New superconductor technology developed by VTT

VTT has long been working on technology based on superconductors which operate at extremely low temperatures. The development target has been the sensors needed in magnetic imaging of the brain, precision metres and indicators of electromagnetic radiation. One of the most recent breakthroughs is the nanotransistor developed by VTT, which operates in extreme cold. The transistor is particularly suitable for the measurement of small signals.

The transistor can be used to amplify outgoing signals of extremely sensitive electromagnetic radiation indicators. Other potential applications include astronomical measurements, security cameras and even a reform of the SI system of units.

Several physical phenomena can only be exploited at very low temperatures. The innovation, known as the Bloch Oscillating Transistor (BOT) operates at temperatures as low as 0.1 Kelvin (equivalent to 0.1 degrees Celsius above absolute zero). The advantage of such extreme cold is that there is little interference with the signals to be measured as the noise resulting from motion of atoms and electrons in the substance is small.

The transistor was invented at VTT. Its modelling, fabrication and trial measurements were accomplished in collaboration with the Low Temperature Laboratory of Helsinki University of Technology. The BOT transistor is based on a nanometric Josephson junction whose properties and applications are being actively researched by physicists around the world. The transistor developed by VTT provides a unique addition to the fascinating world of such objects.

It may be possible to utilise the new transistor in metrology, i.e. the branch of science concerned with measurement, as the comparison of very small currents (range one pA) is problematic with present methods. It may also be applicable as a comparison amplifier in the so-called quantum metrological experiment. Performing such a test would make it possible to define the SI system of units with natural constants, that is, with the speed of light, electronic charge and Planck's constant, which have the same value always and everywhere.

Antti Manninen, Group Leader at the Centre for Metrology and Accreditation (MIKES) is pictured beside the Josephson quantum voltage standard cooled by liquid helium. High resolution image (913 Kb) Photo: Jaani Nissilä

The development work on the BOT transistor and the quantum voltage standard form part of the doctoral dissertation of VTT researcher Juha Hassel, which will be publicly defended at the Helsinki University of Technology on 9 November 2004. The supervisors of the dissertation are Professor Heikki Seppä of VTT and Professor Pertti Hakonen of TKK.

More information: www.vtt.fi/inf/pdf/publications/2004/P551.pdf

VTT Information Technology Juha Hassel, Research Tel. +358 9 456 6771, +358 50 367 3482 juha.hassel@vtt.fi	Centre for Metrology and Accreditation Scientist Antti Manninen, Group Leader Tel. +358 9 456 6272, +358 40 514 8658 antti.manninen@mikes.fi