High-TcSNS dc SQUIDs produced by electron beam lithography

We have utilized electron beam lithography to fabricate dc SQUIDs incorporating Nb3Ge/Cu/Nb3Ge step-edge microbridges. The primary advantage of this process, over conventional lithography, is to decrease the width of the microbridges and hence increase their normal resistance. The microbridges produced typically have normal resistances between 0.1-1.0 Ω, and we have investigated the behavior of the resistance as the width is scaled down. The dc SQUIDs operate without hysteresis over a wide temperature range and exhibit substantial critical current modulation in the presence of a magnetic field, from which we estimate the inductance of the SQUIDs to be about 13 pH. These devices should possess extremely low self-heating effects by virtue of the two-dimensional geometry of the banks made possible by the use of a novel ion beam etching technique. Preliminary noise measurements indicate an intrinsic energy sensitivity as low as 3 h at 2.2 K.