MAGNETIC-FIELD SENSITIVITY OF VARIABLE THICKNESS MICROBRIDGES IN TBCCO, BSCCO, AND YBCO

We describe results of a study comparing the magnetic field sensitivit ies of variable thickness bridge (VTB) arrays fabricated in TBCCO, BSC CO, and YBCO thin films. Identical structures were patterned in a vari ety of films, and the bridges were thinned by four different methods. Analysis of the data yields experimental evidence as to the suitabilit y of these types of films for devices such as the superconducting flux flow transistor (SFFT) which is based on this geometry. The volt-ampe re characteristics of the arrays were measured in low uniform magnetic fields (less-than-or-equal-to 130 G) and in nonuniform fields (less-t han-or-equal-to 5 G) produced by a nearby control line. For these film s in this geometry, no measurable effect of the control line magnetic field was observed. Large values of transresistance and current gain c ould only be attained through a thermal mechanism when the control lin e was driven normal. Upper bounds for (magnetically generated) transre sistance (less-than-or-equal-to mOMEGA) and current gains (less-than-o r-equal-to 0.005) have been inferred from the uniform field data assum ing a standard best-case device geometry. All volt-ampere curves follo wed closely a power law relationship (V approximately I(n)), with expo nent n approximately 1.2-10. We suggest materials considerations that may yield improved device performance.