高温超导YBCO薄膜及其制备

概述了高温超导YBCO(Y1Ba2Cu3O7-x)薄膜的基本性质、应用及制备技术的发展。介绍了脉冲激光沉积(PLD)与磁控溅射(MS)等的基本原理、工艺特点和最新发展情况。YBCO薄膜应用于超导电子器件中表现出优良的性能,如超导量子干涉仪(SQUID)等。     

准分子激光溅射法制备高温超导薄膜机理研究的新进展

本文简要介绍准分子激光溅射法制备高温超导薄膜的实验技术。重点阐述了近年来由大量实验研究所揭示出的激光溅射及成膜过程的一些基本特点和规律。同时,对准分子激光制膜保成份蒸镀这一独特优点的机制进行了深入的讨论。     

3英寸双面YBCO薄膜的MOCVD制备研究

制备大面积双面YBCO超导薄膜有助于器件集成的发展。基于自研金属有机化学气相沉积(MOCVD)系统在3英寸铝酸镧基片上制备了性能优异的YBCO超导薄膜。使用扫描电子显微镜(SEM)表征了薄膜表面形貌和厚度,结果显示薄膜双面形貌一致,薄膜表面大部分平整,有少量孔洞。双面厚度接近,分别为533 nm和565 nm。X射线衍射(XRD)测试结果表明在大面积薄膜上成分分布均匀,除了(400)-Y₂O₃和LAO基片衍射峰以外,只存在尖锐的(00l)-YBCO衍射峰,薄膜双面面外扫描半峰宽低于0.3°,面内扫描半峰宽低于0.944°且仅有四个相距90°的独立尖峰,说明薄膜沿基片外延质量好。在77 K温度下分布式临界电流密度(J_c)测试结果表明薄膜具有良好载流能力,双面J_c>2.4 MA/cm²,面内均匀性和双面一致性高。在77 K,10 GHz的条件下,使用蓝宝石谐振器测试得到薄膜的微波表面电阻(R_s)为0.188 mΩ。结果表明自研MOCVD系统能够制备高质量...     

高温超导薄膜的激光制备技术及其展望

本文评述了激光溅射方法制备高温超导薄膜的特点和优势,探讨了溅射和成膜过程的基本机理,展望了激光技术在高温超导薄膜的低温制备、显微制版等超导微电子工艺中的广阔应用前景。     

Tl,Hg系高温超导薄膜制备研究

介绍了南开大学在实用Tl和Hg系高温超导薄膜方面的研究工作.在Tl系高温超导研究领域, 利用磁控溅射和后退火两步法在LaAlO3,(001)衬底上制备出高质量的TI-1212和TI-2212超导薄膜,超导临界转变温度Tc分别为92 K和106 K;在两步法的基础上,利用两次后退火,得到Tl,Bi-1223超导薄膜,超导临界转变温度Tc可以达到110 K;同时,利用阳离子置换反应技术,在Tl-1212和T1-2212超导薄膜基础上得到Hg-1212超导薄膜,利用Tl-2223超导薄膜作为先驱膜,得到Hg-1223超导薄膜,结果显示,Hg-1212和Hg-1223超导薄膜的临界转变温度Tc可分别高达124 K和132 K.为满足T1系高温超导薄膜的微波应用需求,分别在LaAlO3、蓝宝石、氧化镁(MgO)衬底上制备出2英寸双面Tl-2212超导薄膜,该超导薄膜具有均匀的超导特性,薄膜超导特性优良,为制备高温超导微波无源器件提供了基础.     

