High Performance DC Superconducting Quantum Interference Device Utilizing a Bicrystal Junction with a 30° Misorientation Angle

Abstract

A high T c dc superconducting quantum interference device (SQUID) was fabricated using a bicrystal junction with a misorientation angle of θ=30°. The junction with a width of 2 µ m exhibited high resistance R s=10 Ω and critical current I0=25 µ A at T=77 K. This gives a I0R s as high as 250 µ V. These values indicate that the bicrystal junction has great potential for the development of high performance SQUIDs. The SQUID fabricated with a 30° junction exhibited voltage modulation depths as high as ΔV=85 µ V, 40 µ V and 20 µ V at T=77 K for the inductance values of L s=60 pH, 100 pH and 160 pH, respectively. These are the highest values reported so far. Preliminary noise measurement showed that the flux noise of the SQUID is less than 8 µΦ0/ Hz1/2 for the white noise region, and less than 70 µΦ0/ Hz1/2 at f=1 Hz when the 60 pH-SQUID is dc biased and operated with a conventional Flux Locked Loop (FLL) circuit.