Thin Films of Niobium for Cryotron Ground Planes

A process is described for the vacuum deposition of thin films of superconductive niobium for use as electrical ground planes in cryoelectric circuitry. High-purity niobium films are deposited onto glass and aluminum substrates by evaporation from a focused electron-beam-heated source. The deposition process is described in detail, and the influence of substrate temperature on film purities is discussed. A pinhole-free insulation between 1000–3000 Å is formed on the niobium films by anodization, and the surface roughness of the niobium is examined with an electron microscope as a function of oxide thickness. The superconducting properties of the niobium films are described in terms of their critical temperature, lattice parameter, resistance ratio, critical currents of shielded Sn films, and their ability to resist flux trapping.