The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.

Tunnel Junction Thermometry and Thermalisation of Electrons

Tommy Holmqvist

Doctoral dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Information and Natural Sciences for public examination and debate in Auditorium AS1 at the Aalto University School of Science and Technology (Espoo, Finland) on the 9th of April 2010 at 12 noon.

Overview in PDF format (ISBN 978-952-60-3079-1)   [3966 KB]
Dissertation is also available in print (ISBN 978-952-60-3078-4)


In this work, normal metal and superconducting tunnel junctions have been studied. In particular applications in low temperature electronic thermometry are investigated. The double oxidation method for achieving high resistance junctions is described and shown to produce high quality devices. A new invention, the single junction thermometer (SJT), is described, and proof of the concept experiments demonstrating the functionality of the device are described. A key feature of the SJT is a well controlled electromagnetic environment surrounding a single junction. It is shown that embedding a single junction within arrays of other junctions is a superior way for controlling the environment as compared to previously proposed methods. Improved thermalisation of electrons is shown to be beneficial for the performance of superconducting RSFQ (Rapid Single Flux Quantum) devices. The so called grey zone of the most basic of these devices, the balanced comparator, is investigated. Improved performance based on metallic cooling fins has been achieved. In the same spirit improved thermalisation of the Coulomb blockade thermometers extends their operation towards lower temperatures. A method employing thick metallic islands was developed and tested to this end.

This thesis consists of an overview and of the following 5 publications:

  1. A. M. Savin, J. P. Pekola, T. Holmqvist, J. Hassel, L. Grönberg, P. Helistö, and A. Kidiyarova-Shevchenko. 2006. High-resolution superconducting single-flux quantum comparator for sub-Kelvin temperatures. Applied Physics Letters, volume 89, number 13, 133505, 3 pages.
  2. T. Holmqvist, M. Meschke, and J. P. Pekola. 2008. Double oxidation scheme for tunnel junction fabrication. Journal of Vacuum Science and Technology B, volume 26, number 1, pages 28-31.
  3. E. Isosaari, T. Holmqvist, M. Meschke, M. Heinonen, and J. P. Pekola. 2009. Thermometry by micro and nanodevices. The European Physical Journal - Special Topics, volume 172, number 1, pages 323-332.
  4. Jukka P. Pekola, Tommy Holmqvist, and Matthias Meschke. 2008. Primary tunnel junction thermometry. Physical Review Letters, volume 101, number 20, 206801, 4 pages.
  5. Tommy Holmqvist, Jukka P. Pekola, and Matthias Meschke. 2009. Influence of environment on tunneling thermometry. In: Meri Helle (editor). Proceedings of the Conference on Micro- and Nanocryogenics. Espoo, Finland. 3-5 August 2008. Springer. Journal of Low Temperature Physics, volume 154, numbers 5-6, pages 172-178.

Keywords: thermometry, Coulomb blockade thermometer, single junction thermometer, tunnel junctions

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Last update 2011-05-26