Direct growth of Josephson junctions and nanoSQUIDs using focused ion beam induced deposition

Focused ion beam induced deposition (FIBID) using the W(CO)₆ precursor allows the direct growth of superconducting nanostructures with very high lateral resolution and without the need of any resists. In the past, we have successfully grown superconducting W-C nanowires with 50 nm width using a Ga⁺-FIB and with 20 nm width using a He⁺-FIB. In the present contribution, we will show our current efforts to directly grow Josephson junctions and nanoSQUIDs by Ga⁺-FIBID  using the W(CO)₆ precursor. By combining two large rectangular patterns with two narrow nanowires, we successfully create Dayem-bridge-based nanoSQUIDs on flat SiO₂//Si substrates with dimensions 300 nm x 700 nm. From current-versus-voltage measurements under various applied magnetic fields, the expected periodic voltage response as a function of the penetrating magnetic flux is obtained, confirming that well-behaved Josephson junctions form at the nanowires and a SQUID response is achieved. Given the high resistance of W-C at the normal state, the SQUID transfer coefficient obtained is large, in the range of 1 mV/Φ₀ for a driving current around 8 μA. Interestingly, the same growth strategy of these nanoSQUIDs has been successfully implemented on cantilevers for future applications in advanced scanning probe microscopy.