Low-frequency excess noise in Nb-Al2O3-Nb Josephson tunnel junctions

Abstract

A fabrication technique for Nb‐Al₂O₃‐Nb Josephson tunnel junctions is described that is an alternative to the trilayer method generally used. At 4.2 K the magnitude of the low‐frequency noise in the critical current I₀ of four junctions with areas A ranging from 7.8 to 115 μm² was characterized by S^1/2I₀ A^1/2/I₀ =(14±6)pA μm/μA Hz^1/2, where SI₀ is the spectral density of the excess noise at 1 Hz. The noise power spectrum of one 3×3 μm² junction exhibited a Lorentzian feature associated with the emptying and filling of a single trap in the barrier. The low level of noise makes these junctions attractive for use in superconducting quantum interference devices.