YSZ／Si上溅射BSCCO高温超导薄膜的工艺参数优化

本文研究了利用ＹＳＺ膜作缓冲层Ｓｉ衬底上溅射ＢＳＣＣＯ高温超导薄膜的生长工艺，分析了生长条件对Ｂｓｃｃｏ高温超导相的影响，并提出了ＹＳＺ／Ｓｉ上制备相ＢＳＣＣＯ膜的工艺参数。     

高温超导薄膜电子显微结构的研究

本文报导了超导实验室用Ｈ９０００ＮＡ分析型电镜观察高温超导薄膜的结果，表明：激光淀积的ＹＢＣＯ薄膜易于出现非超导的大颗粒，提高了薄膜的表面微波电阻。但工艺若掌握得好时可生成单晶薄膜，适用于无源微波器件。     

大面积双面高温超导薄膜研究进展

大面积双面YBa2Cu3O7-δ高温超导薄膜具有优异的微波电学性能,在高端微波器件与电路中有着重要的应用。本文主要结合我们的工作介绍国内外大面积双面超导薄膜的研究工作进展,并着重结合器件应用要求进行相关讨论。     

YBCO超导薄膜侧馈H天线实验研究

利用ＹＢＣＯ／ＹＳＺ超导薄膜制做了侧馈的Ｈ天线，实验表明，与相同的银膜侧馈Ｈ天线相比，相对效率在ｘ极化方向上提高了９．３ｄＢ，在ｙ极化方向上提高了１３．６ｄＢ。     

Metal organic chemical vapor deposition of superconducting YBa2Cu3O7-x thin films

The discovery of YBCO superconductors has stimulated a great deal of scientific and technological research into thin films of these materials. Because the MOCVD technique is known to produce high quality films in the III/V and II/VI material groups, our approach has been to apply the method to superconducting thin films. Thin films were grown in a vertical high speed (0–2000 rpm) rotating disk reactor. The source materials were metalβ-diketonates kept at temperatures in excess of 100° in order to obtain growth rates of 0.3 to 0.5μm/hr. The precursors were transported to the chamber with a nitrogen carrier and injected separately in order to avoid any gas phase reactions. The chamber pressure was maintained at 76 Torr with an oxygen partial pressure of 38 Torr. A resistance heater was used to keep the substrate temperature at 500° YBa₂Cu₃O_7-x films were deposited simultaneously on a variety of substrates such as (100) MgO, (1-102) sapphire, (100) SrTiO₃ and (100) YSZ. Full XPS spectra were collected for the binary oxides. The scans demonstrate the existence of Y₂O₃, BaO, and CuO with the correct valence state for the metallic species. Energy dispersive analysis of x-ray (EDAX) was used to determine film compositions by comparing EDAX spectral intensity to a known superconducting standard. Appropriate changes were made in the precursor flows to correct the stoichiometry. The as-grown films were dark brown and semi-transparent. Cross-sectional SEM photomicrographs revealed an ordered columnar structure. After annealing at 950–980° however, the films on (100) SrTiO₃ appeared dull black and opaque. The surface morphology exhibited smooth large plate-like grains. X-ray data clearly display an orthorhombic phase, with c-axis perpendicular to the substrate surface. Four point resistance measurements for films on (100) SrTiO₃ show the onset of superconductivity at 90 K with a complete loss of resistance at 88 K. This sharp (≤2K) transition shows the high quality of these MOCVD grown YBCO films and are the first reported results from a large area (2 × 50 mm substrates) commercial reactor.     

Preparation of 3 Inch Double-Sided YBa2Cu3O7-X High Temperature Superconducting Thin Films

Owing to its excellent electrical property,YBCO thin film is much better than metal in the application for microwave devices. It makes the devices smaller, lighter, and with higher quality factor and lower insertion loss. YBCO thin film has attracted attentions for many years. Aiming at the uniformity and property of 3-inch double-sided YBCO thin film, the following aspects is considered in this dissertation:     

Effect of substrate smoothness on the microstructure of YBa9n2Cu3O7−x/Y2O3/YBa2Cu3O7−x trilayers

Transmission electron microscopy was used to analyze the microstructure of YBa₂Cu₃O_7−x/Y₂O₃/YBa₂Cu₃O_7−x trilayer structures deposited by off-axis sputtering on MgO substrates with varying degrees of roughness. