Fabrication of high quality Nb/AlOx-Al/Nb Josephsonjunctions. II. Deposition of thin Al layers on Nb films

The surface of thin Al layers deposited on Nb films with different sputtering parameters was studied. The anodization profile and X-ray photoelectron spectroscopy (XPS) confirmed that the underlying Nb layer is wet by a thin 2.9-nm Al layer, and the oxide formation on the Nb layer is completely suppressed. The excellent surface coverage is due to the affinity of Al for Nb and is quite different from the degraded coverage of Al on Si. It was observed that the surface coverage of Al on Nb depends on the film characteristics of the underlying Nb layers. Nb/AlO_x-Al/Nb junctions with lower Nb layers deposited with different sputtering parameters were fabricated. The authors verified that the quality of the junction is closely related to the surface coverage as analyzed by the anodization profiles and XPS     

Fabrication of high quality Nb/AlOx-Al/NbJosephson junctions. III. Annealing stability ofAlOx tunneling barriers

For pt.II see ibid., vol.2, p.84 (1992). Changes in current-voltage characteristics of Nb/AlO_x-Al/Nb Josephson junctions due to annealing are studied. The surface of the Nb counterelectrode was plasma-nitrided to clarify the effects of oxygen diffusing from it. From anodization profiles, it was confirmed that surface nitridation protects the tunneling barrier from oxygen diffusion. Surface nitridation improved the junction stability for long annealing. The decrease in critical current at initial annealing was found to be independent of nitridation. The annealing stability of AlN _x barrier junctions, compared to that of AlO_x barrier junctions, was measured, and it was concluded that the decrease at initial annealing is due to changes in the AlO_x barrier itself     

Production of high quality Nb/Al-oxide/Nb SIS trilayers for submillimeter wave mixers

Owing to a very sharp nonlinearity in the quasiparticle currentvoltage characteristic, which fortuitously occurs on the scale of a few millivolts rather than a few volts as with semiconductor devices, superconductor/insulator/superconductor (SIS) tunnel junctions are the most sensitive detectors for heterodyne mixing at millimeter and submillimeter wavelengths. They can also provide sources of coherent local oscillator power at very high frequencies; more broadly, they have a number of interesting applications as fast, low-power logic elements and as detectors at optical wavelengths. For submillimeterwave mixers, in many ways the most demanding of these applications, the Nb/Al-oxide/Nb material system has emerged as the system of choice to frequencies of ～ 700 GHz and beyond. Production of SIS devices requires careful attention to a number of critical microfabrication issues, and I describe here some of the insights gained from developing a process for high-quality niobium trilayers that successfully yielded small-area junctions with unusually low sub-gap leakage current.     

Fabrication of sub-micron Nb/Al-oxide/Nb sis junctions

I describe a process for fabricating high critical current density, submicron superconductor/insulator/superconductor (SIS) tunnel junctions, suitable for use as millimeter-wave or submillimeter-wave mixers. The superconducting electrodes are niobium; the insulating barrier is aluminum oxide. Standard optical photolithography is employed, with subsequent shrinkback of the photoresist mesa defining the device through reactive-ion etching in an oxygen plasma to enhance step-coverage by the insulating layer. Active areas as small as 0.5µm² have been made. I discuss two variations of the process, one starting from a small initial trilayer region defined by liftoff, and the other starting from a whole-wafer initial trilayer.     

Annealing properties of high quality Nb/Al-AlOx/Nbtunnel junctions

High quality, low current density Josephson tunnel junctions are obtained from Nb/Al-AlO_x/Nb trilayers, using a SNAP process to define the junction area. A large number of junctions has been annealed in air for several hours at temperatures as high as 300°C. The most relevant effects observed were: a) a marked decrease of the junction current density and a related increase of the normal-state resistance; b) under suitable conditions, a barrier quality improvement measured in terms of the subgap current and of the quality factor V_m; the most remarkable result is a V_m as large as 2.5 V at T=1.2 K for our best sample. We believe that oxygen diffusion through the Nb grain boundaries is the main mechanism responsible for the normal-state resistance increase and that device quality variation is closely related to the modification of the barrier interfaces     

A Cu-Al2O3-Al moisture sensor for high humidities

A novel humidity sensor using the structure Cu-Al₂O₃-Al has been developed for high humidity applications. The capacitance and conductance characteristics of the sensor, measured as a function of humidity at different frequencies, are given. The temporal drift in the characteristics is also investigated. A theory describing the operational behaviour of this device is proposed based on the humidity-sensitive spreading conductance of the oxidised copper film. This ingenious technique has a remarkable multiplicative action on the high humidity sensitivity.     

