Fabrication of Al/AlO_x/Al junctions using pre-exposure technique at 30-keV e-beam voltage

We fabricate high-quality A1/A1O_x/A1 junctions using improved bridge and bridge-free techniques at 30-keV e-beam voltage,in which the length of undercut and the size of junction can be well controlled by the pre-exposure technique.The dose window is 5 times as large as that used in the usual Dolan bridge technique,making this technique much more robust.Similar results,comparable with those achieved using a 100-keV e-beam writer,are obtained,which indicate that the 30-keV e-beam writer could be an economic choice for the superconducting qubit fabrication.     

利用倾斜角度蒸发法制备Al/Al_2O_3/Al超导隧道结

利用电子束曝光法对双层光刻胶进行曝光来制备悬空掩模结构,在此基础上利用电子束蒸发系统采用倾斜角度蒸发法制备铝超导薄膜,采用热氧化法在底层铝膜表面形成氧化铝作为势垒层,制备出铝SIS超导隧道结,并在360mK的情况下对铝结进行了Ⅰ～Ⅴ特性的初步测量.铝隧道结的成功制备为下一步构建超导量子比特器件,研究其量子特性奠定了良好的基础.     

Test investigation on interfacial characteristics of Cr/Al nanofilms structure

The objective of this paper is to provide a systematic test for fabrication or evaluation of a bilayer film structure between Cr and Al in micro/nanoelectronic manufacturing. The Cr/Al bilayer film is fabricated by using the magnetron sputtering. To understand the basic mechanical properties of the Cr/Al bilayer films, the elastic modulus and the hardness of the sample are investigated by using a nanoindenter test. The test can show the changing trend of the Cr/Al sample structure. To investigate the integrating characteristics of the sample in progress, the effect of the thermal cycling loading and no-thermal cycling loading on the integrating force of the Cr/Al samples is tested by using nanoscratch. The interfacial binding force in the films can be obtained for understanding the integrating characteristics. It builds a basis for future work on progress investigation of physical property of Cr/Al bilayer film structure.     

利用LiF/Al作为电极的有机电致发光器件

本文报道了利用LiF/Al作为负电极的有机电致发光器件,器件结构为ITO/TPD/Alq3/LiF/Al,LiF层的加入增强了电子注入,当其厚度为0.4nm时,器件的性能最好,与单层Al和Mg/Al电极的同类器件相比,此时器件的开启电压由Al电极时的4.3V和Mg/Al电极时的3.0V降低到了2.0V,器件的最大亮度分别由4000cd/m²、14000cd/m²提高到19600cd/m²,器件的发光效率也分别增加了5倍和2倍,达到2.66lm/W.     

Nanoporous Al sandwich foils using size effect of Al layer thickness during Cu/Al/Cu laminate rolling

The roll bonding technique is one of the most widely used methods to produce metal laminate sheets. Such sheets offer interesting research opportunities for both scientists and engineers. In this paper, we report on an experimental investigation of the ‘thickness effect’ during laminate rolling for the first time. Using a four-high multifunction rolling mill, Cu/Al/Cu laminate sheets were fabricated with a range of thicknesses (16, 40, 70 and 130 μm) of the Al layer. The thickness of the Cu sheets was a constant 300 μm. After rolling, TEM images show good bonding quality between the Cu and Al layers. However, there are many nanoscale pores in the Al layer. The fraction of nanoscale pores in the Al layer increases with a reduction in the Al layer thickness. The finite element method was used to simulate the Cu/Al/Cu rolling process. The simulation results reveal the effect of the Al layer thickness on the deformation characteristics of the Cu/Al/Cu laminate. Finally, we propose that the size effect of the Al layer thickness during Cu/Al/Cu laminate rolling may offer a method to fabricate ‘nanoporous’ Al sandwich laminate foils. Such foils can be used in electromagnetic shielding of electrical devices and noisy shielding of building.     

