Operating Margins of a 10 V Programmable Josephson Voltage Standard Circuit Using ${\rm NbN}/{\rm TiN}_{x}/{\rm NbN}/{\rm TiN}_{x}/{\rm NbN}$ Double-Junction Stacks

Abstract

The operating margins of a 10 V programmable Josephson voltage standard circuit using Operating margins of a 10 V programmable josephson voltage standard circuit using NbN/TiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /NbN/TiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /NbN double-junction stacks was investigated as a function of microwave frequency and operating temperature. The circuit contained 32 arrays of 5 120 Operating margins of a 10 V programmable josephson voltage standard circuit using NbN/TiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /NbN/TiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /NbN double-junction stacks. In other words, the circuit contained 327 680 Operating margins of a 10 V programmable Josephson voltage standard circuit using NbN/TiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /NbN/TiN <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /NbN junctions. It was found that the operating margins (the heights of the constant-voltage step) of the arrays varied largely with microwave frequency and operating temperature. The microwave-frequency dependence was due to the resonance of the microwaves in the circuit. The temperature dependence of the circuit was due to the temperature dependence of the I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> product of the junctions, where I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> was the critical current R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</sub> and was the normal resistance. Fortunately, however, the operating margin was maximized by changing the temperature of the chip, mounted on the cold head of a cryocooler.