Intermodulation measurements in YBaCuO films

A technique for measuring the intermodulation signal arising in a nonlinear high-temperature superconductor film is suggested. Using a one-port resonator, the technique significantly increases sensitivity of the measuring system as compared to that of a two-port-resonator design. Specifically, it lowers the minimum measurable power at a given magnetic field strength on the film surface. Measurements of the intermodulation signal power as a function of the input power for YBaCuO films differing in surface resistance and thickness are reported. Based on the measured data, the intermodulation characteristic magnetic field is computed. The quantity characterizes nonlinear film properties of the regardless of the measuring system employed.     

Structural and electrical properties of perovskite ruthenate-based lead-free thick film resistors on alumina and LTCC

CaRuO₃ perovskite-based lead-free thick-film resistors (TFRs) were prepared on 96%-alumina and Low Temperature Co-fired Ceramic (LTCC) substrates. The microstructure evolution, possible interactions, and electrical properties of resistors were investigated. The hot and cold TCR values of all the resistors were measured in the temperature range (+20 to +120 ^∘C) and (+20 to −120 ^∘C), respectively. TFRs with 25% by vol. of CaRuO₃ on alumina exhibit a sheet resistance R_s = 5kΩ/sq. with hot and cold TCR of 225 and 470 ppm/^∘C respectively, whereas the same composition gives 1.2 kΩ/sq., 16.5 kΩ/sq. and 0.7 kΩ/sq. for co-fired, post-fired resistors on LTCC and buried resistors, respectively. The hot (HTCR) and cold (CTCR) values were evaluated; HTCR = 190 ppm/^∘C and CTCR = 314 ppm/^∘C were found for co-fired structures; HTCR = 216 ppm/^∘C and CTCR = 205 ppm/^∘C for post-fired samples and HTCR = 520 ppm/^∘C and CTCR = 350 ppm/^∘C for buried in LTCC structures.     

Preliminary data on compatibility between thick film perovskite electrodes and PLZT films

The possible use of electrically conductive perovskites SrRuO₃, La(Ni_0.6Co_0.4)O₃ and (La_0.5Ca_0.5)FeO₃ as electrodes for PLZT ((Pb,La)(Ti,Zr)O₃ solid solutions) thick films was evaluated. As the ceramic electrode is placed between an alumina substrate and a PLZT thick film layer possible interactions between Al₂O₃ on one side and PLZT on the other and the chosen perovkites were studied. Both SrRuO₃ and LaNi_0.6Co_0.4O₃ reacted at 1000°C with Al₂O₃ forming SrAl₂O₄ and RuO₂ in the first case and LaAlO₃ and La₂NiO₄ in the second case. At higher firing temperatures reactions between La_0.5Ca_0.5FeO₃ and Al₂O₃ resulted in small quantities of an unknown phase or phases. The results of reactions of all three perovskites with PLZT were perovskite solid solutions incorporating ions from the conducting perovskites into the PLZT structure.     

Fe基体上Ni膜和Cu基体上Ag膜的膜内应力

直流电沉积法在Fe基体上制备Ni膜和在Cu基体上制备Ag膜,利用悬臂梁法在线测量了膜中的平均应力,并计算了膜内分布应力,且对膜内平均应力的实验结果与Thomas?Feimi?Dirac?Cheng(TFDC)电子模型理论估算结果进行了对比。结果表明,Fe基体上Ni膜的平均应力和分布应力均为拉应力,而Cu基体上Ag膜的平均应力和分布应力均为压应力。两种膜的内应力均由界面应力引起。对于相同的基体和镀膜,膜内平均内应力的理论估算值与实验值较接近。     

Influence of the contacts and firing process on the properties of thick film resistors on alumina and dielectrics

This paper describes the behaviour of thick film ruthenium resistors when printed and fired onto standard 96% alumina substrates and onto alumina substrates covered with a dielectric film during long-term thermal ageing. It was observed that the behaviour of the resistors on alumina and dielectric depends upon the firing process of the resistors and the kind of terminations. An analysis of the effects of thermal ageing was made as well as some SEM observations of diffusion processes between the resistor and its terminations.     

