Superconducting-semiconducting hybrid memories are disclosed. These superconducting-semiconducting hybrid memories utilize semiconductor circuits to store information, and either superconducting or semiconducting or combinations of superconducting and semiconducting circuits, with at least some superconducting circuitry used, to write and read information. The state of memory cells in the hybrid memories is determined by utilizing superconductor current sensing schemes to detect currents in the bit-line, thereby avoiding any bit-line charging delays and other problems associated with purely semiconductor memories. Additional features of the superconducting-semiconducting hybrid memories include wide margins, dense packing of memory cells, low power dissipation and fast access times. Interface curcuitry for converting superconducting signals to signals compatible with semiconductor circuits and for converting semiconductor signals to signals compatible with superconducting circuits is also disclosed.

Superconductor-semiconductor hybrid memory circuits with superconducting three-terminal switching devices

The construction of microelectronic circuits from high‐transition‐temperature (Tc) superconductors requires techniques for producing thin‐film wires, insulating crossovers, and vias (window contacts) between wires. Together, these three components form a superconducting interconnect technology. The challenges encountered in developing such a technology for high‐Tc superconductors involve factors associated with the materials, the circuits and the fabrication techniques. The use of pulsed laser deposition in conjunction with shadow mask patterning, photolithographic pattern definition, acid etching, ion‐beam etching, and surface cleaning to produce multilayer interconnects from YBa2Cu3O7−x (YBCO) is discussed. These processes have been used to construct a variety of passive high‐temperature superconducting components and circuits, including crossovers, window contacts, multiturn coils, and flux transformers. Integrated magnetometers incorporating superconducting quantum interference devices, multichip modules with semiconductor die bonded to YBCO interconnect structures, and analog‐to‐digital converters have also been successfully demonstrated.

Thin‐film multilayer interconnect technology for YBa2Cu3O7−x

We review the synthesis methods and properties of single crystal, powder, and thin film TlBaCaCuO high-temperature superconducting (Tl-HTS) materials. With transition temperatures ≥ 100 K for several compounds, Tl-HTS materials present real opportunities for applications above 77 K. Experiments using (1) single crystals: determined precise structural parameters and identified the complex Tl1+–Tl3+ equilibrium model; (2) powders: studied the complex thermodynamic phase diagram; and (3) epitaxial films: studied fundamental properties such as electron pair symmetry and the effect of controlled extrinsic defects on flux pinning strength, as well as providing the large-area surfaces required for device applications.

Synthesis and properties of tl-ba-ca-cu-o superconductors

A three-terminal high-frequency active device made of a single film of a high T/sub c/ superconductor that is based on the magnetic control of flux flow is presented. The device is composed of parallel weak links with a nearby magnetic control line. A model has been developed that is based on solving the equation of motion of Abrikosov vortices subject to Lorentz viscous and pinning forces, as well as magnetic surface barriers. The model has been used to predict device transit time (computed from flux velocity) and device I-V curves. The predictions are compared to measured parameters with resulting very good agreement. >

A model and equivalent circuit for a superconducting flux flow transistor

Josephson flux‐flow transistors were made from long YBa2Cu3O7−δ bicrystal grain boundary junctions. A normal metal loop, separated from the junction by an SiO layer, was used as the current control line. The line modulated the critical current, Ic , which for temperatures ≤60 K showed the typical dependence for a long junction, while at higher temperatures the regular small junction modulation was seen. Current gain larger than unity was obtained below 70 K. The current gain increased with the junction length, and varied roughly like √Ic when decreasing the temperature. A transresistance larger than 5 Ω was obtained at 15 K. Better performance is expected from junctions with higher current densities.

Flux‐flow transistors based on long YBa2Cu3O7−δ bicrystal grain boundary junctions

A Tl-Ca-Ba-Cu-O superconducting flux flow transistor (SFFT) was used as an active impedance converter between Josephson and FET circuitry. The input of the flux flow device is a control line of low impedance that can be driven by a tunnel junction. The output is the signal across the SFFT which is made of a parallel array of weak links. The output impedance is typically greater than 5 Omega , with a maximum voltage swing of over 100 mV into a 50- Omega system. The switching of an all-Nb junction induced a 90-mV voltage swing at the FET input and over 200 mV at the FET output. The line driver can operate anywhere between 4.2 K and 85 K with minor changes in speed (+or-5 ps) and output level (+or-10 mV). The switching time measured was about 100 ps and was fixture limited.

J. S. Martens

Papers

A Josephson junction to FET high speed line driver made of TlCaBaCuO