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Superconducting tunnel junction upper electrode events were separated from other electrode events and observed using a SQUID amplifier.

An interface circuit for a Josephson-complementary metal oxide semiconductors (CMOS) hybrid digital system was constructed. The proposed interface circuit consists of a parallel-in-parallel-out circuit and built-in Josephson-MOS amplifiers. It can be used to facilitate broadband data communication between Josephson and CMOS digital systems, amplify small Josephson-output signals and synchronize signals between the two systems.

Research was conducted to fabricate high quality Nb-based superconducting tunnel junctions (STJs)with an aluminum-oxide insulation layer for X-ray detection. The degree of phonon insulation from the substrate was tested using STJs with Al2O3 buffer layers of different thickness. Results indicate that Al2O3 is a good material to reduce the phonon induced signal from a Si substrate. It should also be noted that a single Al2O3 layer combines the role of a phonon insulation layer with that of an etch-stop layer.

Research was conducted to examine the performance of a prototype system of a superconducting tunnel junction X-ray detector and a superconducting quantum interference device (SQUID) preamplifier assembled in a 3He cryostat. The problem with the SQUID operation was addressed by using a niobium superconducting magnetic shield and a doubled cryogenic permalloy shield. Results indicate the possibility of constructing a compact superconducting-tunnel-junction-based X-ray detection system with an on-site low noise SQUID preamplifier.

Research was conducted to examine the transmission properties of a solder-bump via structure or use a chip-to-substrate connector in multichip module applications. Experiments were carried out using the Finite-Difference Time-Domain method which is based on the explicit solution of Maxwell's equations. Results indicate how the shape of a Rapid Single Flux Quantum pulse is affected by passing a discontinuity in the interchip signal path.

A study was conducted on the conversion gain and noise in superconductor-insulator-superconductor mixers using Nb/MgO/NbN junctions at the submillimeter and millimeter wavelengths. The junctions exhibited a lowest receiver noise of 65 K with -6 dB conversion gain at 162 GHz. At 306 GHz, receiver noise was 230 K with -10 dB conversion gain. The junction has a 2 micrometer2 junction area and a 1.4 KA/cm2 Josephson critical current density.

Rapid single-flux-quantum technology-based dual-rail logic circuit elements were developed and simulated. The timing information of dual-rail data enable the proposed circuits to operate asynchronously. A new approach based on a fully asynchronous dual-rail multiplexer was also proposed for transferring data from a serial flow-clocked circuit to a parallel dual-rail circuit.

A room temperature approach for NbN-MgO-NbN junction development is proposed. The approach allows the fabrication of hybride mixer chips on quartz substrates. A second Nb target functions as a selective nitrogen pump for creating the appropriate plasma conditions for NbN film deposition. Critical temperatures exceeding 15 K and normal state resistivities from 100 to 130 microohm cm were observed in NbN films on quartz substrates with and without intermediate layers of Nb, Al, Al/SiO2 and Nb/SiO2.

Current-voltage characteristics of Nb/AlOx/Nb tunnel junctions with high critical densities are investigated. Results show that Josephson self-coupling causes steep currents steps at odd submultiples of the gap voltage, an indication of its importance in high-critical density tunnel junctions. The data are in good agreement with those formulated using a simple junction model based on Werthamer's equation.

A speedup method for enhancing the switching mechanism in the direct-coupled four-junction Josephson logic gate is presented. The method uses an inductor connected to the gate's input-output separation resistance to speed up the switching process. This arrangement transforms the junctions to a resistive state, thereby enhancing the gate's overdrive capability. A logic delay experiment has revealed that the proposed method is capable of increasing the gate's switching mechanism speed by as much as 40%.

A 16-kilobit Josephson random-access memory (RAM) based on the miniaturized variable threshold cell is presented. The cell consists of a selection and writing gate made of a 3-junction superconducting quantum interference device gate. It has an access time of 475 picosecond and a total power dissipation of 7.3 milliwatts per chip. Experimental simulations hagve shown that the gate speed of the proposed RAM is two times faster than that of the 1-kilobit RAM.