A hybrid cryotron technology: II--Fabrication

A hybrid thin-film cryotron fabrication technology utilizing a combination of stencil masking and photo-etching methods to achieve high-density (100 active devices per square centimeter) arrays of interconnected active devices is described. Stencil masks are used to delineate the superconducting shield plane, the cryotron gates, some interelement connections, and the intercircuit insulation. Photo-etching is used to form the uppermost layer of the cryotron array. This uppermost layer contains the most dimensionally critical segments of the circuit, the cryotron control elements and also the remainder of the device-to-device interconnections. Fabrication equipment has been developed for both laboratory and prototype manufacturing. Cryogenic test data collected from over 100 cryotron arrays, containing 1863 active interconnected devices per substrate, show that this hybrid fabrication process is consistently capable of producing substrates with elemental yields in excess of 99.9 percent. Substrates containing in excess of 10 000 active interconnected devices are now entering design, fabrication, and test.