Prospects for proximity effect superconducting FETs

The authors address the question of how a JOFET (Josephson field effect transistor) works and whether or not a useful device of this type is feasible. They show that JOFETs represent a limiting case of normal FETs in which superconducting source and drain contacts result in zero channel resistance. This results in improved device characteristics, but does not have a major effect on speed or power dissipation. With conventional superconductors, the input and output voltage scales are incompatible, but the authors describe the extent to which this can be overcome by using high-temperature superconductors, making possible voltage gain exceeding unity. Device length and operating temperature are constrained by the natural length scale for the penetration of superconductivity into normal materials, so that submicrometer device dimensions and operating temperatures less than approximately 77 K are required. Silicon is effectively ruled out in favor of III-V materials for device operation above approximately 20 K.>