1 V programmable voltage standards based on SNIS Josephson junction series arrays

Abstract

Binary-divided 1 V arrays were fabricated for programmable Josephson voltage standards in close cooperation between INRIM and PTB. The arrays, consisting of 8192 overdamped Nb/Al–AlOxNb SNIS Josephson junctions, were successfully operated at microwave frequencies around 70 GHz. While the characteristic voltage of the junctions ranged from 0.25 to 0.6 mV, the current margins were larger than 1 mA for the Shapiro step n = 1. In addition, flat Shapiro steps of higher order (n = 3 and 4) were generated at increased microwave power levels due to the large characteristic voltage, demonstrating the small parameter spread of the SNIS junctions. Operation at temperatures up to 6–7 K has also been verified, measuring quantized voltages up to 1.25 V on the n = 1 step.

Universality of transport properties of ultrathin oxide films

“…One of the ways of checking it is to detect Shapiro steps in the I -V curves under microwave irradiation. Our experiments on SNIS single junctions rf radiated with a frequency of 73.5 GHz have displayed a clear harmonic step structure in the current-voltage characteristics up to 8.3 K without any subharmonic features [30]. In the inset of figure 2 we show Shapiro steps at T = 6.3 K for binary divided series arrays of 8192 Josephson SNIS junctions with d Al = 110 nm, a part of the samples used for subgap resistance measurements.…”

Temperature Stability of SNIS Josephson Arrays Between 4.2 K and Critical Temperature in Cryocooler

“…We measured segments from 1 to 8192 junctions of SNIS arrays fabricated in cooperation with the Physikalisch Technische Bundesanstalt (PTB) [16]. For testing purposes chips were fabricated with different parameters.…”

“…Metrological evaluation of the step profile with microvolt resolution was also performed [16] up to 1.25 V at 6.5 K.…”

Intrinsically shunted Josephson junctions for electronics applications

“…Even moreover, they have showed the possibility of operation at 4.2 K being biased on a higher order step and therefore can potentially reduce the number of junctions on the chip as well as an operation at higher temperatures, up to 6-7 K employing energy efficient cryocoolers [72].…”