ for characterization, are explained. By using the established characterization systems, the current vs. voltage behaviors for different types of junctions could be measured and classified.Item Open Access Junction characteristics and magnetic field dependencies of low noise step edge junction Rf-SQUIDs for unshielded applications(IEEE, 2003-06) Fardmanesh, Mehdi; Schubert, J.; Akram, Rizwan; Bozbey, Ali; Bick, M.; Banzet, M.; Lomparski, D.; Zander, W.; Zhang, Y.; Krause, H-J.Step edge grain boundary (GB) junctions and rf-SQUIDs have been made using pulsed laser deposited Y-Ba-Cu-O films on crystalline LaAlO3 substrates. The steps were developed using various ion-beam etching processes resulting in sharp and ramp type step structures. Sharp step based GB junctions showed behavior of serial junctions with resistively shunted junction (RSJ)-like I-V characteristics. The ramped type step structures resulted in relatively high critical current, Ic, junctions and noisy SQUIDs. The sharp steps resulted in low noise rf-SQUIDs with a noise level below 140 fT/Hz12/ down to few Hz at 77 K while measured with conventional tank circuits. The Ic of the junctions and hence the operating temperature range of the SQUIDs made using sharp steps was controlled by both the step height and the junction widths. The junction properties of the SQUIDs were also characterized showing RSJ-like characteristics and magnetic field sensitivities correlated to that of the SQUIDs. Two major low and high background magnetic field sensitivities have been observed for our step edge junctions and the SQUIDs made on sharp steps. High quality step edge junctions with low magnetic field sensitivities made on clean sharp steps resulted in low 1/f noise rf-SQUIDs proper for applications in unshielded environment.Item Open Access Noise, junction characteristics, and magnetic field dependencies of bicrystal grain boundary junction Rf-SQUIDs(IEEE, 2003) Fardmanesh, Mehdi; Schubert, J.; Akram, Rizwan; Bick, M.; Banzet, M.; Zander, W.; Zhang, Y.; Krause, H-J.Bicrystal grain boundary (GB) Josephson junctions and rf-SQUID's were made of 200 nm thick PLD YBCO films on bi-crystal SrTiO3 substrates. The junction characteristics were studied to investigate optimal parameters in the rf-SQUID) layout designs and the limits imposed by the technology. The I c of 3 to 8 μm wide test junctions scaled with the junction widths, showing clear linear RSJ-like I-V characteristics at 77 K. All the junctions showed hysteretic RCSJ-like behavior at very low temperatures. Classical Josephson flux motion type (long junction) nonlinearity in I-V curves of all the junctions was also observed at lower temperatures with systematic dependence on the junction widths. Measurements of the magnetic field dependence of the Ic of the junctions resulted in junction width dependent well-defined Fraunhofer-pattern like characteristics. The obtained characteristics of the junctions led to feasible criteria for the rf-SQUID layouts with desired device characteristics. Rf-SQUID's were made using designs for optimal performance at 77 K while avoiding large superconducting weak links across the substrate GB. Devices with low noise characteristics and junction field sensitivities proper for operation in environmental background magnetic fields were obtained. A nonsystematic spread of optimal working temperature of the SQUID's were also observed which is associated to the spread of the junction parameters caused by the defects at the GB of substrates.Item Open Access Study of junction and bias parameters in readout of phase qubits(2012) Zandi H.; Safaei, S.; Khorasani, S.; Fardmanesh, M.The exact numerical solution of the nonlinear Ginzburg-Landau equation for Josephson junctions is obtained, from which the precise nontrivial current density and effective potential of the Josephson junctions are found. Based on the resulting potential well, the tunneling probabilities of the associated bound states are computed which are in complete agreement with the reported experimental data. The effects of junction and bias parameters such as thickness of the insulating barrier, cross sectional area, bias current, and magnetic field are fully investigated using a successive perturbation approach. We define and compute figures of merit for achieving optimal operation of phase qubits and measurements of the corresponding states. Particularly, it is found that Josephson junctions with thicker barriers yield better performance in measurements of phase qubits. The variations of characteristic parameters such as life time of the states due to the above considered parameters are also studied and discussed to obtain the appropriate configuration setup.