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IEEE Transactions on Instrumentation and Measurement

Hybrid integration of a Josephson series array and a 10 GHz planar oscillator

Franz X. Hebrank, E. Vollmer, Torsten Funck, J. Kohlmann, P. Gutmann, J. Niemeyer

Published Apr 1, 1997• 1 citation
Publisher

Abstract

A computer-controlled Josephson voltage standard has been developed comprising the hybrid integration of a planar oscillator and a Josephson series array. A 10 GHz voltage controlled oscillator has been frequency-stabilized to a reference frequency by a phase-locked loop. A series array has been designed and fabricated in Nb/Al/sub 2/O/sub 3//Nb technology. To obtain quantized voltage steps with a drive frequency of 10 GHz, the critical current density of the Junctions is reduced to below 2 A/cm/sup 2/ by variation of the oxidation parameters. The hybrid integration of a Josephson circuit with a planar MESFET oscillator produced quantized voltage steps up to 980 mV with a step width of 2 /spl mu/A.

DOI
10.1109/19.571822

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A computer-controlled Josephson voltage standard has been developed comprising the hybrid integration of a planar oscillator and a Josephson series array. A 10 GHz voltage controlled oscillator has been frequency-stabilized to a reference frequency by a phase-locked loop. A series array has been designed and fabricated in Nb/Al/sub 2/O/sub 3//Nb technology. To obtain quantized voltage steps with a drive frequency of 10 GHz, the critical current density of the Junctions is reduced to below 2 A/cm/sup 2/ by variation of the oxidation parameters. The hybrid integration of a Josephson circuit with a planar MESFET oscillator produced quantized voltage steps up to 980 mV with a step width of 2 /spl mu/A.
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A programmable dc voltage standard for output voltages of up to 10 V has been realized. The series arrays, consisting of about 69120 overdamped superconductor/insulator/normal metal/insulator/superconductor (SINIS) Josephson junctions, have been fabricated using the reliable Nb-Al/Al/sub 2/O/sub 3/ technology. The arrays can be operated in conventional Josephson voltage standards at microwave frequencies from 70 GHz to 75 GHz. Steps of constant voltage are observed at very low microwave power levels, since the major part of the microwave power is generated by the junctions themselves. The operation of the arrays and the formation of Shapiro steps are discussed.