Fabrication and characterisation of high quality ZnO thin films by reactive electron beam evaporation technique

High quality zinc oxide thin films have been deposited on silicon substrates by reactive e-beam evaporation in an oxygen environment. The effect of the growth temperature and air annealing on the structural, optical and electrical properties has been investigated. X-ray diffraction measurements have shown that ZnO films are highly c-axis-oriented and that the linewidth of the (002) peak is sensitive to the variation of substrate temperature. The optimum growth temperature has been observed at 300 °C. Raman spectroscopy has been found to be an efficient tool to evaluate the residual stress in the as-grown ZnO films from the position of the E₂ (high) mode. On the other hand, the vanishing of the 574 cm⁻¹. Raman feature after annealing has been explained as due to an increase of grain size and the reduction of O-vacancy and Zn interstitial. The SEM images have shown that the surfaces of the electron beam evaporated ZnO became smoother for the growth temperatures higher than 300 °C. The optical transmittance is the highest at 300 °C and has been increased after annealing in air showing an improvement of the optical quality. Finally, the maximum electrical resistivity has been found at 300 °C, which explains its relation with the crystal quality and increased from 5.8×10⁻² Ω cm to reach an approximate value of 10⁹ Ω cm after annealing at 750 °C.     

Sputtered growth of high mobility InN thin films on different substrates using Cu-ZnO buffer layer

This work reports the growth of c-plane textured InN thin films on Cu-ZnO buffered silicon, c-sapphire, bulk GaN and quartz substrates. A Cu-ZnO buffer layer was deposited on all the substrates before the growth of InN film. A highly c textured film was obtained on sapphire and quartz substrates. Structural properties were calculated using XRD and Raman analysis. It was observed that, induction of Cu-ZnO buffer layer reduced the lattice mismatch between Si/GaN substrates and InN film. The bandgap of the films was obtained using UV visible reflectance spectroscopy. Hall measurements show high mobility films in the range of 119–223 cm²/Vs and an electron concentration of 10¹⁹. These results are in good agreement with previous results but are first time recorded using RF magnetron sputtering. Surface topography of the films showed smooth surfaces, which are due to reduced lattice mismatch between film and the substrate.     

高光束质量弹载激光主动成像激光器研制

弹载激光主动成像制导技术是现代战争中最重要的精确制导技术之一。其中,弹载激光主动成像激光器的研制,是当前研究的热点和难点。报道了高光束质量弹载1 064 nm激光器,用于激光主动成像。采用二极管端面带内泵浦Nd:YAG晶体,光机电一体化设计,在重复频率100 Hz时,输出激光脉冲宽度为3.005 ns,最大输出单脉冲能量3.36 mJ,输出激光光谱宽度78 pm。带内泵浦和谐振腔的优化设计,保证了良好的光束质量,光束质量因子M2在X方向为1.327,Y方向为1.354。成像结果表明:该激光器的成功研制,对高光束质量一体化固体激光器的参数设计和弹载激光器在激光主动成像中的工程应用都具有一定的指导意义。     

Fabrication of CNTs/Cu composite thin films for interconnects application

Carbon nanotubes/copper (CNTs/Cu) composite thin films were fabricated by combined electrophoresis and electroplating techniques. Electrical properties and structure of both CNTs/Cu thin films and the reference pure Cu thin films were investigated after annealing at different temperatures. The sheet electrical resistance of CNTs/Cu films decreases faster than that of pure Cu films with increase of annealing temperature. The grain size of CNTs/Cu film becomes much larger than that of pure Cu film at the same annealing temperature. The peak relative intensity of Cu (1 1 1) plane in CNTs/Cu film was stronger than that of pure Cu film. CNTs/Cu composite thin films, with better electrical properties than that of conventional pure Cu thin films, have been fabricated by electrophoresis and electroplating deposition techniques.     

