摘要:

A two‐dimensionally focusing, quasi‐optical antenna having one elliptical reflector and one parabolic reflector has been built for use with a tunable gyrotron in order to carry out millimeter‐wave scattering measurements on the TORTUS tokamak plasma at the University of Sydney. The advantages of this antenna are the following: (1) The elliptical reflector focuses the radiation beam in the toroidal direction, while the parabolic reflector focuses in the direction of major radius. This gives excellent two‐dimensional focusing in the plasma region, and consequently excellent spatial resolution. (2) The focal point can be easily swept along the direction of major radius in the whole plasma region, simply by changing the angle of the parabolic reflector by a small amount. These features have been demonstrated experimentally using the tunable gyrotron source, GYROTRON III, and in computations of the radiated fields.

ISSN:0021-8979    

DOI:10.1063/1.345058

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effect of different passivation processes, i.e., anodic oxidation and/or photochemical deposition of SiO2on the current‐voltage characteristics of the InSbp+ndiodes was studied. By applying different voltages on the gate electrode over thep+njunction periphery, various kinds of current‐voltage characteristics can be induced, including multiple negative differential resistance in forward bias. This strongly indicates that the major part of the current, especially the reverse leakage current, flows through the surface of thep+njunction. Tunneling due to field emission from the valence band of thep+layer into a field‐induced inversion layer at the InSb/oxide interface in which the energy levels are quantized is responsible for the multiple negative differential resistance. Reverse leakage current as low as 20 &mgr;A/cm2at −1.1 V for ap+ntype diode withn‐type doping concentration of 2×1015cm−3could be easily achieved by applying a gate voltage of −9 V. It is also found that diodes with similar performance can be fabricated by properly adjusting the photochemical vapor deposition passivation process.

ISSN:0021-8979    

DOI:10.1063/1.345059

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A small‐signal theory of a field‐emission‐array distributed amplifier consisting of two microstriplike transmission lines is developed to calculate the premodulation in the input channel and the gain in the output channel. A first‐order perturbation analysis is used to treat the beam‐wave coupling in this device within the framework of a cold fluid model. The dependence of the linear gain on frequency, beam voltage, beam current, and the circuit parameters is derived to determine the parameter range for operation of the device. It is found that the height of the circuit is restricted to lie between 80 and 120 &mgr;m to maintain high electronic gain and low loss arising from the finite conductivity of the metal surfaces. In an output line having a substrate with a relative dielectric constant, &egr;r=4, a net gain of 7 dB/cm is calculated with a beam voltage of 60 V and a beam current of 2.14 A/cm in each wedge of a seven‐wedge emitter array. As the beam voltage is increased in the range 60–100 V, the net gain decreases from 7.0 to 3.0 dB/cm, while the frequency for maximum gain increases from 50 to 80 GHz with a corresponding increase in the bandwidth. The small‐signal instantaneous bandwidth is in excess of 60%.

ISSN:0021-8979    

DOI:10.1063/1.345060

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Experiments have been performed in which an explosively formed fuse transferred a fraction of the 10 MA output current from an explosively powered magnetic flux compression generator to a conventional exploding metallic fuse load. System malfunctions significantly reduced the current delivered to the load and changed the fuse performance. The resultant slowing of the fuse material’s trajectory through density‐temperature space allowed a correlation between optical and electrical diagnostics which indicated a significant delay between the onset of hydrodynamic motion and the onset of rapid resistance increase. The experiments have confirmed a computational model of the fuse load hydrodynamic behavior.

ISSN:0021-8979    

DOI:10.1063/1.345061

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The discharge behavior of silicon‐oxide‐nitride‐oxide‐semiconductor nonvolatile memory transistors is investigated for a range of programming and storage temperatures spanning −55 °C to 200 °C. A number of empirical observations strongly limit the nature of the mechanisms that govern charge injection and decay. Both electrons and holes contribute to the charge storage properties of the transistors, and the decay properties of both are thermally activated with a continuous distribution of activation energies (trap depths). Charge decay, for both charge states, is negligibly limited by mechanisms other than those which are strongly thermally activated. The programming temperature, relative to the storage temperature, significantly impacts the retention time of the excess electron state, while not affecting the long term decay of the excess hole state. The experimental results also have significant implications regarding proper retention screening techniques and nonvolatile ROM programming techniques.

