ИСТИНА

Magnetic flux trapping degrades the performance and in extreme cases makes superconducting digital circuits completely nonoperational. This parasitic effect can be partly kept under control by a reduction of the residual field. However, the best known protection tool is cutting long narrow openings (moats) in wide superconductor thin films. It is supposed that the undesirable residual magnetic field is frozen in the dedicated moats instead of being frozen in vortices randomly distributed along the film. In other words, the moats serve as landfills, i.e. they immobilize vortices by converting them into quantized fluxes frozen in the moats. So far intuition plays a more significant role than science in the selection of geometry and density of the moats. We have developed a rigorous procedure for calculation of Gibbs potentials for arbitrary shaped films exposed by magnetic fields. In particular, this procedure allows the potentials with and without vortices and/or fluxes frozen in moats to be compared. We numerically simulated evolutions of Gibbs potentials of slowly cooled films exposed to constant residual magnetic field. The real distribution of vortices and fluxes trapped in the moats should correspond to those with the lowest Gibbs potential. The superconductor film is immune to the trapping of Pearl vortices if the lowest Gibbs potential is achieved without such vortices. Vice versa, if the lowest Gibbs potential results in a flux pattern with trapped vortices, we know that the geometry and density of moats at the given residual magnetic field are not suitable for microelectronics application. We also discuss how to convert the proposed approach into a routine CAD procedure.