YBA2CU3O7 STEP-EDGE DC SQUID WITH COPLANAR CONTROL LINES

A dc superconducting quantum interference device (SQUID) with coplanar control lines has been fabricated from a single layer of YBa2CU3O7 thin film. Step-edge junctions were formed using resist/Si double-mask layers. Current-voltage characteristics of this SQUID at 77 K show Shapiro steps under microwave irradiation and are qualitatively consistent with the resistively shunted junction (RSJ) model. The spacing between the closed loop and the coplanar control lines in the tested SQUIDs ranged from 0.2 to 1.5 mu m. The measured output voltage-control current characteristics showed that the experimentally derived mutual inductances were a function of the spacing, in agreement with the calculated results. The typical mutual inductance for a spacing of 1.0 mu m was similar to 0.5 pH, which is adequate for detecting signals of flux-transfer logic gates in which the typical logic amplitude is similar to 0.1 mA. A coplanar structure is thus useful for logic gate applications. (C) 1995 American Institute of Physics.