Izmir Institute of Technology

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Fabrication and characterizarion of superconductor YBCO Josephson junctions
(Izmir Institute of Technology, 2008) Algül, Berrin Pınar; Abukay, Doğan
A well-controlled, high-yield Josephson junction production process forms the basis of superconducting electronic device and circuit technology. In order to use the Josephson junctions effectively and fabricate them reproducibly, their structural and electrical characterization should be performed.This study concentrates on the fabrication and characterization of high temperature bicrystal grain boundary Josephson junctions fabricated onto 24-dand 30-degree SrTiO3 bicrystal substrates using high quality YBa2Cu3O7-. (YBCO) thin-films.200 nm thick YBCO thin films were deposited using a dc Inverted Cylindrical Magnetron Sputtering technique by investigating the thin film deposition conditions in order to obtain device quality films. The superconducting properties of the thin films were determined by electrical characterizations, consisting of resistance versus temperature and magnetic susceptibility versus temperature measurements. Structural properties were analyzed by Atomic Force Microscope, Scanning Electron Microscope and X-Ray Diffraction.Prepared thin film samples were patterned as bicrystal grain boundary Josephson junctions by standard photolithography and chemical etching processes. The current-voltage characteristics of the Josephson junctions were performed at 77 K under zero and non-zero applied field in magnetically shielded environment. The critical current values (Ic), normal resistance (Rn) and IcRn product of the output signals were determined, and the values were discussed as function of the film growth conditions. The optimization of the Josephson junctions was performed in order to improve both the signal performance and the stability of our devices against thermal cycling.
Fabrication of Lu doped YBCO thin films by pulsed laser deposition technique and their characterization
(Izmir Institute of Technology, 2010) Sezer, Bahtiyar Şirvan; Abukay, Doğan
Nearly twenty years ago YBCO was the first superconductor discovered with a transition temperature above the boiling point of liquid nitrogen, the .fascinating. limit for high temperature superconductivity. From the day forward, the interest in this ceramic compound has not diminished. YBCO is one of the most promising materials for the application of high temperature superconductors (HTS) because it is able to carry a technically useful current density in applied fields at 77 K. A lot of experiments guided to investigate the basic properties of the HTS and to further the theoretica understanding of them also used YBCO, because this progress has been achieved in the preparation of bulk samples, and especially thin films deposited by a various methods. The aim of the experimental investigation presented in this thesis was to produce high quality epitaxial Lutetium doped YBCO thin films on MgO substrates prepared by pulsed laser deposition. For this purpose, bulk Lu2O3 powder was mixed into YBCO by using solid-state reaction method and pressed to make a stoichiometric target for PLD process. KrF excimer laser was worked at 14 Kv with repetition rates ranging from 3 to 5 Hz to deposited Y0.9Lu0.1Ba2Cu3O7-. thin films at a substrate temperature of 800 oC. The surface of the films were characterized by employing XRD, SEM, EDX and AFM techniques.
Fabrication of YBCO thin flims by pulsed laser deposiyion technique and their charcterization
(Izmir Institute of Technology, 2010) Tozan, Şerife; Abukay, Doğan
This thesis focuses on pulsed laser deposition (PLD) system, fabrication of high temperature superconducting YBCO thin films and their characterization. In this study, the electrical and structural studies performed on laser deposited YBCO films have shown that films produced by PLD. The thin films were characterized in detail by employing structural XRD, SEM, EDX and AFM and electrical ( R-T) measurements. During this work, pulsed laser deposition system used to grow superconducting thin film on MgO single crystal substrate. Firstly PLD system was carried out by using different growth parameters. Deposited films was cooled down in situ under an oxygen atmosphere at a given pressure. The deposition tecnique has emerged as a very powerful method to make composition and microstructure controlled superconducting YBCO films.Thanks to rapid heating and evaporation of the target and interaction of the laser beam with evaporated materials leading to formation of a high temperature plasma PLD system is different from other thin film growth system.However, major problem was particulates emmission which was shown SEM,we solved this problem by chaning distance between target and substrate, and laser power. Furthermore Electron Dispersive X-Ray Spectroscopy (EDX) method was used to identify the chemical contents of the films.The relation between critical temperature and oxygen deficieny was investigated by means of electrical resistance R(T) and x-ray diffraction measurements.Finally, our results were compared to literature and explanied similarites.
