  Superconducting quantum interference devices (SQUIDs) are used for
applications ranging from sensitive magnetometers to low-temperature
electronics and quantum computation. We introduce a planar nano SQUID that was
made with a single lithographic step out of NbN films as thin as 3 nm on a Si
chip. The fabrication process of weak links that are 45 nm in width, and 165 nm
in length, which were designed to account for overcoming current crowding are
presented. Operation at a temperature range of 20 mK to 5 K as well as at 1 T
parallel, and 10 mT perpendicular magnetic fields is demonstrated, while
potential operation higher than 8 T has also been shown. The broad range of
applicability of a single device as well as its scalability are promising for
on-chip integrability that may open new technological possibilities, including
in quantum and electro-optical circuiting.
