Optimum deposition condition of Nb/Al multilayers for large-scale array detectors with superconducting tunnel junctions

Chen, Y.; Ukibe, Masahiro; Kurokawa, A.; Fujimoto, Takashi; Ohkubo, M.

doi:10.1016/j.physc.2008.05.283

Cited by 5 publications

(2 citation statements)

References 16 publications

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“…In our experiments, the standard deviation of the Ar gas pressures was . The Si substrate was cleaned by the recipe described in detail elsewhere before film deposition [6]. The Nb films with a thickness of 400 nm were deposited at a DC current of 1.2 A.…”

Section: A Residual Stress Evaluationmentioning

confidence: 99%

“…Since the thickness of the tunneling barrier is as thin as 1 nm, the quality of the tunneling barrier can be easily affected by the surface conditions of the sputtered Nb and Al films. The dependence of the surface morphology on the deposition conditions and the pre-treatment of the silicon substrate before the film deposition have been evaluated by using an atomic force microscope (AFM) [6].…”

Section: Introductionmentioning

confidence: 99%

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Characterization of Nanometer Step Structure Formation During the Fabrication of Large-Scale Superconducting-Tunnel-Junction Array Detectors

Ukibe

Kurokawa

Ohkubo

2009

IEEE Trans. Appl. Supercond.

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Superconducting-tunnel-junction (STJ) array detectors with an effective sensitive area of 4 mm 2 were fabricated for mass spectrometry. An array detector has one hundred Nb Al AlO Al Nb junctions with a 200 m-square sensitive area. The junctions are quasi-horizontally arranged on a 10 mm-square chip. In the course of fabrication processes, we have found that an anomalous nanometer-step structure appears within the junctions located in the outer region of the array detectors at a specific stage of the fabrication processes. The anomalous steps cause an increase of the leakage current from 5 nA to a few 100 nA. In order to characterize and prevent the step structure formation, we performed structural analyses with atomic force microscopy, interference microscopy, differential interference contrast microscopy, and transmission electron microscopy. Vertical fault and blister formations were identified in the junctions around the periphery of the array arrangement even on a low stress sputtering condition of 40 MPa. In addition, it is reasonable that a horizontal slip in the AlO barrier layer is induced by a nanoscale plastic deformation, which causes the large increase of the leakage current.

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Section: A Residual Stress Evaluationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%