High temperature superconducting YBa2Cu3O7-x transitation edge bolometers (TEBs) for infrared region
(Izmir Institute of Technology, 2008) Günel, Hacı Yusuf; Abukay, Doğan
The thesis focuses on electrical and bolometric characterization of high temperature superconducting YBCO transition edge bolometers. In this study, superconducting YBCO thin films grown on MgO, LaAlO3 and SrTiO3 substrates were first characterized structurally via x-ray diffraction and scanning electron microscopy.They then were patterned into bolometers and their electrical and bolometric characterizations were carried out. The results of these characterizations were fitted to the RC model. In addition, figures of merit for these devices, such as noise equivalent power (NEP) and detectivity, were measured and calculated.During this work, the patterning process was carried out by standard photolithographic processes and chemical etching. We have also investigated the effect of dimensions of our devices on the performance of bolometers. The electrical and bolometric characterizations comprised of resistance versus temperature (R-T), amplitude of response versus temperature, amplitude of response versus chopping frequency (A-F) and noise voltage measurements. Finally, the performance of our devices were compared to literature and found to be similar to or better than those of similar devices in literature.
High temperature superconducting YBa2Cu3O7-δ thin flims and bolometers
(Izmir Institute of Technology, 2006) Öktem, Bülent; Abukay, Doğan
In this work, we report the results on the response characteristics of high temperature superconducting bolometers under the infrared and optical radiation. The bolometers were made of YBa2Cu3O7-. (YBCO) thin films deposited on <100>-oriented and 10x10x1-0.5 mm3 sized single crystal MgO substrates by using DC inverted cylindrical magnetron sputtering (ICMS) technique with 200 nm thickness. The thin films were characterized in detail by employing structural (XRD, SEM, EDX, and AFM), magnetic (.-T) and electrical (R-T) measurements. We have investigated effects of temperature and modulation frequency on the magnitude and phase of the infrared response of the both large and small area bolometers. Dependence of the phase and magnitude of the response of MgO substrate YBCO edge transition bolometers to a near infrared radiation on the superconducting transition width has also been investigated in this work. We have observed that the superconductivity transition width has major effects on the response of the bolometers such as; on a dip of the phase of the response versus modulation frequency curve around 1 Hz, the rate of decrease of the magnitude of the response, and dependence of the phase of the response on temperature at mid-range modulation frequencies. Wavelength dependence of the photoresponse of YBCO edge transition bolometers has been studied. It was observed that the optical response of the devices was almost independent of the wavelength of incident light from 0.4 .m to 0.73 .m. Here we present the analysis and the possible mechanisms that can affect the response of the bolometers in the superconducting transition region.
Pixel array application of high temperature superconducting YBCO transition edge infrared bolometers
(Izmir Institute of Technology, 2009) Pekerten, Barış; Abukay, Doğan
In this thesis, we patterned pregrown epitaxial YBCO thin films on MgO, LAO and STO substrates into meander shaped high-Tc superconducting transition edge monolithic bolometers. We set up and automatized the electrical characterization processes of the bolometers. We also measured the bolometric response of the meanders to red and nearinfrared light and fit them to theoretical models in literature. We compared the single pixel bolometric responses to literature and found that our results are similar to or better than the results for similar devices in the literature.We also patterned staring arrays (focal plane arrays) and explored the resolution limit put in place by thermal crosstalk. We compared the measured crosstalk to theory and found a very good agreement. We quantified the crosstalk for our pixels. We then explored substrate etching method to decrease crosstalk via thermal isolation.

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Browsing Izmir Institute of Technology by Author "Abukay, Doğan"