1 March 2002
PhD thesis defence Elena Bartolomé, faculty of Applied Physics, ‘Cryogenic Current Comparators with optimum SQUID readout for current and resistance quantum metrology’
The continuous miniaturization in the semiconductor industry requires the extremely accurate measurement of very small currents. These measurements rely on the existence of a very precise current standard, and calibration techniques. Until now the current was derived from the classical resistance and voltage standards. The recent discovery of the so-called SET (Single Electron Tunneling) devices, able to control electrons one-by-one, opened the possibility to develop an independent, quantized current quantum standard. The current delivered by SETs is at present very small (1-10 pA).
In order to make a standard useful for metrology, this current should be accurately scaled to larger values. This can be best done with the help of a large gain, ultra-sensitive Cryogenic Current Comparator (CCC). In a CCC two currents can be compared very accurately. The detection of the ampere-turn unbalance in the CCC is done with the help of a SQUID (Superconducting Quantum Interference Device), nowadays the most sensitive magnetic flux sensor existing. In an international cooperation between the Universities of Twente, Zaragoza (Spain) and the NMi Metrology Institute (Delft), there has been developed a large gain (1:30000) CCC with optimum SQUID readout for SET current amplification. It has been estimated that with this system, a 1-10 pA SET current could be measured with a relative uncertainty of ~10-5-10-6. The establishment of the quantum current standard would also open the door for closing the Quantum Metrological Triangle of electrical units. This experiment, consisting in realizing Ohm's well-known law (I=VR) with the current, voltage and resistance quantum standards, would allow verifying the coherence of the fundamental constants of nature involved with a great accuracy.
Supervisor: prof. dr. Horst Rogalla
second supervisor: dr. ir. Jaap Flokstra
(Zaragoza: dr. Conrado Rillo)
information: drs. B. Meijering, telefoon (053) 489 43 85