Degradation of NiCr/CuNiMn/NiCr films on alumina substrates

This paper addresses the aging behaviour of NiCr/CuNiMn/NiCr triple layers on Al₂O₃ ceramics at temperatures up to 200°C for film thicknesses d0.5 μm. Investigations of the film structure and the increase of resistance and its temperature coefficient during the annealing process and studies of the dependence of this aging drift on both the film thickness and the storage temperature have been carried out. Furthermore, the film stress and the effect of substrate bending on resistance have been measured. The results can be explained by the irregular film structure (columns and small bridges between them), which causes stress and current concentrations as well as local creeping, cracking and oxidation processes in the micro-bridges. They are compared with such for structurally homogeneous films on silicon wafers.     

Lamination of alumina membranes to polymer surfaces: thick, hard, transparent, crack-free alumina films on polymers with excellent adhesion

Hard and transparent alumina (Al(2)O(3)) films with thicknesses in the range of 500 nm to 5 μm were successfully formed on polymethylmethacrylate (PMMA) and polystyrene (PS) surfaces. Our process is based on a lamination of anodized aluminum membranes (AAMs) to the polymer surfaces, followed by chemical etching. Because of capillary force, molten PS and liquid PMMA precursor were successfully pulled into the nanopores (10 nm diameter) within the Al(2)O(3) layers and solidified by cooling or polymerization, respectively. Our resulting AAM-laminated surfaces exhibited excellent adhesion and surface mechanical properties similar to those of fused silica, remaining crack-free and transparent even with Al(2)O(3) thicknesses exceeding 1 μm.     

Microstructural investigation of Bi–Sr–Ca–Cu–oxide thick films on alumina substrates

The microstructure of Bi–Sr–Ca–Cu–oxide (BSCCO) thick films on alumina substrates has been characterized using a combination of X-ray diffractometry, scanning electron microscopy, transmission electron microscopy of sections across the film/substrate interface and energy-dispersive X-ray spectrometry. A reaction layer formed between the BSCCO films and the alumina substrates. This chemical interaction is largely responsible for off-stoichiometry of the films and is more significant after partial melting of the films. A new phase with f c c structure, lattice parameter a = 2.45 nm and approximate composition Al₃Sr₂CaBi₂CuO _x has been identified as reaction product between BSCCO and Al₂O₃. This revised version was published online in November 2006 with corrections to the Cover Date.     

Acoustic properties of alumina colloidal/polymer nano-composite film on silicon

Alumina colloidal/polymer composite films on silicon substrates have been successfully fabricated using the sol-gel method, in which the crystallite sizes of alumina are between 20 and 50 nm. The density and ultrasonic phase velocities in these films with different alumina ratios from 14% to 32% were measured at the desired operating frequency. We have proved that the density, acoustic phase velocities, and hence the acoustic impedance of the nano-composite films increase with the alumina content, which gives us another option of tailoring the acoustic impedance of the nano-composite film for making the matching layer of high-frequency medical ultrasonic transducers.     

A nonlinear electromechanical model for ferroelectric materials: application to soft-PZT thick films screen-printed on alumina substrate

Motivated by experimental observations made on soft-PZT/alumina cantilever bimorphs, a nonlinear electromechanical model is presented describing the characteristic phenomena of ferroelectricity: the dielectric hysteresis, the butterfly loop, and the ferroelastic hysteresis. This model uses a phenomenological formulation, written within the general framework of thermodynamics of irreversible processes. The one-dimensional formulation of the model is successfully validated using experimental data from the literature. The model is used to predict the electromechanical behavior of a PZT/alumina cantilever bimorph. The results of the simulations are very promising.     

Penetration depth variation in high quality YBaCuO thin films

We report results obtained on state-of-the-art YBCO thin films prepared by pulsed laser deposition on LaAlO ₃ substrates, using samples as similar as possible in two different experimental set-ups: a surface impedance measurement on 4000 Å thick films using a parallel plate resonator (10 GHz), and a far infrared transmission (100-400 GHz) measurement which requires thinner (1000 Å) samples. The measurements show a reduction of the penetration depth slope dMdT with improving quality of the thin films, which exhibit a low temperature scattering rate and residual surface resistance, comparable to single crystals. A linear fitting to the (T) experimental results yields d/dT=2 Å/K in both experiments in the low frequency limit.     

