Critical current densities in superconducting granular Al-Al-20-3 films

This paper reports measurements of the critical current densities on thin granular superconducting Al-A1-20-3 films as a function of the normal state resistivity of the granular material and as a function of temperature. It is observed that the Al-Al-20-3 films exhibit critical current densities of 102A/cm2 to 103 A/cm2 over a broad range of normal state resistivities ranging from 30 µΩcm to 3000 µΩcm; the critical current density is inversely proportional, approximately to the square root of the normal state resistivity, and in most cases, is directly proportional to (1 − T/Tc). SQUID quantum devices having very large widths of 10 µm to 25 µm have been prepared from these very low critical current films.