实现多层混合刻蚀薄膜大面积均匀的方法浅探

采用多层光刻工艺结合氩离子铣的混合刻蚀方法，刻蚀高Ｔｃ超导ＹＢａＣｕＯ／ＺｒＯ２（１００）薄膜图形，取得了较好的结果。在进行氩离子镜的工艺步骤中，使用普通氩离子铣设备（离子束斑极不均匀），但采取了一定的措施─－使被刻样品在刻蚀台座上可移动，模糊地实现了薄膜的相对＂大面积＂（直径φ≥２０ｍｍ）均匀刻蚀─－可同时刻蚀２～３片６ｍｍ×１０ｍｍ薄膜，并且被刻蚀部分表面起伏约在１０ｎｍ左右。图形样品的最小线条达２μｍ，其Ｔｃ、Ｊｃ人与刻蚀前薄膜的Ｔｃ、Ｊｃ相当，即：ＴＣ为８５～９０Ｋ，Ｊｃ～１０６Ａ／ｃｍ２（在７７Ｋ下）。     

Heat transfer in YBaCuO thin film/sapphire substrate system

The thermal boundary resistance at the YBaCuO thin film/Al₂O₃ substrate interface was investigated. The transparency for thermal phonons incident on the interface as well as for phonons moving from the substrate was determined. We have measured a transient voltage response of current-biased films to continuously modulated radiation. The observed knee in the modulation frequency dependence of the response reflects the crossover from the diffusion regime to the contact resistance regime of the heat transfer across the interface. The values of transparency were independently deduced both from the phonon escape time and from the time of phonon return to the film which were identified with peculiarities in the frequency dependence. The results are much more consistent with the acoustic mismatch theory than the diffuse mismatch model.We are grateful to A. Elantev for helpful discussion. We acknowledge the financial support of the Russian Scientific Council on the HTS problem (Project No. 90462).     

全化学法制备缓冲层和YBaCuO超导涂层

用化学溶液沉积法,尤其是金属有机物沉积法（MOD）制备第二代超导带材,包括缓冲层和YBaCuO涂层,在当前超导带材研究中具有重要的意义．因为其成本低、操作简单、便于规模化生产,可能成为制备高温超导带材最有前途的方法．文内详述了用化学气相沉积,化学溶液沉积,电泳共沉积以及超声雾化热分解等方法制备YBaCuO超导涂层的国内外进展,介绍了在LaAlO3单晶上以及金属基带上制备钙钛矿结构缓冲层的主要种类和特征,也介绍了当前研究的热点之一,导电缓冲层的作用、制备方法和研究进展．     

Influence of grain boundary weak links on the nonequilibrium response of YBaCuO thin films to short laser pulses

The transient voltage response in both epitaxial and granular YBaCuO thin films to 80 ps pulses of YAGNd laser radiation of wavelength 0.63 and 1.54 m was studied. In the normal and resistive states both types of films demonstrate two components: a nonequilibrium picosecond component and a bolometric nanosecond one. The normalized amplitudes are almost the same for all films. In the superconducting state we observed a kinetic inductive response and two-component shape after integration. The normalized amplitude of the response in granular films is up to five orders of magnitude larger than in epitaxial films. We interpret the nonequilibrium response in terms of a suppression of the order parameter by the excess of quasiparticles followed by the change of resistance in the normal and resistive states or kinetic inductance in the superconducting state. The sharp rise of inductive response in granular films is explained both by a diminishing of the cross section for current percolation through the disordered network of Josephson weak links and by a decrease of condensate density in neighboring regions.     

Photoinduced changes of the electrical conductivity in modified Y-Ba-Cu-O thin films

The conductivity changes of Y₁Ba₂Cu₃O_7– thin films under r.f. field and white light treatment at 77 K and under laser irradiation at 300 K were studied. The modified films were found to recover partially after prolonged laser illumination. The kinetics of photoactivation was investigated. The observed nonthermally induced changes were associated with free carrier trapping and local disordering of the lattice.     

Critical currents in YBaCuO ceramics

Magnetization measurements on a ceramic YBaCuO sample were carried out. TheM(H, T) dependence has demonstrated some peculiarities which we assume are connected withH _j1,H _j2,H _c1 fields. By analyzing the magnetization in the field region betweenH _j1 andH _j2 within the framework of the critical state model, one obtains the dependence of the intergranular critical current density on field and temperature.     

Ion beam and thermally-induced interface reaction between highT c superconductor thin film and metal overlayer

Ion beam and thermally-induced interface reactions between highT _c superconducting thin film of Y₁Ba₂Cu₃O_7−x and metal overlayer of Ag are studied with a view to control the interfacial property of contact resistance. The interface reaction is induced by 100 keV Ar⁺ ion beam with different ion dose values ranging from 5 × 10¹³ to 3×10¹⁴ ions/cm². The YBaCuO film-metal interface is characterized by using the small angle XRD to study the structural properties of the interfacial phases. The electrical property of the interface, specifically contact resistance, has been investigated for different dose values and thermal treatments. Three-probe vs four-probe configuration has been adopted to measure the contact resistance.     

Zero resistance states in modified Y-Ba-Cu-O system with transition temperatures above 135 K

Superconducting transition of minor-dispersed phase in modified YBa₂Cu₃O_7?δ samples is found to occur at around 140K. The amount of this minor phase is enough to provide zero resistivity above 135 K. The measurements of the electrical resistivity indicated that the material is stable, thermally recyclable and reproducible. X-ray analysis of the sample with the highestT _c shows a major phase with perovskite-like structure witha=3·820(1) Å;b=3·873(1) Å andc=11·659(2) Å along with several unidentified weak peaks. Magnetic measurements confirmed the mixed-phase nature with diamagnetic transition temperatures at 137,91 and 86 K. The minor phase responsible for superconductivity with zero resistivity above 135 K is about 0·4% of the bulk and its nature is still unidentified. The details of the preparation and chemical modification process and the results are presented.     

Cu—YBaCuO粉末复合材料组织与性能的研究

预期得到了一种具有较高强度而又不降低导电率的铜基粉末复合材料，选用超导陶瓷粉末ＹＢａＣｕＯ为强化相，以冷等静压，热挤压等粉末冶金方法研制了两种（Ｃｕ－５％ＹＢａＣｕＯ）和Ｃｕ－２０％ＹＢａＣｕＯ粉末复合材料，在常温和液氮温度下测试了这两种复合材料的力学性能与导电性能，研究表明，该复合材料的力学性能与导电性能，研究表明，该复合材料低温（７７Ｋ）时的力学性能优于室温，但导电率并没有改善，其原因在于所加     

Interface effects in YBCO/(Y-Pr)BCO multilayers, and the dimensionality of high-Tc superconductivity

Measurements on YBCO/(Y-Pr)BCO trilayers show that the depression of the transition temperature in ultrathin YBCO is accompanied by a decrease in the conductance of the layers adjacent to the interfaces. The lowering of the conductance seems to be primarily the result of charge transfer across the interfaces, and perhaps to some extent also of defects. The intrinsic properties of YBCO seem to change little or not at all as the thickness decreases from bulk down to that of a single unit cell.