Progress in measurements of a single-electron pump by means of a CCC

This paper deals with the improvements of the BNM-LNE experimental setup based on a cryogenic current comparator (CCC) devoted to the high-accuracy measurement of current delivered by a single-electron tunneling pump. A three-junction Cr-Al R-pump, fabricated by the PTB, has been fully characterized. First current steps have been observed at pumping frequencies up to 30 MHz. At 10 MHz, for which I = 1.6 pA, the current step is found to be flat within +/-15 fA (5 min of measurement) over a bias voltage range of 200 muV. At the middle of the step, currents of a few pA have been measured with a type-A uncertainty as low as 12 aA which results from a 12-h measurement. Although the CCC has not been used in its optimal operating mode, the results demonstrate the possibility to measure the current generated by a single-electron tunneling pump with type-A uncertainties as low as a few parts in 10(6).