A capacitance standard based on counting electrons

Science

Volumn 285, Issue 5434, 1999, Pages 1706-1709

  Keller, Mark W ^a   Eichenberger, Ali L ^a   Martinis, John M ^a   Zimmerman, Neil M ^a  

^a NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ARTICLE; ELECTRIC POTENTIAL; ELECTRODE; ELECTRON TRANSPORT; PRIORITY JOURNAL; QUANTUM MECHANICS;

EID: 0033543512     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.285.5434.1706     Document Type: Article

References (22)

1. B. N. Taylor, Ed., The International System of Units (SI), NIST Spec. Publ. 330 (Government Printing Office, Washington, DC, 1991) (available at http://physics. nist.gov/Document/sp330.pdf).
2. B. N. Taylor and T. J. Witt, Metrologia 26, 47 (1989).
3. The 1990 volt and ohm have not been formally integrated into the SI, but they are in use worldwide as practical units because they can be reproduced with much smaller uncertainty than the SI volt and ohm.
4. W. K. Clothier, Metrologia 1, 36 (1965).
5. H. Grabert and M. H. Devoret, Eds., Single Charge Tunneling (Plenum, New York, 1992).
6. E. R. Williams, R. N. Ghosh, J. M. Martinis, J. Res. Natl. Inst. Stand. Technol. 97, 299 (1992).
7. N. M. Zimmerman, Am. J. Phys. 66, 324 (1998).
8. M. W. Keller, J. M. Martinis, N. M. Zimmerman, A. H. Steinbach, Appl. Phys. Lett. 69, 1804 (1996).
9. M. W. Keller, J. M. Martinis, A. H. Steinbach, N. M. Zimmerman, IEEE Trans. Instrum. Meas. 46, 307 (1997).
10. N. M. Zimmerman, ibid. 45, 841 (1996).
11. _, J. L. Cobb, A. F. Clark, ibid. 46, 294 (1997).
12. H. Pothier, P. Lafarge, C. Urbina, D. Esteve, M. H. Devoret, Europhys. Lett. 17, 249 (1992).
13. We fabricated these structures by evaporating Al through a suspended polymer mask that was patterned with electron beam lithography. We deposited Al from one angle, oxidized it to form an insulating layer, and then deposited a second layer of Al from a different angle so that it partially overlaps the first layer. This forms metal-insulator-metal sandwiches in the overlapping regions, and the insulator is thin enough to allow quantum tunneling.
14. Although an electron pump can be made with as few as three junctions, we used seven junctions in order to suppress undesired multijunction tunneling events that are rare but not negligible at temperatures well below the charging energy barrier.
15. We focus here on electron counting, but the pump is also an accurate current source. The maximum current of ≈10 pA is too small for conventional metrology, but it can be useful in situations where accurate measurements of extremely small currents are needed.
16. Thermal cycling to room temperature between these two experimental runs caused C to change by ≈2% because of mechanical changes in the capacitor. Unlike an artifact, the SET standard is not affected by this change because C is determined in situ each time the standard is cooled and operated.
17. Throughout this report, we use expanded uncertainty with coverage factor k = 2, which defines an interval that is expected to contain ≈95% of the reasonable values for the measured quantity.
18. We used a digital voltmeter that was calibrated with a Josephson voltage standard and has a relative uncertainty of 0.1 ppm for its range of 10 V. The finite input current of the voltmeter is supplied by the feedback circuit and does not affect the measurement of ΔV.
19. E. R. Cohen and B. N. Taylor, Rev. Mod. Phys. 57, 1121 (1987).
20. We used commercial capacitance bridge model AH2500A (Andeen-Hagerling, Cleveland, OH). The identification of specific commercial instruments does not imply endorsement by NIST nor does it imply that the instruments identified are the best available for a particular purpose.
21. The authors gratefully acknowledge voltage calibration assistance from C. Hamilton, capacitance calibration assistance from A.-M. Jeffery, and discussions with E. Williams regarding Eq. 2.
22. May 1999; accepted 29 July 1999