PRO VOLT: Programmable voltage standard for AC and DC metrology

• Unité de recherche: PCRD EU
• Numéro de projet: 98.0161
• Titre du projet anglais: PRO VOLT: Programmable voltage standard for AC and DC metrology

Mots-clé (Anglais)

voltage standards; quantum metrology; Josephson effect; electricity

Autre Numéro de projet (Anglais)

EU project number: SMT4-CT98-2239

Programme de recherche (Anglais)

EU-programme: 4. Frame Research Programme - 2.2 Measurements and testing

Description succincte (Anglais)

See abstract

Autres indications (Anglais)

Full name of research-institution/enterprise:
Bundesamt für Metrologie und Akkreditierung METAS

Partenaires et organisations internationales (Anglais)

PTB Physikalisch-Technische Bundesanstalt (D); IEN Istituto Elettrotecnico Nazionale (I); VTT Technical Research Center of Finland (FIN); JV Norwegian Metrology and Accreditation Service Justervesenet (NO); SINTEF Electronics and Cybernetics (NO); NPL National Physical Laboratory, Teddington (UK); LCIE Laboratoire Central des Industries Electriques (F); SP Swedish National Testing and Research Institute (S); NMi Nederlands Meetinstituut (NL); PREMA Prema Präzisionelektronik GmbH, (D)

Résumé des résultats (Abstract) (Anglais)

Nowadays, superconductor-insulator-superconductor (SIS) Josephson junction arrays are routinely used to realize the SI unit of voltage, the volt. The intrinsic physical properties of this type of junctions make them sensitive to external noise and prone to chaotic behavior. With the advancement of the technology, several new types of Josephson junction arrays have been developed recently. Theses arrays are based on superconductor - normal metal - superconductors (SNS) and SINIS junctions. The new types of junctions are intrinsically more stable and allow a faster voltage selection. Therefore, this technological progress will broaden the application of the Josephson effect in metrology. In particular, programmable voltage standard and D/A converters of fundamental accuracy can be envisioned. Nine European national laboratories and an electronic company are co-operating in the ProVolt project.
At METAS, the first task was to design and fabricate a new cryoprobe for the measurements of SINIS arrays. This cryoprobe allows to measure binary arrays at a frequency of 75 GHz. An oversized circular wave guide brings the microwave to the array. The wiring allows to feed up to 13 segments on the array. In addition, two precision wires used for voltage measurement are provided. The whole probe is inserted in a transportable helium Dewar at a temperature of 4 K.
In 2000, the measurements with a SINIS array provided by the PTB were started. A thorough characterization of the physical properties of the array was performed. The array was found to perform very well. Clear voltage steps were observed. It was found that the voltage steps of the various segments of the binary array had different widths depending on their location in the array. This effect was clearly not caused by a spread in the junction's parameters during the fabrication process. Instead, it was due to an inhomogeneous distribution of the power to the array. Due to the large number of junctions, this is a difficult and complex problem that might be solved in the next generation of arrays.
In addition, a precise test of the plateau flatness was performed by making a comparison between the SINIS array and our SIS voltage standard. It was found that the SINIS voltage step was not perfectly flat when observed at the nanovolt level. That is not what was observed earlier when the array was measured at PTB. Aging of the array or its high sensitivity to external noise might be the cause of that slight deviation. This point will be further investigated in a close future.
In conclusion, the ProVolt project was very successful for METAS. A new measurement system was developed that allows to test SINIS Josephson junction arrays. Precision measurements were carried out to asses the accuracy of the new SINIS arrays. A collaboration has been initiated between METAS and PTB. This collaboration will certainly continue because more measurements are needed before the new arrays can reliably be used as primary voltage standards.

Références bases de données (Anglais)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 98.0161