I.I. Vengrus

Magnetic field maps of YBCO thin films obtained by scanning SQUID microscopy for HTSC microelectronics

Scanning SQUID microscopy has been extended to record current-induced magnetic field maps of superconductor topologies based on YBCO film structures. The technique described can be used as a powerful tool for the diagnostics of superconductor integrated circuits and highly sensitive bolometers. This kind of diagnostics predicts the degree of integration which can be achieved at the modern level of HTSC microelectronics technology. One would expect an overall yield of 100-element chips at a level of in the production of superconducting YBCO/MgO bolometers.

A dc SQUID-based magnetic microscope study of the magnetic properties of the Ni thin films

We have applied a developed HTS dc SQUID based magnetic microscope for study of the magnetic properties of ultrathin Ni films. A magnetic moment sensitivity close to 10/sup -15/ A.m/sup 2//Hz/sup 1/2/ has been obtained at 77 K. The space resolution was determined at level of 100 /spl mu/m by the separation between the SQUID and the studied film surface. One-domain structure, in-plane orientation of magnetic moment and ferromagnetic-like ordering in 26 /spl Aring/ thick film were found. An absolute value of the film magnetic moment has been estimated.

YBCO THIN-FILMS SQUIDS FABRICATED ON BICRYSTAL SUBSTRATES

Properties of the dc SQUIDs made of YBCO thin film deposited on SrTiO3 and ZrO2 bicrystal substrates and the properties of the fabricated Josephson junctions have been studied. It is found that the characteristics of the junctions are similar to those of the SNS structures. The magnetic field sensitivity has achieved a value of δB ~ 10−12 T/Hz1/2 at frequencies higher than 25 Hz and T = 4.2 K.

Directly coupled electronics for HTSC DC SQUID based magnetometer

A low-volume high-performance directly coupled electronics for the high-T/sub c/ DC SQUID magnetometers has been developed and tested. This electronics is based on a liquid nitrogen cooled preamplifier with the white noise level close to 0.25 nV/Hz/sup 1/2/, packed in the volume less than 3 cm/sup 3/ and results in a typical 3 dB bandwidth of about 1 MHz, maximum dynamic range 140 dB for frequencies up to 1 kHz and the maximum slew rate more than 10/sup 6/ flux quanta in second with a middle-quality DC SQUID sensor.

Detection of the proximity effect in Au/YBCO bilayers at 77 K with the aid of a low-temperature scanning tunneling microscope

The characteristic features of the conductance of a tunneling contact, formed by a microscope tip and an Au/YBCO sandwich, are investigated with the aid of a scanning tunneling microscope. It is shown that there exist three types of dependences of the conductance of the structure on the applied voltage, which are distinguished by the position of the characteristic features on the voltage axis. It is established that this difference is due to the local characteristics of the proximity effect in gold films on a high-Tc superconductor surface. It is concluded that the transmittance of the YBCO/Au boundary is spatially strongly nonuniform.

Optical diagnostics for fabrication of YBCO thin film DC SQUIDs

Optical reflectance spectra of thin YBCO films on SrTiO/sub 3/ bicrystals were measured in a photon energy range of 1-3 eV at room temperature. Raman spectra measurements in the range 200-700 cm/sup -1/ were performed. The best samples were shown to have high reflectance anisotropy and a well-defined Raman peak /spl nu//sub 1/=500+1 cm/sup -1/. YBCO thin films on a bicrystal substrate that successfully passed optical control were used for Josephson junctions and DC SQUID fabrication. The fabricated SQUIDs operated at 77.3 K in the flux locked loop mode and had a typical white noise (1-2)/spl times/10/sup -5/ /spl Phi//sub 0//Hz/sup 1/2/ at frequencies higher than 200-500 Hz. The best magnetic field resolution was 650 fT/Hz/sup 1/2/ at frequencies f>200 Hz.<<ETX>>