Thin-Film Cryotrons: Part I-Properties of Thin Superconducting Films

This paper, consisting of three parts, describes the thin-film cryotron. This device, constructed by vacuum deposition of layers of lead, tin and silicon monoxide, is considerably smaller and faster than its wire-wound predecessor. Part I describes the characteristics of evaporated superconductive films as they apply to cryotrons. Their current-carrying capacity has been found to be proportional to width and proportional to thickness when the film is thinner than twice the penetration depth. Thermal effects caused by poor heat transfer to the bath distort the data, and the use of quartz substrates and low duty cycle pulse measurements help to reduce this distortion. The function of a superconductive reflector or ground plane under a film is discussed. The current-carry ing capacity of such a film is increased because of effective cancella tion of the normal component of magnetic field.