Fibre/matrix interactions in magnesium-based composites containing alumina fibres

An investigation has been made of composites with magnesium-based matrices CPMg, AZ61 and AZ91 reinforced with Safimax low-density (LD), standard-density (SD) and RF Saffil alumina fibres, using either a squeeze or a gas-pressure casting route. Detailed investigations of structural features have been made using SEM, TEM and EDX analysis. The overall extent of reaction between matrix and fibre was affected by the volume fraction of fibres and (locally) by the formation of metal channels between fibre bundles. Fibre microstructure and porosity are the key features which significantly influence the extent of chemical interaction. LD (Safimax) alumina fibres were fully reacted and cannot be employed to produce liquid-metal infiltrated composites, unless a method to stabilize or protect the fibres can be found. In the case of SD Safimax fibres, the metal/ceramic interaction produced a considerable penetration of magnesium into the fibres. However, there was negligible chemical reaction in composites containing RF Saffil alumina fibres.     

Ferromagnetic films deposited on nanochannel alumina

Interest in artificially grown nanostructures has grown enormously in the last few years because of the potential applications in the magnetic recording industry. In this work we present ferromagnetic resonance investigations performed on Fe films sputter-deposited on nanochannel alumina (NCA). These films form a network-like nanostructure on top of the walls that separate the pores. The geometry is fixed by the channel size, the porosity of the substrate and the film thickness. From the experimental results in NCA of 20 nm pore diameter we have found that thinner films (10 nm or less) are discontinuous and formed by isolated, partially oriented anisotropic particles. An average aspect ratio of ∼1.5 was estimated for the particles forming the film. As the film thickness increases the effective anisotropy (mostly shape anisotropy) tends to reach a saturation value for films thicker than 75 nm. For NCA substrates of larger pore diameter (100 nm and 200 nm pore size) the effective anisotropy is greatly reduced and even changes orientation for the thinner films. This behavior is interpreted as comming from a faster filling of the pores with the sputtered material in the substrates with smaller pore size. Received: 30 March 2000     

Infrared absorption in thick film resistors

Infrared absorption in polymer and glass-based thick film resistors has been measured between 400 and 1500 cm^–1. Sample structures are discussed on the basis of X-ray, Fourier transform-infrared and resistance-temperature data. It is shown that in polymer-based thick film resistors, the particulate phase is mostly responsible for the infrared absorption between 400 and 900 cm^–1, whereas the infrared absorption at higher wave numbers is related to the continuous phase. In glass-based thick film resistors, absorption is mostly determined by the highly doped glass. The results indicate that thick film resistors can be used as an absorbent coating in the 400–1500 cm^–1 region by suitable selection of the continuous and particulate phases.     

Junction formation in YBaCuO thin films by scanning probe technologies

A novel method of Josephson junction formation using atomic force microscopy (AFM) is presented. We have investigated surface modifications of YBaCuO films by using AFM with applied voltages. Ridge structures have been observed at the surface of YBaCuO at applied voltages between 4V and 10V, the narrowest ridge line width fabricated being 150nm. The mechanism of the formation of the ridge structure is discussed. Current-voltage characteristics of AFM modified microbridges in YBaCuO thin films have been measured and analyzed.     

Resonant Rutherford backscattering. Study ofa-axis YBaCuO films with very high crystallinity

Hybrid sputtering and the conventional dc-template sputtering methods were used to deposit highly crystallinea-axis films. The oxygen contents and disorder of the films were measured by the resonant Rutherford backscattering. The oxygen content of the films deposited by the hybrid sputtering depend on the deposition temperature. Films deposited at a low temperature have low oxygen content. The poor superconducting properties of these films may be due to the oxygen deficiency. The stoichiometry of the films deposited by the dc-template sputtering method was found to depend on the microstructure of the template. The disorder at the Ba and O sublattices of these highly crystallinea-axis films are uncorrelated.     

多孔阳极氧化铝膜的结构修饰研究

以5%草酸为电解液,温度控制在5℃左右,采用两步阳极氧化工艺制备出多孔氧化铝膜,在1 μm范围内获得了孔径为10～60nm的多孔结构.通过原子力显微技术分析氧化时间及热处理条件对多孔氧化铝膜结构的影响,阳极氧化3h后,在0.3μm2范围内获得了有序的纳米孔阵列,当氧化时间延长至24h,有序孔阵列范围增加至～1μm2.将在聚乙烯中经过超声振荡过的样品在600～700℃中热处理3h.研究结构表明,经过适当的热处理能有效改善多孔氧化铝膜的结构特性,X射线衍射分析结果证实经过结构修饰后的样品呈非晶态结构.