Modular system for the calibration of capacitance standards based on the quantum Hall effect

• Forschungsstelle: METAS
• Projektnummer: 211.98.02
• Projekttitel Englisch: Modular system for the calibration of capacitance standards based on the quantum Hall effect

Schlüsselwörter (Englisch)

AC quantum Hall effect, unit of capacitance; coaxial ac bridge technique

Kurzbeschreibung (Englisch)

The aim of the project is the development of an AC quantum standard based on the quantized Hall resistance which can be used as a primary standard for the calibration of capacitors. The final system is planned to be able to calibrate capacitance standards with a relative uncertainty of E-7. This will enable top industrial calibration services to reduce their uncertainties by a factor of about 100.
To develop the new standard, it is aimed to use the quantized Hall resistance as the primary standard for impedance and to compare a capacitance standard to it using a quadrature bridge. The work can be divided in two main parts: 1.) Development and characterisation of QHE samples. The samples should be suitable as standards for DC resistance and have a small an well understood AC-DC difference. 2.) Development of the measurement bridge and the transfer standards.
METAS is engaged in:
-Development of a coaxial sample carrier which is compatible with the coaxial design of the AC bridges;
-Construction of temperature stabilised four-terminal pair transfer resistors;
-DC and AC characterization of QHE devices.

Projektziele (Englisch)

The aim of the project is the development of an AC quantum standard based on the quantized Hall resistance which can be used as a primary standard for the calibration of capacitors. The final system is planned to be able to calibrate capacitance standards with a relative uncertainty of E-7. This will enable top industrial calibration services to reduce their uncertainties by a factor of about 100.

Abstract (Englisch)

The aims of the project have been fully reached. A prototype of the modular system for the calibration of capacitance standards based on the quantum Hall effect was successfully realized and is now in operation at the Physikalisch-Technische Bundesanstalt (PTB). This bridge allows the calibration of a 10 pF capacitor with an uncertainty of about on part in 10⁷. A similar system is now in phase of development at METAS.

The other results of the project can be summarised as follows:

• A comprehensive and detailed study of the parameters influencing the characteristics of QHE devices used in metrology was carried out. A set of recommendations was established which will help to improve the quality of QHE devices for metrological applications in the future.
• The techniques necessary for the successfull measurement of the quantized Hall reistance at audio frequencies were refined and put in operation. The proper mounting techniques for the QHE devices were developed.
• A systematic investigation of the current and frequency dependence of the Hall reistance R_H and the longitudinal resistance R_xx was carried out on different QHE devices. The deviation of the quantum Hall resistance from the von Klitzing constant is found to be proportional to the longitudinal resistance. The difference extrapolates to zero, within the measurement uncertainty, when the dissipation in the two-dimensional electron gas vanishes.

Umsetzung und Anwendungen (Englisch)

The QHE sample holder for AC measurements developed within the framework of this project has been proposed to other laboratories through a EUROMET project (Nr. 540). The standardisation of this important piece of equipment facilitates the sample exchange and increases the synergy between National Metrology Institutes.

A 12.906 kO AC transfer standard was developed. The device has a modular design which facilitates the modification of the nominal value of the resistor. The standard is commercially available and can be used for various applications in impedance metrology.

The knowledge on coaxial ac bridges gained during this project is a key component of the success of the realization of the R-C chain presently under development at METAS.

Finely, the proportionality between the deviation of the quantum Hall resistance from the von Klitzing constant and the dissipation would lead to the possibility to use the ac quantum Hall resistance as primary standard of ac resistance.

Publikationen / Ergebnisse (Englisch)

Publications in scientific journal

B. Jeckelmann, A. Rüfenacht, B. Jeanneret, F. Overney, K. Pierz, A. von Campenhausen and G. Hein, Optimization of QHE devices for metrological applications, IEEE Trans. Instrum. Measure. 50, 218 (2001).

J. Melcher, J. Schurr, K. Pierz, J.M. Williams, S.P. Giblin, F. Cabiati, L. Callegaro, G. Marullo-Reedtz, Ch. Cassiago, B. Jeckelmann, B. Jeanneret, F. Overney, J. Bohacek, J. Riha, O. Power, J. Murray, M. Nunes, M. Lobo, I. Godinho, The European ac-QHE project: modular system for the calibration of capacitance standard based on the quantum Hall effect, IEEE Trans. Instrum. Measure. 52, 563 (2003).

 F. Overney, B. Jeanneret and B. Jeckelmann, Effects of metallic gates on ac measurements of the quantum Hall resistance, IEEE Trans. Instrum. Measure. 52, 574 (2003).

 

F. Overney, B. Jeanneret, B. M. Wood and J. Schurr, Influence of the Dissipation in ac Measurements of the Quantized Hall Resistance, IEEE Trans. Instrum. Measure. 54, 658 (2005).

 

J. Schurr, B. M. Wood and F. Overney, Linear Frequency Dependence in ac Resistance Measurement, IEEE Trans. Instrum. Measure. 54, 512 (2005).

 

J. Bohácek, EUROMET Project 432: Frequency performance of 12 906 O and 6453 O reference resistors for ac quantum Hall effect experiments, Metrologia, vol. 39, 231, (2002).

 

Conference contributions

B. Jeckelmann, Optimization of QHE devices for metrological applications, Conference on Precision Electromagnetic Measurements, Sydney, May 2000

 

B. Jeckelmann, DC characterization of QHE devices, Workshop AC-QHE, PTB Braunschweig, 29-30 October 2001.

 

F. Overney, AC measurements of the quantized Hall resistance at METAS, EUROMET electricity and magnetism, DC and quantum metrology: expert meeting, Bratislava, 16 June 2003.

 

F. Overney, NRC-METAS-PTB collaboration, part 3: frequency, current and field dependence in the quantized Hall and longitudinal ac resistance, Conference on Precision Electromagnetic Measurements, London UK, June 2004

 

F. Overney, Calibration of 10 pF in terms of R_K and uncertainty budget, EUROMET electricity and magnetism, DC and quantum metrology: expert meeting, METAS, May 2005.

 

F. Overney, Summary of results from METAS/PTB/CNRC cooperation, EUROMET electricity and magnetism, DC and quantum metrology: expert meeting, METAS, May 2005.