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We fabricated a niobium (Nb) Josephson junction with a hafnium (Hf) overlayer. The Hf native oxide (HfOx), formed by thermal oxidation, was used as the new tunneling barrier. Hf was selected as an overlayer because of its good affinity to Nb and strong oxygen affinity. The junction was fabricated the same way as Nb/AlOx-Al/Nb junctions. The junction showed excellent I-V characteristics (Vm=40 mV and Vg=3.0 mV). The critical current of the junction did not change with annealing up to 250 °C.
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Morohashi et al. (1992) studied this question.
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