In a system of thin alternating layers of superconductors and insulators the equations describing static and dynamic fluxon solutions are derived. The approach, represented by a useful compact matrix form, is intended to describe systems fabricated for example of niobium or niobium‐nitride thin films; in the limit of ultrathin superconductor films it may give a model for describing fluxon motion in layered high‐T_c superconductors. Numerical examples of current versus voltage curves to be expected in such an experiment are presented.

We have investigated Josephson effects in stacks of both artificial and natural Josephson junctions. The measurements have been performed on Nb/Al-${\mathrm{AlO}}_{\mathit{x}}$/Nb multilayers and on small single crystals of ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_8$. Both systems exhibit multiple branched I-V characteristics in zero magnetic field. In finite magnetic fields coupling via currents flowing along the superconducting layers is essential, since the layers are thinner than the London penetration depth. All observations are in good agreement with numerical simulations of stacks of coupled Josephson junctions. These simulations predict that a large number of junctions can be phase locked in large magnetic fields via Fiske resonances excited in all junctions.

A ferroelectric memory field-effect transistor (FET) with a Pt-SrBi/sub 2/Ta/sub 2/O/sub 9/-Hf-Al-O-Si gate stack was fabricated and its electrical properties were characterized. The insulating and ferroelectric layers were successively deposited by a laser ablation technique. Excellent data retention characteristics were obtained. The drain currents of on- and off-states were measured as a function of time, after /spl plusmn/6 V poling voltage applied to the gate electrode. The current ratio of the on- and off-states was more than 10/sup 6/ even after 12 days. Moreover, after 10/sup 12/ cycles of /spl plusmn/8 V pulses, this ratio was also more than 10/sup 6/.

Thin films of multiferroic (Bi0.6Tb0.3La0.1)FeO3 were grown on Pt∕Ti∕SiO2∕Si substrate under various oxygen pressures by pulsed laser deposition technique. X-ray diffraction patterns show that the crystallinity of the thin film is improved with decreasing depositing oxygen pressure and the thin film grown at a lower oxygen pressure of 0.01torr exhibits a single perovskite phase with preferred (001) orientation. Leakage current of the as-deposited thin films decreases with decreasing grown oxygen pressure. Significantly, the leakage current of the thin films can be reduced largely by an annealing process at 800°C with flowing oxygen. The annealed thin films show a relatively high resistivity and stable polarization loops with double remnant polarization of about 3μC∕cm2. The conduction properties of the thin films have been well analyzed, and it is indicated that the dominant conduction mechanism is the space-charge-limited conduction for the thin film grown at higher oxygen pressure and the Poole-Frenkel conduction for the thin films grown at lower oxygen pressure.

Characteristic velocities of the electromagnetic waves propagating in vertically stacked Josephson transmission are theoretically discussed. An equation for solving n velocities of the waves in an n Josephson-junction stack is derived. The solutions of two- and threefold stacks are especially focused on. Furthermore, under the assumption that all parameters of the layers are equal, analytic solutions for a generic N-fold stack are presented. The velocities of the waves in two- and three-junction stacks by Nb-Al-${\mathrm{AlO}}_{\mathit{x}}$-Nb systems are experimentally obtained by measuring the cavity resonance (Fiske step) modes. Comparison of the theory with the experimental data reveals good quantitative agreement.

Self-aligned-gate Pt/SrBi₂Ta₂O₉/HfAlO/Si metal/ferroelectric/insulator/semiconductor (MFIS) field-effect transistors (FETs) were fabricated. Drain current (I _d) versus gate voltage curves of the MFIS FETs showed almost the same steepness as that of a non-self-aligned-gate Pt/HfAlO/Si metal/insulator/semiconductor FET. Long retention times with large on- and off-state I _d ratios were obtained for the MFIS FETs. The retention times more than 33 days with an on- and off-state I _d ratio over 10⁵ were demonstrated for the self-aligned-gate MFIS FET with a 2-µm-long and 80-µm-wide gate. This device showed the longest memory retention among all of the ferroelectric-gate FETs reported ever before.