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IEEE Transactions on Applied Superconductivity

Investigation of Temperature Dependence of Microwave-Induced Characteristics of a NbN Josephson Junction Array

Alexandre Shoji, Hiroshi Takashima, M. Murugesan, Haruhiko Obara, Hirotake Yamamori

Published Jun 1, 2005• 1 citation
Publisher

Abstract

To investigate the temperature dependence of microwave-induced characteristics of a NbN Josephson junction array, the surface resistance, R/sub s/, of NbN films was measured using the dielectric resonator method at 22 GHz and temperatures from 5.8 K to 14.8 K. From the measured R/sub s/ values, the attenuation of 16 GHz microwaves in a NbN coplanar waveguide was calculated and constant-voltage-step amplitude for a NbN junction array biased with a DC current and 16 GHz microwaves was calculated as a function of temperature, resulting in a theoretical temperature dependence of constant-voltage-step amplitude.

DOI
10.1109/tasc.2005.849755

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Microwave-Induced Characteristics of (NbN/TiNx)N/NbN{({\rm NbN/TiN}_{\rm x})}_{N}/{\rm NbN}(NbN/TiNx​)N​/NbN StackedJosephson Junction Arrays
Stacked (NbN/TiNx)N/NbN (N = 2, 3, 4, 5 and 10) Josephson junctions and their arrays have been fabricated on a Si chip and their microwave-induced characteristics were measured at a temperature around 10 K. To achieve a vertical and smooth edge of an NbN - TiNxmultilayer, an inductively coupled plasma reactive ion etching (ICP-RIE) technique was used. Current-voltage characteristics measured for stacks of (NbN/TiNx)N/NbN Josephson junctions without microwave indicated that critical currents for those junctions distribute in a certain range. We defined Ic- spread as (IcMAX- IcMIN)/IcAverage to measure the distribution of Ic. The Ic- spread was minimized when the thickness of intermediate electrodes was d = 50 nm. We also evaluated values of Ic- spread for stacks prepared at different fabrication runs as a function of the number of junctions in a stack N. As a result, we found N = 3 is the maximum for practical use. For arrays, we obtained a constant-voltage step height of about 2 m A for 2 048 stacks of double-barrier junctions (N = 2), and about 1 mA for 1 024 stacks of triple-barrier junctions (N = 3).
This paper presents the results of the measurements of 1-V Nb-AlO/sub x/-Nb, Josephson junctions arrays at temperatures 4.2-1.7 K in frequency band 54-80 GHz. The measurement of the temperature dependence of the critical current, gap voltage and subgap resistance of junctions is a useful tool for the quality control of arrays. By the measurements of the frequency dependence of array response to the microwave radiation it was found, that this response often has a resonance or interference like character, which is dependent on the array geometry. At the temperatures lower than 3-2.5 K as well as at low frequencies 54-60 GHz and T=4.2 K a transition to chaotic state of arrays was observed at small rf-power level.
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Operating Margins of a 10 V Programmable Josephson Voltage Standard Circuit Using NbN/TiNx/NbN/TiNx/NbN{\rm NbN}/{\rm TiN}_{x}/{\rm NbN}/{\rm TiN}_{x}/{\rm NbN}NbN/TiNx​/NbN/TiNx​/NbN Double-Junction Stacks
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