Chlorobenzene vapor assistant annealing method for fabricating high quality perovskite films

In this study, chlorobenzene (CB) vapor assistant annealing (VAA) method is employed to make high quality perovskite films and produce high efficiency CH₃NH₃PbI_3-xCl_x perovskite solar cells. The perovskite films made by this method present several advantages such as increased crystallinity, large grain size and reduced crystal boundaries compared with those prepared by thermal annealing (TA) method, which is beneficial to charge dissociation and transport in hybrid photovoltaic device. In addition, it is found that the CB VAA method could improve the surface property of perovskite film, resulting in a preferable coverage of PCBM layer and a better interfacial contact between perovskite film and upper PCBM film. Consequently, the short circuit current density (J_sc) of the devices is significantly increased, yielding a high efficiency of 14.79% and an average efficiency of 13.40%, which is 13% higher than that of thermal annealed ones. This work not only put forward a simple and efficient approach to prepare highly efficient perovskite solar cells but also provide a new idea to improve the morphology and interfacial contact in one integration step.     

Fabrication of Au/PEDOT stacked electrodes for organic thin film transistors by imprinting technology

In this work, the Au/PEDOT stacked source/drain electrodes of OTFTs were fabricated by combining the micro-contact inking and reversal imprinting. The PEDOT was inked on the mold by the micro-contact process and the Au/PEDOT stacked layer was transferred on pentacene by imprinting technology. The threshold voltage, and on-off ratio, carrier mobility, and source/drain contact resistance of organic TFTs were all improved by the proposed process.     

Fabrication and adhesion strength of Cu/Ni-Cr/polyimide films for flexible printed circuits

The adhesion strength of a Cu/Ni-Cr/polyimide flexible copper clad laminate (FCCL), was evaluated according to the thickness of the Ni-Cr (Ni:Cr = 95:5 ratio) seed layer using the 90° peel test. The changes in the morphology, chemical bonding and adhesion properties were characterized by SEM, AFM and XPS. The peel strength of the FCCL increased with increasing thickness of the Ni-Cr seed layer, due to the increase in the ion bombardment caused by the higher power used in the Ni-Cr sputtering process. This increase in the FCCL peel strength was attributed to the lower proportion of C-N bonds and higher proportion of C-O bonds in the polyimide surface. The adhesion strength between the metal and polyimide was mostly attributed to the chemical interaction between the metal layer and the functional groups of the polyimide.     

Fabrication of p-n junction GaAs solar cells by a novel method

p⁺-n diffused junction GaAs solar cells have been successfully fabricated using a novel method in which the diffusion source, anti-reflective coating and protective cover layer are all formed in a single chemical vapor deposition run. The advantage of this process lies in its simple, low cost fabrication procedure and in the fact that the GaAs surface is protected throughout the fabrication procedure.     

基于Nb/Mc口的话音质量评估研究

随着移动通信日益普及,用户对服务品质和性能的要求也越来越高。话音业务作为用户最基本的业务,是评价用户感知质量的最重要方面。如何客观评估话音质量,高效地发现现网话音业务中存在的问题,定位问题的产生原因,都是移动通信网络维护面临的新课题。本文研究的内容,就是通过分析现网的话音媒体流,对用户通话的质量进行评估,定位话音降质的故障原因及故障点,并使媒体流的分析能够结合实际工作的需要,提供与话音质量相关的核心网、无线网支撑服务,即研究网络改造解决新方案。     

氮化Si基ZnO/Ga_2O_3制备GaN薄膜

利用射频磁控溅射法在Si衬底上先溅射ZnO缓冲层,接着溅射Ga2O3薄膜,然后ZnO/Ga2O3膜在管式炉中常压下通氨气进行氮化,反应自组生成GaN薄膜。XRD测量结果表明,利用该方法制备的GaN薄膜是沿c轴方向择优生长的六角纤锌矿多晶结构的薄膜,利用SEM观测了其表面形貌,PL测量结果发现了位于351nm处的室温光致发光峰。     

