| 1. |
- Bevilacqua, Stella, 1981, et al.
(författare)
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Fast room temperature THz bolometers
- 2013
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Ingår i: International Conference on Infrared, Millimeter, and Terahertz Waves, IRMMW-THz. - 2162-2027 .- 2162-2035. - 9781467347174 ; , s. 1-2
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Konferensbidrag (refereegranskat)abstract
- A responsivity of >100 V/W was measured at roomtemperature for nano scale bolometers integrated with planar spiral antennas covering a frequency range from 100 GHz to 3 THz. Currently a NEP of about 200 pW/Hz^0.5 was experimentally obtained.
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| 2. |
- Bevilacqua, Stella, 1981, et al.
(författare)
-
Study of IF bandwidth of MgB2 phonon-cooled hot-electron bolometer mixers
- 2013
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Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 3:4, s. 409-415
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Tidskriftsartikel (refereegranskat)abstract
- A noise bandwidth (NBW) of 6-7 GHz was obtained for Hot-Electron Bolometer (HEB) mixers made of 10 nm MgB2 films. A systematic investigation of the (IF) gain bandwidth as a function of the MgB2 film thickness (30 nm, 15 nm and 10 nm) is also presented. The gain bandwidth (GBW) of 3.4 GHz was measured for a 10 nm film, corresponding to a mixer time constant of 47 ps. For 10 nm films a reduction of the GBW was observed with the reduction of the critical temperature (Tc). Experimental data were analyzed using the two-temperature model. From the theoretical analysis, the electron-phonon time (τe-ph), the phonon escape time (τesc) and the electron and phonon specific heats (ce, cph) were extrapolated giving the first model for HEB mixers of MgB2 films.
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| 3. |
- Bevilacqua, Stella, 1981, et al.
(författare)
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Submicrometer MgB2 hot electron bolometer mixers
- 2013
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Ingår i: The 24th International Symposium on Space Terahertz Technology.
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Konferensbidrag (refereegranskat)abstract
- Phonon-cooled hot electron bolometer mixers based on MgB2 film are promising candidates for THz radio astronomy at frequency above 1 THz. The short electron-phonon interaction time and the high critical temperature of the MgB2 (39 K in the bulk), compared to other intermetallic compounds, make it suitable for applications where wide IF bandwidth and low noise are needed. The currently achieved gain and noise bandwidths are 3.4 GHz and 7 GHz for HEBs fabricated in 10 nm MgB2 films. The noise temperature of 800 K was measured at 600 GHz local oscillator (LO) frequency using the Y-factor technique.MgB2 has been demonstrated to be sensitive to the oxygen as well as water, therefore it makes the fabrication of sub-µm HEBs very challenging. HEBs were fabricated using electron beam lithography in 10 nm MgB2 films with a bolometer area in the range of 0.09 and 0.25 µm2. We report the performance of the devices respect to the noise temperature at LO frequency up to 2.5 THz. Using the isothermal technique the LO power requirement was estimated respect to the bolometer area. Based on the material parameters obtained from the experiments, the two temperature model simulations showed a gain bandwidth as large as 8-10 GHz for thin MgB2 films.
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| 4. |
- Bevilacqua, Stella, 1981
(författare)
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Superconducting THz mixers based on MgB2 film
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Superconducting NbN hot electron bolometer (HEB) mixers are widely used in terahertz radio astronomy. Such mixers have superior performance compared to SIS and Schottky diode mixers at frequency above 1THz. However, their drawback is a limited IF bandwidth. Therefore, as radio astronomy advances towards higher frequencies, mixers with even wider gain bandwidth are required. The gain bandwidth of the HEB mixers is determined by two consequent processes in the electron energy relaxation: the electron phonon interaction and the phonon escape into the substrate with corresponding time constants for each process. The electron-phonon interaction time is inversely dependent of the electron temperature of the film which is close to the critical temperature of the superconductor. The escape time is dependent of the film thickness. Materials with higher critical temperature and shorter electron relaxation time are needed to improve the IF bandwidth. The discovery of the superconductivity in the intermetallic compound magnesium diboride (MgB2) has generated a great interest in this research field. The high critical temperature and the short electron phonon interaction time make the MgB2 very attractive for HEB mixers fabrication aiming for better HEB mixers performances. In this thesis, novel terahertz HEB mixers based on magnesium diboride thin films are presented. MgB2 HEBs integrated with spiral antenna were fabricated, characterized and studied. The gain bandwidth was investigated with respect to the thickness and the critical temperature of the film. A gain bandwidth of 1.3GHz, 2.3GHz and 3.4GHz corresponding to a mixer time constant of 130 ps, 70 ps and 47 ps was measured in 30 nm, 15 nm and 10 nm MgB2 films, respectively. Another important figure of merit for receivers is the noise temperature which is influenced by several factors such as the dimension of the HEB and the critical current. For HEB mixers made from 10 nm MgB2 film the lowest mixer noise temperature was 600K measured at 2K bath temperature and 600GHz local oscillator (LO) frequency. Finally, using the two temperature model the experimental data were analyzed and the electron phonon interaction time, τe-ph of 7 to 15 ps, the phonon escape time, τesc of 6 to 42 ps and the specific heat ratio, ce/cph of 1.35 to 9 ps were extracting giving the first model for HEB mixers made of MgB2 films. Based on this research a gain bandwidth as large as 8-10GHz has been predicted in very thin MgB2 films.
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