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Ultrasensitive Cold-Electron Bolometer

Ian Agulo (Institutionen för mikroteknologi och nanovetenskap, Kvantkomponentfysik)
Göteborg : Chalmers University of Technology, 2007. ISBN: 978-91-7291-945-7.- 109 s.

The Cold-Electron Bolometer (CEB) is an ultrasensitive device designed for the detection of cosmic microwave background radiation. The key to its sensitivity is the electron cooling of the absorber by the superconductor-insulator-normal metal (SIN) tunnel junction. At a voltage near and below the superconducting gap, the electrons in the absorber are cooled well below the phonon temperature of the normal metal. This translates to the enhanced sensitivity of the CEB. This thesis describes the work we have done on the optimization of electron cooling of the normal metal absorber, and our measurement of the sensitivity of the CEB. We have optimized the electron cooling of the absorber by SIN tunnel junctions. The best electron cooling was achieved when normal metal traps were added in proximity to the superconducting electrodes in addition to the advanced geometry of the superconducting electrodes. With these modifications, we have decreased the electron temperature by 198 mK. With just the advanced geometry, the electron temperature drop was 129 mK. With just a simple geometry, the drop in temperature was 56 mK. The noise equivalent power (NEP) of the CEB was also measured at 100 mK to be at the level of 10^-18 W/Hz^1/2 at 1 kHz. The NEP was obtained by measuring the noise of the CEB, and then dividing that by its power responsivity, dV/dP. The main limitation in our measurements was the noise component from the amplifier. Finally, we have made measurements on the temperature sensitivity of the SIN tunnel junctions. We have compared the sensitivity between single and ten SIN junctions in series and found that it increases proportionally to the number of junctions. The best temperature responsivity obtained for 10 junctions was approximately 15 μV/mK. Using such thermometer, we have been able to measure the temperature stability of the Oxford Instruments cryogenfree refrigerator to be plus/minus 250 μK for a period of 8 hours. The resolution of the thermometer was measured to be plus/minus100 μK, limited by the noise due to the amplifier. The current and future works are also discussed. These include: a CEB array designed to distribute the total power load, improving further the sensitivity; a one-thousand SIN tunnel junction series thermometer in order to realize and understand the fundamental limitation of such a device; a superconducting cold-electron bolometer (SCEB) for high background power loads; and different read-out systems including an on-chip quasiparticle amplifier (QPA).

Nyckelord: cold-electron bolometer (CEB), superconducting cold-electron bolometer (SCEB), electron cooling, SIN tunnel junctions, noise equivalent power, responsivity

Denna post skapades 2007-05-24. Senast ändrad 2013-09-25.
CPL Pubid: 42053


Institutioner (Chalmers)

Institutionen för mikroteknologi och nanovetenskap, Kvantkomponentfysik


Mesoskopisk fysik

Chalmers infrastruktur

Relaterade publikationer

Inkluderade delarbeten:

Optimization of the electron cooling by SIN tunnel junctions

Terahertz spectroscopy by Josephson oscillator and cold-electron bolometer

Effective Electron Microrefrigeration by SIN Tunnel Junctions with Advanced Geometry of Electrodes and Normal Metal Traps


Datum: 2007-06-08
Tid: 13:15
Lokal: Kollektorn, MC2, Kemivägen 9, Chalmers University of Technology
Opponent: Jesper Mygind, Professor (Docent), Department of Physics, Technical University of Denmark (DTU), Denmark

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Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie 2626

Technical report MC2 - Department of Microtechnology and Nanoscience, Chalmers University of Technology 101