高质量InSb薄膜的MBE同质和异质外延生长

InSb是3~5 μm中波红外波段具有重要研究意义的材料。本文以单位内部生产的InSb(100)衬底为基础,通过摸索InSb(100)衬底的脱氧、生长温度和V/III束流比,获得了高质量的InSb同质外延样品,1.5 μm样品的表面粗糙度RMS≈0.3 nm(10 μm×10 μm),FWHM≈7 arcsec;采用相同的生长温度和V/III束流比并采用原子层外延缓冲层的方法在GaAs(100)衬底上异质外延生长本征InSb层,获得了较高质量的异质外延InSb样品,1.5 μm样品的室温电子迁移率高达6.06×104cm2 V-1s-1,3 μm的样品最好的FWHM低至126 arcsec。InSb材料的同质和异质外延优化生长可为高温工作掺Al的InSb器件结构的优化生长提供重要参考依据。     

Magnetic designs and field quality of Nb/sub 3/Sn accelerator magnets

This paper presents a new approach to accelerator magnet design, based on simple and robust single-layer coils with minimum number of turns arranged horizontally or vertically in a common iron yoke. Cos-theta and block type coil geometries as well as cold and warm iron yoke designs were studied. Coils and yokes were optimized for the maximum field, minimum field harmonics, and minimum sizes.     

Utilization of coordinating green solvents for high quality methylammonium bismuth iodide thin films for photovoltaic applications

Photovoltaic performances of the bismuth-based solar cells are profoundly affected by the thin film quality of the photoactive layer. Herein, we report on various green solvent system to obtain the highly crystalline, pinhole free and homogeneously methylammonium bismuth iodide (MBI) active layer. The MBI structure prepared with tetrahydrofuran:2-ethoxy-ethanol (THF-2ETO) solvent system was found to have the best film quality. Adding 0.05 M 2ETO as the co-solvent is sufficient to produce high quality BiI₃ and MBI thin films. According to the X-ray photoelectron spectroscopy (XPS) analyzes, we have demonstrated that there is an interaction between BiI₃ and 2ETO according to the concentration of 2ETO added to the main THF. Our study clarifies the importance of THF-2ETO solvent system that can accelerate the evolution of the Bi-based solar cells by creating high-quality BiI₃ or MBI thin films.     

Fabrication and characterization of Zr-rich Zr-aluminate films for high-κ gate dielectric applications

Two kinds of Zr-rich Zr-aluminate films for high-κ gate dielectric applications with the nominal composition of (ZrO₂)_0.8(Al₂O₃)_0.2 and (ZrO₂)_0.9(Al₂O₃)_0.1, were deposited on n-type silicon wafer by pulsed laser deposition (PLD) technique at different deposition conditions. X-ray diffraction (XRD) reveals that the (ZrO₂)_0.8(Al₂O₃)_0.2 film could remain amorphous after being rapid thermal annealed (RTA) at the temperature above 800 °C, while the other one displays some crystalline peaks at 700 °C. The energy gap calculated from optical transmittance spectrum of (ZrO₂)_0.8(Al₂O₃)_0.2 film on quartz is about 6.0 eV. Sputtering depth profile of X-ray photoelectron spectroscopy and Auger electron spectroscopy indicate that a Zr-Si-O interfacial layer was formed at the near surface of the silicon substrate. The dielectric constant of the (ZrO₂)_0.8(Al₂ O₃)_0.2 film has been determined to be 22.1 by measuring a Pt/(ZrO₂)_0.8(Al₂ O₃)_0.2/Pt MIM structure. An EOT of 1.76 nm with a leakage current density of 51.5 mA/cm² at 1 V gate voltage for the film deposited in N₂ were obtained. Two different pre-treatments of Si substrates prior to depositions were also carried out and compared. The results indicate that a surface-nitrided Si substrate can lead to a lower leakage current density. The amorphous Zr-rich Zr-aluminate films fabricated by PLD have promising structure and dielectric properties required for a candidate material for high-κ gate dielectric applications.