Fabrication and performance characterization of Al/Ni multilayer energetic films

Al/Ni multilayer bridge films, which were composed of alternate Al and Ni layers with bilayer thicknesses of 50, 100 and 200 nm, were prepared by RF magnetron sputtering. In each bilayer, the thickness ratio of Al to Ni was maintained at 3:2 to obtain an overall 1:1 atomic composition. The total thickness of Al/Ni multilayer films was 2 μm. XRD measurements show that the compound of AlNi is the final product of the exothermic reactions. DSC curves show that the values of heat release in Al/Ni multilayer films with bilayer thicknesses of 50, 100 and 200 nm are 389.43, 396.69 and 409.92 J?g^?1, respectively. The temperatures of Al/Ni multilayer films were obviously higher than those of Al bridge film and Ni bridge film. Al/Ni multilayer films with modulation of 50 nm had the highest electrical explosion temperature of 7000 K. The exothermic reaction in Al/Ni multilayer films leads to a more intense electric explosion. Al/Ni multilayer bridge films with modulation period of 50 nm explode more rapidly and intensely than other bridge films because decreasing the bilayer thickness results in an increased reaction velocity.     

磁性隧道结Ni80Fe20/Al2O3/Co的制备和物性

用等离子体氧化形成绝缘层的方法,重复性地制备出了Ｎｉ８０Ｆｅ２０／Ａｌ２Ｏ３／Ｃｏ磁性隧道结。样品的隧道磁电阻（ＴＭＲ）比值在室温下最高可达６．０％,翻转场（ｓｗｉｔｃｈ ｆｉｅｌｄ）可低于８００Ａ／ｍ,平台宽度约２４００Ａ／ｍ。结电阻的变化范围从几百欧姆到几百千欧。     

The effects of the ageing on the characteristic parameters of polyaniline/p-type Si/Al structure

A detailed study of the effects of the ageing on the characteristic parameters of polyaniline/p-type Si/Al structure has been presented. The polyaniline film has been formed on a p-type Si substrate by means of an anodization process. The polyaniline/p-Si/Al structure has demonstrated clearly rectifying behavior by the current–voltage (I–V) curves studied at room temperature. The current–voltage curves of the structure have been measured immediately, 15, 30, 60, 90 and 120 days after fabrication of the polyaniline/p-Si/Al structure. It has been seen that the characteristic parameters, such as barrier height (BH), ideality factor and series resistance of polyaniline/p-type Si/Al structure have slowly changed with increasing ageing time. The diode shows non-ideal I–V behavior with an ideality factor greater than unity that can be ascribed to the interfacial layer, the interface states and the series resistance.     

Fabrication and characterization of Al nanomechanical resonators for coupling to nanoelectronic devices

We report on a suspension technique for Al doubly clamped beams. The technique is based on two consecutive reactive ion etching processes in CF₄ plasma, anisotropic and isotropic, of SiO _x on which Al layer is deposited. With this technique, Al doubly clamped beams were fabricated. One of the beams was characterized using a magnetomotive measurement scheme at low temperatures. The developed suspension technique is suitable for the fabrication of Al nanoelectronic devices with a mechanical degree of freedom, in particular, superconducting flux qubits with partly suspended loops.     

Al3+对Ge/Al-SiO2薄膜光致发光的影响

采用磁控溅射及后退火技术制备了不同组份和不同退火温度的Ge、Al共掺SiO₂薄膜。通过对样品的X射线光电子能谱(XPS)测试,确定了薄膜的成分和结构特征;同时还测试了样品的光致发光谱(PL谱),得到了峰值位于420 nm附近的紫光发射峰和峰值位于470 nm的蓝光发射峰。实验结果表明, Al的掺杂不仅可以显著地提高GeNOV中心和SiNOV中心的光发射效率,还可以促进GeNOV缺陷和SiNOV缺陷中心的形成,进而有利于薄膜的光致发光。     

Al/Cu阻抗匹配状态方程测试靶制备工艺研究

 采用轧制技术和真空扩散连接技术,成功实现了Al/Cu阻抗匹配状态方程测试靶的制备,通过原子力显微镜（AFM）、扫描电镜（SEM）、X射线衍射（XRD）、台阶仪等测试方法,对样品结构及表面质量进行分析。结果表明：通过轧制技术制备的金属薄膜表面质量较好,表面粗糙度小于25 nm;扩散连接铝铜薄膜界面结合良好,为连续连接,扩散界面控制在150 nm以内。     

Prerequisites for high-quality magnetic tunnel junctions: XPS and NMR study of Co/Al bilayers

Aluminum films with thicknesses ranging from 1 nm to 12 nm have been sputtered on 20 nm thick Co layers. The properties of the Co/Al bilayers were studied by X-ray photoemission spectroscopy (XPS) and spin-echo nuclear magnetic resonance (NMR). Both methods show independently that a 1 nm Al film covers the Co surface completely. XPS and NMR also showed that layers thicker than 1 nm Al are not oxidized completely in ambient air. Similarities to and deviations from niobium with Al overlayers (Nb/Al) are described. Prerequisites for the fabrication of tunneling magnetoresistance devices based on Co or NiFe ferromagnets and an aluminum oxide barrier are discussed. Received: 7 July 1999 / Accepted: 11 November 1999 / Published online: 8 March 2000     

Superconducting phase qubits with shadow-evaporated Josephson junctions

We develop a fabrication process for the superconducting phase qubits in which Josephson junctions for both the qubit and superconducting quantum interference device(SQUID) detector are prepared by shadow evaporation with a suspended bridge. Al junctions with areas as small as 0.05 μm~2 are fabricated for the qubit, in which the number of the decoherencecausing two-level systems(TLS) residing in the tunnel barrier and proportional to the junction area are greatly reduced. The measured energy spectrum shows no avoided crossing arising from coherent TLS in the experimentally reachable flux bias range of the phase qubit, which demonstrates the energy relaxation time T_1 and dephasing time T_φ on the order of 100 ns and 50 ns, respectively. We discuss several possible origins of decoherence from incoherent or weakly-coupled coherent TLS and further improvements of the qubit performance.     

Interfacial characteristics of Al/Al2O3/ZnO/n-GaAs MOS capacitor

The interfacial characteristics of Al/Al2O3/ZnO/n-GaAs metal-oxide-semiconductor (MOS) capacitor are investigated. The results measured by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) show that the presence of ZnO can effectively suppress the formations of oxides at the interface between the GaAs and gate dielectric and gain smooth interface. The ZnO-passivated GaAs MOS capacitor exhibits a very small hysteresis and frequency dispersion. Using the Terman method, the interface trap density is extracted from C-V curves. It is found that the ZnO layer can effectively improve the interface quality.     

Spray pyrolised Al/ZnO: Al heterojunction: Effect of Al on junction properties

Al/ZnO: Al heterojunction was fabricated by depositing ZnO: Al film on Al substrate by spray pyrolysis technique at 220 °C substrate temperature. XRD, SEM and EDAX techniques were used to study the properties of thin films. Heterojunction properties were studied by I–V and C–V measurements. The fabricated Al/ZnO: Al junctions were rectifying in character. The room temperature ideality factors of Al/ZnO: Al junctions are found to vary from 2.56 to 5.45. The reverse saturation currents are 5.21 × 10⁻⁹, 1.35 × 10⁻⁶, 1.99 × 10⁻⁶, 9.99 × 10⁻⁷ and 1.02 × 10⁻⁷ A for Al/ZnO: Al junctions. Junction forward current depends on doping concentrations and temperature, whereas reverse saturation current remains independent for Al concentration. The built-in-potential calculated from capacitance for Al/ZnO: Al junctions are 2.74, 2.60, 2.0, 2.50 and 2.43 V corresponding to 1, 2, 3, 4 and 5 mol% of Al. X-ray diffraction study confirmed that the films are polycrystalline, orientated in (0 0 2) plane. Scanning electron microscopy study confirmed circular ring patterns with inside ribbon type structure for Al doped ZnO films.     

Properties of superconducting Nb/Al/Nb/Al?AlOx?Al?AlOx?Al/Nb/Al/Nb tunnel junctions

Modified geometry (MG) devices, Nb/Al/Nb/Al−AlO_x−Al−AlO_x−Al/Nb/Al/Nb, have been fabricated and investigated in comparison with the basic geometry (BG) double-barrier Nb/Al−AlO_x−Al−AlO_x−Al/Nb devices. The enhancement of the critical temperature in the Al film is found to be weaker for the MG devices as compared with the BG devices at temperatures nearT=4.2 K but stronger at lowT. Indication of an enhancement of dc Josephson critical current density,j _c , at bias voltageV≠0 as compared withj _c (V=0) has been observed in the MG devices for the first time.     

