High performance step-edge squids on a sapphire substrate and method of fabrication

摘要

YBCO step-edge junctions and SQUID on sapphire substrates using CeO2 as a buffer layer are fabricated. A steep step-edge is formed in the CeO2 buffer layer by the Ar<+> ion milling of the buffer layer over a shadow mask having an overhang end structure which allows for an extended time of milling for forming a deep steep step-edge within the buffer layer. The step angle is greater than 81 DEG as measured by AFM. A high quality YBCO film is then epitaxially grown by pulse laser deposition. After patterning, the junctions display RSJ-type I-V characteristics. The sapphire based YBCO step-edge SQUIDs are installed onto a SQUID microscope system. SQUIDs fabricated by the step-edge technique exhibit excellent magnetic field modulation, high imaging qualities, and low noise. <IMAGE>