ISSN:0021-8979    

DOI:10.1063/1.345062

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

High current densities in the collector layer reduce the cutoff frequency of heterojunction bipolar transistors. We develop a model based on analytical expressions that describe this reduction. These expressions represent the contributions from each of six regions defined in the output current‐voltage characteristic. The model has parameters determined entirely by device physical makeup. It has no fitting parameters. Its predictions agree well with experimental data taken on twoN/p+/naluminum‐gallium‐arsenide/gallium‐arsenide transistors having abrupt junctions grown by molecular‐beam epitaxy. Because previous models omitted the effects of high current densities, their predictions agree less favorably. The development of the model considers the effects that compound‐semiconductor properties such as velocity overshoot have on the cutoff frequency.

ISSN:0021-8979    

DOI:10.1063/1.344536

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

This paper deals with the instabilities of the metal‐oxide‐semiconductor (MOS) transistors with nitrided oxides as gate insulators. In order to relate, and to trade off among, the instabilities, the noise behaviors, and other electrical characteristics in these devices, extensive investigations on the electrical properties—including the flatband‐voltage shift, fixed‐oxide charge, interface‐state density, surface mobility, transconductance, and the electronic conduction in the insulating layer—were conducted with various amounts of hot‐electron injections. From the noise‐temperature and the interface‐state density measurements, we found that the electronic trap density at the nitrided‐oxide/silicon interface is significantly enhanced at around an energy level of 0.43 eV below the conduction‐band edge of silicon. On the other hand, results also suggest that the nitridation of the gate insulator in a MOS transistor can improve the stabilities again by hot‐electron bombardment, but suppresses the electron conduction in the inversion layer and enlarges the noise level remarkably under normal operation conditions. In addition, the degradation of the electrical characteristics of MOS transistors subjected to hot‐electron stressing seems to be due to the interface‐state generation rather than electron trapping.

ISSN:0021-8979    

DOI:10.1063/1.346060

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We report the results for the electronic structure of the interstitial Pd‐substitutional B complex in silicon. The self‐consistent field calculations were performed within the framework of scattered‐waveX&agr; cluster method. Compared with the electronic structures of the isolated substitutional B in silicon and of the isolated interstitial Pd in silicon, we found that the shallow acceptor B impurity state is deepened by the perturbation from the Pd atom. The ionic model, which is currently accepted to describe interstitial 3dtransition metal‐III A group shallow acceptor impurity pair, is not quite suitable to deal with the system of Pd‐B complex in silicon.

ISSN:0021-8979    

DOI:10.1063/1.344537

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

A solution of Br in absolute ethanol, previously shown to be effective at removing nonsuperconducting species from Y‐Ba‐Cu‐O thin film surfaces, is shown to also be effective in treating Bi‐Sr‐Ca‐Cu‐O thin film surfaces. X‐ray photoelectron spectra obtained after etching are consistent with previously reported results obtained from samples cleaved or scraped in vacuum.

ISSN:0021-8979    

DOI:10.1063/1.344538

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have used a scanning tunneling microscope to locally modify thin oxide films on silicon. Current‐voltage (I‐V) measurements were performed on these samples and compared with those on ‘‘as‐polished’’ (mechanically and chemically polished by the manufacturer). We found that theI‐Vmeasurements on samples with thin oxide films were nearly symmetric, characteristic of metal‐oxide‐semiconductor structures dominated by interface states. In contrast, we observed band‐bending on the ‘‘as‐polished’’ samples. The thin oxide film directly under the tip was modified by application of a voltage pulse. This change was reflected in theI‐Vmeasurements.

ISSN:0021-8979    

DOI:10.1063/1.344539

出版商:AIP    

年代:1990

数据来源: AIP