Browsing by Subject "Superconductor"

Now showing 1 - 6 of 6

Open Access
Design and implementation of A 06 GHz - 09 GHz RF-SQUID Read-out system and investigation of rf-SQUID signal characteristics
(2005) Eker, Taylan
Design and implementation of a transceiver system for rf-SQUID (Superconducting Quantum Interference Device) operation is investigated in this work. Besides, experiments to characterize the rf-SQUID have been performed using the implemented system. The steps in system design and implementation are presented. The difficulties and drawbacks of the system are reported and alternative techniques required to overcome these problems are determined. Also, for the operation of the rf-SQUID at much higher frequencies, different transceiver architecture is proposed and possible drawbacks are stated. Using implemented system, several experiments were performed on two high Tc rfSQUID gradiometers with a tank-circuit resonating at 720 MHz. In these experiments, the frequency and amplitude of the applied rf signal were swept and output flux to voltage transfer signal (modulation added by rf-SQUID), Vspp, and incoming rf signal spectrum are reported and analyzed.
Open Access
Design and implementation of an automated low noise cryogenic characterization system for high-Tc Josephson junctions
(2004) Yılmaz, Abdulvahit
Since 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.
Open Access
Fabrication and optimization of rf-SQUID and SQUID integration assembly for high resolution magnetic imaging systems
(2005) Akram, Rizwan
Superconducting QUantum Interference Devices or SQUIDs are by far the most sensitive devices known for sensing magnetic flux down to a resolution of about 10−21Wb and finds innumerous applications in various fields. In order to apply these sensors to sense nano structures or to use in antibody or antigen ammunoassay experiments, especially in unshielded environments at Liquid Nitrogen temperatures, one needs to optimize the SQUIDs for high SNR and low background magnetic field sensitivity. The chief motivation for this research work and this thesis is to optimize and characterize HTc rf-SQUIDs so that high field sensitivity and high spatial resolution could be obtained. During the course of this study, rf-SQUIDs were fabricated using SEJ and Bicrystal technology and optimized for the above mentioned characteristics. In the next stage, these optimized sensors were integrated into an imaging system after a thorough investigation on problems related to the front-end assembly of such a system. Different SQUID microscope systems have been designed, fabricated, and tested in order to achieve high field sensitivity and high spatial resolution magnetic imaging under the constraint of keeping the sample at room temperature, while the SQUID is in Liquid Nitrogen Temperature. Using the developed systems, magnetic imaging of room temperature samples with sensitivities in the range of about 100fT/√ (Hz) and spatial resolution of about 100 µm were achieved
Open Access
HTSC superconducting edge-transition infrared detectors; principles, fabrication, and characterization
(2000) Akram, Rizwan
Since the discovery of High temperature superconductors, superconductivity became one of the fast emerging technologies being used in numerous applications ranging from large-scale to small-scale applications such as IR,-detectors. High temperature superconductors such as YBü'zCuíOj due to their properties are the prime candidates for the fabrication of detectors. Their responsivity and detectivity can be improved by changing the design and SC characteristics. In this thesis, one-dimensional thermal model has been considered to improve the characteristic parameters of the SC. Based on the model, the annealing profile and manufacturing process is modified to further enhance the responsivity and detectivity of the detectors. A characterization setup is established to perform dc & ac measurements at low temperatures. In order to improve the cryogenic setu]), a thermal equivalent model for the system is also proposed.
Open Access
İnvestigation, modeling, and applications feasibility of the thermal crosstalk in high Tc transition edge bolometer arrays
(2006) Bozbey, Ali
So far, the high Tc transition edge bolometer (TEB) devices are mostly used as single pixel detectors. Recently, there are a number of groups working on the 2-4 pixel array applications of the high Tc TEB. Though the target spectrum of the TEB is far IR and mm-waves, we are using a near IR laser source in our investigation due to practical reasons since the response analysis is similar. We have designed and implemented 4-pixel Y Ba2Cu3O7−δ (YBCO) edge transition bolometer arrays. The crosstalk study was made possible through the illumination of the sense-devices and measuring the voltage response of the blocked read-out device in the same array. This was done using a silver coated shadow mask. In order to prevent thermal artifacts created by the mask, the mask was made in free standing configuration on top of the devices. The devices were made of 200 nm and 400 nm thick pulsed laser deposited YBCO films on SrT iO3 and LaAl2O3 substrate materials. In this thesis, we made the qualitative investigation of the dependence of the thermal crosstalk on the various device parameters such as the substrate material, device layout, YBCO film thickness, operating temperature, and modulation frequency. Then, based on the experimental results, we proposed an analytical thermal model. We proposed two models: i) Basic model, which takes into account only the lateral heat diffusion in the substrate for quick design purposes ii)Analytical model, which takes into account the lateral heat diffusion, vertical heat diffusion, and the effect of the leaking laser radiation through the shadow mask, for detailed design purposes and verifying the qualitative analysis. Finally, we proposed and verified possible applications of the thermal crosstalk in TEB arrays. One proposed application of the crosstalk is the electrical free read-out of the sense pixels by utilization of the unique dependence of the magnitude and phase of the response on the thermal crosstalk between bolometer pixels in an array. The qualitative investigation made in this study is the most detailed investigation about the bolometer arrays and the proposed analytical model is the strongest among the reported ones so far in terms of fitting the experimental results, explaining the effects of the various parameters, and designing TEB arrays. The proposed crosstalk based read-out method is expected to decrease the read-out circuitry for possible TEB based applications. Since multilayer process is difficult to make in high Tc superconductors, decreasing the complexity of the read-out circuitry by half is even important and it is the first time that such a method is utilized including bolometer arrays made of different types of materials.
Open Access
Point normal metal-superconductor (NS) contact in nonballistic regime
(World Scientific Publishing, 2003) Askerzade, İ. N.; Kulik, Igor Orestovich
We analyze the point NS contact conductivity taking into account the depression of superconductivity at high-injection current density and Andreev reflection at the adaptive NS boundary. The dependence of the excess current on the voltage, as well as conductivity of contact at arbitrary voltage is obtained.