Measurement of thermoelectric effects in a thermal converter using a NbN/TiN/NbN Josephson junction array

The AC-DC transfer difference due to thermoelectric effects in a thermal converter was evaluated using a NbN/TiN/NbN Josephson junction array as an ultra-stable fast-reversed DC (FRDC) source. The Josephson junction array was connected in parallel with a conventional semiconductor FRDC current source, as an "add-on" voltage-stabilizer for the input of the thermal converter. The AC-DC difference due to thermoelectric effects was evaluated with a standard measurement (type-A) uncertainty of the order of 0.01 /spl mu/V/V, four-times better than that with the conventional semiconductor FRDC source.

I. Introduction

The dc voltage standards are derived from the microwave-induced Josephson voltage steps. The amplitude of the voltage step is defined by the Josephson voltage-frequency relationship, , where is the total number of voltage steps, is the microwave frequency, and is the Josephson constant of 483 597.9 GHz/V.