Development of scanning SQUID microscope for studying superconducting films and devices

A micro-imaging system using a low-temperature superconductor (LTS) scanning SQUID microscope (SSM) has been developed for the study of superconducting films and devices. The system consists of a micro DC-SQUID, a cryostat, a precise scanning stage, and a control unit. The spatial resolution was improved by reducing the size of the pick-up coil of the micro DC-SQUID. A cryostat without liquid nitrogen makes the operation of the system easy and speedy. Preliminary experiments were made using the system and several magnetic images were obtained. We present observations of trapped fluxes in two types of superconducting thin film: a single-crystal-like Nb film grown epitaxially and a polycrystalline Nb film. We also present observations of a SQUID array, which consists of 50 DC-SQUIDs connected in series. (C) 2000 Elsevier Science B.V. All rights reserved.