Anomaly in Fabrication Processes for Large-Scale Array Detectors of Superconducting Tunnel Junctions

Ukibe, Masahiro; Chen, Y.; Shimizugawa, Y.; Kobayashi, Yohei; Kurokawa, A.; Ohkubo, M.

doi:10.1007/s10909-007-9650-0

Cited by 10 publications

(9 citation statements)

References 2 publications

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“…In addition, our previous work [3] elucidated that the low reproducibility of the leakage currents is mainly caused by the stepped surface structure of the STJs shown in Fig. 1 and that stepped surface structure is formed by the residual stress of the sputtering films of the STJs.…”

Section: Introductionmentioning

confidence: 92%

“…For real applications, the detector size should be large enough to obtain a good statistic for a short measurement time with keeping an excellent energy resolution. Therefore, we fabricated a detector array with a size of 4 mm 2 consisting of a hundred of STJ elements, which have a size of 200 Â 200 lm 2 and critical current density (J c ) of about 200 A/cm 2 [3,4]. However, the operation yield, i.e., the number of elements in 100 STJs with low leakage currents less than 1 lA at a bias voltage near D/e and 0.35 K, varied from 20% to 85% in different fabrication runs [3].…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, we fabricated a detector array with a size of 4 mm 2 consisting of a hundred of STJ elements, which have a size of 200 Â 200 lm 2 and critical current density (J c ) of about 200 A/cm 2 [3,4]. However, the operation yield, i.e., the number of elements in 100 STJs with low leakage currents less than 1 lA at a bias voltage near D/e and 0.35 K, varied from 20% to 85% in different fabrication runs [3]. In order to utilize the 100 STJ array detectors for practical use, it is necessary to achieve an operation yield over 90% and a high reproducibility of STJ characteristics, which means that all available STJ elements in an array have a constant leakage current as low as possible.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

Chen

Ukibe

Kurokawa

et al. 2008

Physica C: Superconductivity

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Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Chen

Ukibe

Kurokawa

et al. 2008

Physica C: Superconductivity

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“…The STJ detector fabrication details can be found in Ref. 13. The STJ detector has a mass-independent sensitivity and an efficiency of 100% up to more than 1 MDa for ions of a few keV.…”

Section: Charge-state Discriminating Superconducting Detectorsmentioning

confidence: 99%

Kinetic‐energy‐sensitive mass spectrometry for separation of different ions with the same m/z value

et al. 2008

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A double-focusing mass spectrometer (MS) equipped with a superconducting-tunnel-junction (STJ) detector has been applied to measure relative ionization cross-sections for the production of ions that are accompanied by different ion species with the same mass-to-charge (m/z) value. The STJ detector fabricated for this study enables kinetic energy (E) measurement of incoming individual ions at a counting rate of up to approximately 100 k ions/s and an energy resolution (DeltaE/E) of 15%. Both high counting rate and high-energy resolution are necessary to independently determine both m and z and not the m/z value only in ion-counting MS experiments. Ions such as (14)N(2) (2+) and (14)N(+) with the same m/z value can be clearly discriminated using a kinetic-energy-sensitive MS. This fine discrimination capability allows direct determination of relative ionization cross-sections of the homonuclear diatomic ions (14)N(2) (2+)/(14)N(2) (+) and (16)O(2) (2+)/(16)O(2) (+), which are difficult to measure due to the strong interference by the signals of their dissociated atomic ions with noticeably large ionization cross-sections. The new instrument requires no low-abundance heteronuclear diatomic molecules of the forms (14)N(15)N or (16)O(17)O to carry out ionization studies and thus, is expected to be useful in fields such as atmospheric science, interstellar science, or plasma physics.

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“…Although superconducting detectors enable charge state discrimination through kinetic energy measurement as well as TOF, one of the disadvantages of STJ detectors is their small sensitive area for molecules. In order to realize a practical detector size that is necessary to obtain a good statistic for high-throughput MS analysis without degradation of the energy resolution, therefore, we fabricated an array detector with a size of 4 consisting of one hundred Nb-based STJs, each of which has a size of [3], [4]. The leakage currents of STJs ranged from 1 nA (0.025 ) to several .…”

Section: Introductionmentioning

confidence: 99%

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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Anomaly in Fabrication Processes for Large-Scale Array Detectors of Superconducting Tunnel Junctions

Cited by 10 publications

References 2 publications

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

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

Kinetic‐energy‐sensitive mass spectrometry for separation of different ions with the same m/z value

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

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