Master Degree / Yüksek Lisans Tezleri
Permanent URI for this collectionhttps://hdl.handle.net/11147/3008
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Master Thesis Terahertz Wave Sensitive Superconducting Bolometric Detector(Izmir Institute of Technology, 2015) Semerci, Tuğçe; Özyüzer, Lütfi; Özdemir Köklü, MehtapTerahertz (THz) waves has varied properties than other part of the electromagnetic spectrum which between microwave and infrared and has 0.3-10 THz frequency range and 3-0.03 mm wavelength. There are many areas to utilize from THz radiation that defense industry particularly security part such as detecting of unknown materials, poison or explosive matters. Additionally, THz waves can pass through leather, fabric and paper despite of metal and water and there is no enough energy to ionize the atoms in THz radiation. That’s why, THz radiation is not hazardous for human. Many detectors are developed to use these benefit of THz radiation. Bolometric detector is preferred between these detectors to detect the radiation above 1 THz frequency. Bi2Sr2CaCu2O8+δ (Bi2212) single crystal was used in literature for the first time to detect the THz waves with superconducting bolometers with our study. In this study, epoxy was used to transfer Bi2212 single crystal onto the sapphire substrate. Intended thickness was acquired by scotch tape via cleaved crystal mechanically. Edge of crystals were cut pyramid shape to provide each layer to contact with gold, crystal and silver epoxy. 150-200 nm crystals were shadowed by aluminum foil to deposit roughly 200 nm gold. Then clean room process was implemented to prepare our samples to electron beam lithography. Log-periodic antenna and four point contact structure was placed onto the crystals then UV light, developer and ion beam etching system were performed. Cryostat was designed and produced to measure electrical and bolometric measurements. Resistance-temperature in a-b axis gave the around 90 K as critical temperature. Bolometric measurement was done via superconducting transition region to decide the selected temperature to measure the change of resistance by sending signal from Stefan-Boltzmann Lamp in specific seconds. Change of resistance was observed from resistance-time measurement for bolometric measurement. Response time was calculated approaching 825 ms from the result of bolometric measurement. Our measurement set-up has limitation to read right data. Lock-in-amplifier may use to more accurate result.Master Thesis Pixel Array Application of High Temperature Superconducting Ybco Transition Edge Infrared Bolometers(Izmir Institute of Technology, 2009) Pekerten, Barış; Abukay, DoğanIn 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.Master Thesis High Temperature Superconducting Yba2cu3o7-Δ Thin Flims and Bolometers(Izmir Institute of Technology, 2006) Öktem, Bülent; Abukay, DoğanIn 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.