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Design and Fabrication of a High Detectivity HTS Bolometer and Investigation of Geometrical Effects on its Responsivity and Detectivity

Moftakharzadeh, Ali | 2012

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 42724 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Fardmanesh, Mehdi
  7. Abstract:
  8. Detectors play an important role in almost all scientific experiments and the results of the experiment highly depend on the performance of the applied detector (e.g. the detector detectivity, noise, detection threshold, time constant, …). In general a detector is defined as a device which transforms a quantity (e.g. pressure, energy, photon, …) to another one(e.g. mechanical displacement, electrical current, voltage, …). High temperature superconductor transition edge bolometers (TEB) are one of the most promising devices that due to the wavelength independent nature of their optical response can be used to detect the electromagnetic radiation over the whole spectrum from x-ray to the far inferared,. The principle operation of these detectors is based on the steep drop in the resistance of the bolometer near the superconductive transition temperature. They cover a wide range of applications such as space radiometry and spectrometry, optical communication, thermal sensing and imaging for biomedical and military purposes, Security THz camera, and single photon detection. The main focus of this thesis is on investigation and optimization of the detectivity of HTS bolometers and design and fabrication of a high detectivity bolometer. The effect of geometrical parameters such as substrate thickness, device area, surface absorption, substrate material, and thermal conductance on the responsivity and detectivity of HTS bolometers are thoroughly investigated both theoretically and experimentally. Using an analytical approach the maximum achievable detectivity for a specified structure is calculated. In order to verify the theoretical results several bolometric detectors have been fabricated and characterized. A new absorber layer consisting of Cu-C nano-composites is applied for the first time to increase the optical response of this type of detectors. Considering the achieved theoretical and experimental results, a new configuration for fabrication of a high detectivity bolometer is suggested. This configuration is based on hybrid semiconductor-superconductor technology. Finally, a bolometer using this new configuration has been fabricated and characterized. The results of optical response and noise measurement of this device is presented. We have used a carbon-black absorber layer to increase device response. The detectivity calculation for this device shows a high value of 2?1010 cm?Hz/W
  9. Keywords:
  10. High Temperature Superconductor ; Superconductive Edge Transition Bolometer ; Detectivity ; Noise ; YBCO Superconductor ; Optical Responsivity

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