Josephson device for voltage measurement

Abstract

This paper describes a new Josephson device with microwave integrated circuit for voltage standard. The circuit is essentially made of a resonator (Nb), the Josephson junction (Nb, NbOx, Pb-In) and a capacitive microstrip section (Pb-In) which ends the rf part; the dc connections are through Cauer Filters (Nb or Pb-In). A niobium film is deposited on the opposite side of the fused quartz substrate as a ground plane. The circuit is enclosed in a special package with outside dc and rf connections. The technology ensures very good cyclability and lifetime with storage at room temperature. In liquid helium (4.2 K) with a very weak rf power less than 0.5 milliwatts at the frequency resonance (11.5 GHz), 100 μ A high current steps were obtained near a polarization of 4.5 mV. These devices allows a precision of 1 × 10 −7 on the volt standard when used with a series-parallel divider of fixed value (ratio 225). The precise adjustment of the voltages is made by a slight drift of the rf frequency of the source, allowed by the high rf coupling factor of the device and the band width of its resonance.