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Josephson Gate Gain Curve Side Lobes Reduction

IP.com Disclosure Number: IPCOM000083978D
Original Publication Date: 1975-Aug-01
Included in the Prior Art Database: 2005-Mar-01
Document File: 2 page(s) / 22K

Publishing Venue

IBM

Related People

Baechtold, W: AUTHOR [+3]

Abstract

A Josephson gate control characteristic usually shows "side lobes" i.e., secondary maxima of the gain curve which are caused by the higher order vortex modes (see Fig. A). For some circuit applications it is useful to have a gate characteristic, in which the amplitude of the first (1-2) and higher order vortex modes is small (see Fig. B). This can be achieved by tailoring the Josephson junction. The DC Josephson current versus magnetic-field characteristic of tunneling junctions is influenced by the junction shape and by variation of the local current density.

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Josephson Gate Gain Curve Side Lobes Reduction

A Josephson gate control characteristic usually shows "side lobes" i.e., secondary maxima of the gain curve which are caused by the higher order vortex modes (see Fig. A). For some circuit applications it is useful to have a gate characteristic, in which the amplitude of the first (1-2) and higher order vortex modes is small (see Fig. B). This can be achieved by tailoring the Josephson junction. The DC Josephson current versus magnetic-field characteristic of tunneling junctions is influenced by the junction shape and by variation of the local current density.

Vortex modes can be greatly reduced in amplitude, by either shaping the junction so that the area in the center region is greater than at the ends or/and by tailoring the current density to have a maximum in the center of junction. The latter can be achieved by lateral diffusion into the junction after fabrication.

Other approaches during junction fabrication comprise either selective ion implantation or selective oxide formation, by influencing RF oxidation with electron optical means. Application of a DC bias to, e.g., a metal mask surrounding the junction during RF oxidation, acts like an electrostatic lens to control the distribution of ions striking the surface, and hence vary the relative oxidation and sputtering rates.

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