Low Noise NanoSQUIDs Based on Deep Submicron Josephson Tunnel Junctions

In the recent years, it has been shown that the magnetic response of nano-objects (nanoparticles, nanobeads, and small cluster of molecules) can be effectively measured by using a Superconducting Quantum Interference Device (SQUID) with a small sensitive area. Here, we present high sensitivity nanoSQUIDs based on deep submicrometer Josephson tunnel junctions fabricated by a Focused Ion Beam (FIB) sculpting method. Two different configuration have been realized: a vertical configuration where the nanosensor loop is perpendicular to the substrate plane and a planar one having the SQUID loop parallel to the substrate plane. In both configurations the flux capture and the junction areas are 0.2 and 0.09 μm2, respectively. At liquid helium temperature the nanosensor have shown non-hysteretic current-voltage characteristics and large voltage modulation depths as well as high voltage responsivities. A spectral density of magnetic flux noise as low as 700 nΦ0/Hz1/2 has been measured in small signal mode using a low noise direct coupling electronics. The computed spin sensitivity has provided a value less than 10 Bohr magneton per bandwidth unit.