Fabrication of Hot Phonon Controlled-Junction microSQUID

Abstract

We report on the design and nano-fabrication of a controlled micron-sized direct current superconducting quantum interference device (microSQUID). These devices integrate a critical current control mechanism, fabricated as a self-aligned structure, with two Dayem Bridge type Josephson junctions (length of ~200nm and width ~100nm). These junctions are controlled by hot phonons from nearby titanium normal metal constrictions (‘heaters’) that are current biased; the hot phonon flux provides an efficient cooper pair breaking mechanism. The implementation of a controlled Josephson junction provides a way for the modification of the junction characteristics post-fabrication. The devices were measured at a temperature of 4.2 K and control over the critical current oscillations was observed: demonstrating the ability to manipulate the characteristics of the microSQUID.