Selective Trilayer Ion-Beam Etching Process for Fabricating Nb/Nb Oxide/Pb-Alloy Tunnel Junctions
A new process, suitable for integrated circuits, for fabricating Nb/Nb oxide/Pb-alloy tunnel junctions is described. The process includes the following key steps: Nb/Nb oxide/Pb-alloy trilayer formation, involving in-situ thermal oxidation; junction area delineation by deep UV photolithography; highly selective Pb-alloy layer patterning by ion-beam etching; lift-off of an evaporated insulation layer. The fabricated junctions show good junction characteristics and excellent uniformity in critical currents. High-quality junctions with critical currents of about 80% of the theoretical values and without any knee structure have been obtained. Standard deviations in critical currents for 100 series-connected junctions with 4 × 4 and 2 × 2 µm areas are 0.8% and 2.4%, respectively. The junctions with Pbln and PbAuIn counterelectrodes exhibit sufficient thermal stability for this process.
KeywordsCritical Current Etch Rate Tunnel Junction Junction Area Photoresist Mask
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