Proceedings of the First European Workshop on Low Temperature Electronics
J. Phys. IV France 04 (1994) C6-261-C6-266
Processing of DC SQUIDs for radiofrequency amplificationR. Chicault1, M.C. Cyrille1, Y. Berthier1, J.C. Villégier2, F. Pourtier2, H. Moriceau2 and S. Nicoletti3
1 Laboratoire de Spectrométrie Physique, BP. 87, 38402 Saint Martin d'Hères cedex, France
2 LETI, DOPT- Commissariat à l'énergie atomique, 17 rue des Martyrs, 38054 Grenoble cedex 9, France
3 CNR-Lamel, Via Gobetti, 101-40129 Bologna, Italy
The goal of this studies is to use dc Squids as low noise radiofrequency amplifier (Tn ≈1K) in the frequency range 1-150 Mhz and to integrate them in NMR probe. DC Squids have been built using planar technology and with two types of superconducting materials : low Tc(Nb) and High Tc(YBa2Cu3O7). Contrary to the traditional set up used in magnetometry (flux locked loop) the dc Squid is here fluxed biased near Φz=(2n+1)Φo/4 and no flux locked loop is connected. Small variations of flux (Φs<<Φo) introduced from signal source via the input coil are amplified following the transfer characteristic VΦ=dV/dΦ. The low Tc devices are set up to now the best, concerning the reproducibility and the qualities of the Josephson Junctions obtained with a three layer process Nb/Al-Al2O3/Nb. Such junctions have been realized following the so called SNOP process, without anodization. The main characteristic obtained at 4.2K are RJ/RN=10, 2Δ≈2.8 meV and a Josephson current density J≈103 A/cm2. The high Tc devices have been built with bi-epitaxial YBa2Cu3O7 junctions and with a 30x30µm2 area loop. I(V) and V(Φ) characteristics curves obtained are promizing for applications as RF detection in the temperature range : 4-77K. Modelization studies are currently in progress for the optimization of those devices (low Tc and high Tc) as RF amplifiers (minimization of parasitic capacitance between the input coil and the Squid loop) in order to increase their upper frequency limit. * This work is partially supported by Ultimatech (CNRS), by the "région Rhône-Alpes" and E.E.C. "HTSC-GBJ" programs n°7100.
© EDP Sciences 1994