摘要:

The fabrication and electrical performance of an all refractory, eight mask step, NbN medium scale integrated circuit process are discussed.Insiturf sputter deposited trilayers of NbN/MgO/NbN are plasma etched to fabricate Josephson junctions. A novel low temperature, plasma enhanced chemical vapor deposited SiO2film is used for wiring and resistor insulation. Sputter deposited molybdenum films are used for resistors. Tunnel junctions fabricated with this process haveVm=61 mV atjc=1100 A/cm2, andVg= 5.1–5.2 mV at 4.2 K. Critical currents are uniform to within ±3% for 101 junction strings and are within ±25% over all die on 3 in. wafers. This process has been used to fabricate 8‐bit single flux quantum counter circuits,squidmagnetometer circuits, 870 junction strings, and arrays of 256squids. Preliminary circuit testing indicates operation at temperatures within the range of small closed‐cycle refrigerators.

ISSN:0021-8979    

DOI:10.1063/1.346145

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We present a theoretical study of a recently proposed class of quantum interference transistors that utilize quantum interference effects in ultrasmall semiconductorTstructures. Our analysis reveals that the attractive features of these transistors are the very low power‐delay product and multifunctionality; whereas the major drawbacks are extreme sensitivity of the device characteristics to slight structural variations, low gain, and low extrinsic switching speed in digital circuits caused by a large resistance‐capacitance (RC) time constant arising from an inherently low current‐carrying capability. The low switching speed of the transistors can however be improved dramatically by switching the device optically rather than electronically, using virtual charge polarization caused by optical excitation. This mode of switching (which is possible because of the small value of the threshold voltage) eliminates theRCtime constant limitation on the switching time and results in an ultrafast optoelectronic switch.

ISSN:0021-8979    

DOI:10.1063/1.346146

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Superconducting YBa2Cu3O7films withTc=84 K were deposited on polished polycrystalline BeO substrate by reactive evaporation andinsituannealing in a low‐pressure oxygen atmosphere. By this process the surface quality of the films is the very same as the substrate. At low annealing temperature (TR=650 °C) the film is not textured but shows good superconducting properties. Thec‐axis orientation perpendicular to the plane of the substrate is observed forTR=780 °C.

ISSN:0021-8979    

DOI:10.1063/1.346147

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Using (100) Cu(1000 A˚) /Ni/Cu(1000 A˚) structures with a different Ni thickness, a complete reversal in magnetic anisotropy is observed between the structures with 1000 and 50 A˚ Ni, respectively. The structures were deposited on (100) Si, with the first Cu layer in the (100) orientation as the seed, followed by epitaxial Ni and another Cu layer. Comparing the magnetization for the field applied parallel to the film plane,M∥, with that perpendicular to it,M⊥,M⊥is found to increase andM∥, to decrease with decreasing Ni thickness. At a Ni thickness of 50 A˚, a squared hysteresis loop is observed forM⊥. TheM∥curve, on the other hand, changes from a normal one at 1000 A˚ Ni to one with little hysteresis at 50 A˚ Ni. These are accompanied by an increasing deformation of the (100)Ni cubic lattice into a tetragonal one with decreasing Ni thickness, due to its mismatch with Cu. The deformation is discussed to assess the roles of stress in the observed reversal in magnetic anisotropy.

ISSN:0021-8979    

DOI:10.1063/1.346127

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Optically transparent, free‐standing single crystals of the high‐temperature superconductor Bi2Sr2CaCu2O8have been prepared with a typical size ofa×b×c=1 mm×1 mm×1500 A˚. The thickness of the samples has been determined by x‐ray transmission measurements and was found to be uniform to within a lattice spacing. Transmission electron microscopy and diffraction revealed a pseudotetragonal lattice with a twinning free, incommensurate superstructure. X‐ray microanalysis shows that the composition of the sample is homogeneous. Electrical resistivity and magnetic susceptibility measurements indicate that the crystals are good quality superconductors.

ISSN:0021-8979    

DOI:10.1063/1.346118

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The emission spectra resulting from ion beam sputtering a Y‐Ba‐Cu‐O target were observed as a function of beam voltage and beam current. The spectra were relatively clean with several peaks readily attributed to each of Y, Ba, and Ar. Monitoring of copper and oxygen was more difficult with a single CuO peak and one O peak evident. The intensities of the cation peaks were linear with respect to beam voltage above 400 V. Since target current was found not to be directly proportional to beam current, target power was defined as the product of beam voltage and target current. The response of cation peak height to changes in target power was linear and similar for variations of either beam voltage or target current.

ISSN:0021-8979    

DOI:10.1063/1.346119

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Spatially resolved measurements of the change in resistance with temperature of bulk high‐temperature superconductors are generated by heating a localized region of a sample with a modulated laser beam. The amplitude of the thermally induced resistance change is related to the heat capacity and derivative of resistance with temperature whereas the phase of the signal is related to the thermal diffusivity of the sample. By moving the sample with respect to the focused laser beam, spatially resolved measurements may be made. Images with ∼50‐&mgr;m resolution have been used to locate defects in polycrystalline Bi‐Sr‐Ca‐Cu‐O sample and to estimate the thermal diffusivity of the bulk material.

ISSN:0021-8979    

DOI:10.1063/1.346120

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

We have measured the epitaxial growth rate of Si in the disilane/hydrogen system for different experimental conditions in a rapid thermal processing–low‐pressure chemical vapor deposition reactor. The measured activation energy is about 43 kcal/mol for temperatures below 700 °C. The growth rate dependence on disilane or hydrogen partial pressures is measured in order to verify the reliability of a proposed model for the decomposition of the disilane molecule in the torr pressure regime. The obtained crystal quality is comparable to that obtained with silane gas except for higher growth rate in the disilane system.

ISSN:0021-8979    

DOI:10.1063/1.346121

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

An efficient numerical algorithm was developed to solve the continuity equations describing charged particle transport and potential distribution in a low‐pressure glow discharge in an argonlike gas. A parametric investigation of the effect of gas pressure and electrode spacing on the discharge properties was conducted.

ISSN:0021-8979    

DOI:10.1063/1.346122

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Stable and highly reproducible current‐limiting characteristics are observed for polycrystalline ceramics prepared by sintering mixtures of coarse‐grained, donor‐doped BaTiO3(tetragonal) as the major phase and ultrafine, undoped cubic perovskite such as BaSnO3,BaZrO3, SrTiO3, or BaTiO3(cubic). The linear current‐voltage (I‐V) relation changes over to current limiting as the field strength increases, when thermal equilibrium is attained. The grain‐boundary layers with low donor and high Sn, Zr, or Sr have depleted charge carrier density as compared to that in the grain bulk. The voltage drop at the grain‐boundary layers diminishes the temperature gradient between the interior and surface regions.

ISSN:0021-8979    

DOI:10.1063/1.347161

出版商:AIP    

年代:1990

数据来源: AIP