Journal of Materials Research
November 2005— Volume 20, Number 11

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Aluminum nitride tunnel barrier formation with low-energy nitrogen ion beams Anupama B. Kaul, Alan W. Kleinsasser, Bruce Bumble, Henry G. LeDuc, and Karen A. Lee Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109

We report the use of low-energy nitrogen ion beams to form ultra-thin (<2 nm) layers of AlN_x to act as tunnel barriers in Nb/Al-AlN_x/Nb Josephson junctions. We fabricated reproducible, high-quality devices with independent control of the ion energy and dose, enabling exploration of a wide parameter space. Critical current density J_c ranged from 550 to 9400 A/cm² with subgap-to-normal resistance ratios from 50 to 12.6. The spatial variation of ion-current density was roughly correlated with J_c over a large-area on a Si substrate. The junctions were stable on annealing up to temperatures of at least 200 °C. This technique could be applied to form other metal nitrides at room temperature for device applications where a high degree of control is desired.

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