Dependence of the substrate structure and the film growth at the junction of YBCO SEJ rf-SQUIDs on the IBE process and effects on the SQUID's characteristics

Date
2002
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Source Title
Physica C: Superconductivity and its Applications
Print ISSN
0921-4534
Electronic ISSN
Publisher
Elsevier
Volume
372-376
Issue
Pages
240 - 244
Language
English
Type
Article
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Abstract

Step edge junction (SEJ) rf-SQUIDs were made of 200 nm thick YBCO films on LaAlO3(100) substrates using pulsed laser deposition technique. The steps on the substrates were developed using a combination of stationary and rotating angled argon ion beams with different beam energies and intensities. While sharp clean steps with heights up to 300 nm were obtained on the substrates using the combinatorial ion beam etching (IBE) process, very shallow ramp-type surfaces were found developing on the bottom of the trench, close to the steps. The ramp-type surfaces were found to be a source of hole-type defects in the films grown at the step edges. High quality films could be obtained on the flat regions away from the steps. Higher defect densities in the films close to the SEJs resulted in devices with higher 1/f noise and wider spread of the junction parameters. The 1/f noise of such devices increased with decreasing temperature. High quality films on sharp clean steps with flat substrate surfaces, developed using optimized combinatorial IBE process, resulted in higher yield of low 1/f noise SQUIDs. The Ic of the junctions and hence the working temperature of the SQUID could also be controlled by the junction width and the step height.

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Keywords
1/f noise, rf-SQUID, Step edge Josephson junction, YBCO thin film, Etching, Film growth, Grain boundaries, Ion beams, Josephson junction devices, Microstructure, Pulsed laser deposition, Semiconductor junctions
Citation
Published Version (Please cite this version)