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M. Ukibe , Y. Chen, Y. Shimizugawa, Y. Kobayashi, A. Kurokawa, M. Ohkubo

M. Ukibe , Y. Chen, Y. Shimizugawa, Y. Kobayashi, A. Kurokawa, M. Ohkubo National Institute of Advanced Industrial Science and Technology(AIST), Research Institute of Instrumentation Frontier,.

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M. Ukibe , Y. Chen, Y. Shimizugawa, Y. Kobayashi, A. Kurokawa, M. Ohkubo

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  1. M. Ukibe, Y. Chen, Y. Shimizugawa, Y. Kobayashi, A. Kurokawa, M. Ohkubo National Institute of Advanced Industrial Science and Technology(AIST), Research Institute of Instrumentation Frontier, Anomaly in fabrication processes for large-scale array detectors of superconducting tunnel junctions

  2. Nb 100nm Goal:～90% with uniform IV characteristics Al:50nm Al:50nm Nb 100nm Development of 100 STJ array detector • Task 11mm fabrication yield 85%<1mA@0.4mV Wide Distribution of the leak current in 100 STJ array 1nA ～1μA

  3. Leak currents of STJ elements Low leakage STJ : Center part of a 100 array Large leakage STJ: Outer part of a 100 array Leak current level Isub<150nA:good 150nA<Isub<1000nA 1000nA<Isub Point contact Open Short

  4. Causes the leak current ? After etching of bottom Nb layers Stepped surface! In the outer part of a 100 array Same with the the leak currents

  5. Stereograph of surface of STJs

  6. Stress Free Nb film ? Origin of the stepped surface？ After the bottom Nb RIE Almost Nb layer on wafer is removed Change of the stress condition between Nb/Allayer and wafer Defects in the tunnel barrier ? Origin of the leak currents？

  7. Displacement of curve of Si wafer at each steps Top and Bottom Al wet etch Bottom Nb RIE

  8. Limited etching Two processesfor removing the stepped surface Decrease of the stress displacement of Nb/Al films during the process Decrease of the etched Nb/Al area Liftoff of Nb/Alfilms Liftoff method Start Start Keep curve Keep curve End End

  9. Large stepped surface Small stepped surface Perfect surface Improvement of leak currents Leak current : positive correlation to stepped surface area size

  10. Start Keep curve End Conclusions Distribution of leak current: 1nA ～1mA Distribution of stepped surface Variation of the curve of Nb/Al and the wafer In case of a large–size STJ array over the size of ～mm2 Even stress free films has big influence!! High fabrication yield and reproducibility

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