Rapid initiation of reactions in Al/Ni multilayers with nanoscale layering

Research into nanoenergetic materials is enabling new capabilities for controlling exothermic reaction rates and energy output, as well as new methods for integrating these materials with conventional electronics fabrication techniques. Many reactions produce primarily heat, and in some cases it is desirable to increase the rate of heat release beyond what is typically observed. Here we investigate the Al-Ni intermetallic reaction, which normally propagates across films or foils at rates lower than 10 m/s. However, models and experiments indicate that local heating rates can be very high (10⁷ K/s), and uniform heating of such a multilayer film can lead to a rapid, thermally explosive type of reaction. With the hopes of using a device to transduce electrical energy to kinetic energy of a flyer plate in the timescale of 100's of nanoseconds, we have incorporated a Ni/Al nanolayer film that locally heats upon application of a large electrical current. We observed flyer plate velocities in the 2-6 km/s range, corresponding to 4-36 kJ/g in terms of specific kinetic energy. Several samples containing Ni/Al films with different bilayer thicknesses were tested, and many produced additional kinetic energy in the 1.1-2.3 kJ/g range, as would be expected from the Ni-Al intermetallic reaction. These results provide evidence that nanoscale Ni/Al layers reacted in the timescale necessary to contribute to device output.     

Ion irradiation induced Al-Ti interaction in nano-scaled Al/Ti multilayers

Interactions induced in Al/Ti multilayers by implantation of Ar ions at room temperature were investgated. Initial structures consisted of (Al/Ti) × 5 multilayers deposited by d.c. ion sputtering on Si(1 0 0) wafers, to a total thickness of ∼250 nm. They were irradiated with 200 keV Ar⁺ ions, to the fluences from 5 × 10¹⁵ to 4 × 10¹⁶ ions/cm². It was found that ion irradiation induced a progressed intermixing of the multilayer constituents and Al-Ti nanoalloying for the highest applied fluence. The resulting nanocrystalline structure had a graded composition with non-reacted or interdiffused Al and Ti, and γ-AlTi and AlTi₃ intermetallic phases. Most intense reactivity was observed around mid depth of the multilayers, where most energy was deposited by the impact ions. It is presumed that Al-Ti chemical reaction is triggered by thermal spikes and further enhanced by chemical driving forces. The applied processing can be interesting for fabrication of tightly bond multilayered structures with gradual changes of their composition and properties.     

Characterization of Al/Si junctions on Si(100) wafers with chemical vapor deposition-based sulfur passivation

Chemical vapor deposition-based sulfur passivation using hydrogen sulfide is carried out on both n-type and p-type Si(100) wafers. Al contacts are fabricated on sulfur-passivated Si(100) wafers and the resultant Schottky barriers are characterized with current–voltage (I–V), capacitance–voltage (C–V) and activation-energy methods. Al/S-passivated n-type Si(100) junctions exhibit ohmic behavior with a barrier height of <0.078 eV by the I–V method and significantly lower than 0.08 eV by the activation-energy method. For Al/S-passivated p-type Si(100) junctions, the barrier height is ~0.77 eV by I–V and activation-energy methods and 1.14 eV by the C–V method. The discrepancy between C–V and other methods is explained by image force-induced barrier lowering and edge-leakage current. The I–V behavior of an Al/S-passivated p-type Si(100) junction remains largely unchanged after 300 °C annealing in air. It is also discovered that heating the S-passivated Si(100) wafer before Al deposition significantly improves the thermal stability of an Al/S-passivated n-type Si(100) junction to 500 °C.     

Electrical behaviour of lateral Al/n-GaN/Al structures

The electrical behaviour of lateral Al/n-GaN/Al structures has been studied by current-voltage measurements between a large pad with an area of 22 mm² and small contacts with different areas in the range of 0.01-1 mm². The results indicated that near room temperature the current was limited by the GaN layer exhibiting linear I-V characteristics for large contacts around 1 mm², while it was contact limited for small contacts around 0.1 mm² and below. This indicates that the same metal contact can behave as ohmic or rectifying depending on the contact area and so on the ratio of contact resistance to the series resistance of the structure.Near liquid nitrogen temperature, the current through the lateral Al/n-GaN/Al structures was limited by space charges. The Al/n-GaN contacts exhibited a very low Schottky barrier height below or around 0.2 eV. A new possible mechanism responsible for the temperature dependence of the ideality factor is proposed.