Characteristics and Alternating Modulation of Y₁Ba₂Cu₃O_7-y Superconducting Flux Flow Transistors

The characteristics and the measurement of lower critical magnetic field of Y 1 Ba 2 Cu 3 O 7- y superconducting flux flow transistors (SFFTs) are reported. The devices are fabricated by forming the channels of vortex flow onto step edge of SrTiO 3 substrates. Reproducible transistor behaviors are observed, and the operation temperature is over 70 K. A method for measuring the lower critical field H ( c 1) from the magnetic field of both control current and bias current is also presented. We find that H ( c 1) of the Y 1 Ba 2 Cu 3 O 7- y SFFT is 0.9 G at 70 K using this method. Alternating modulation of the device is investigated, which shows transresistances of over 10 Ω and output resistances of about 5 Ω.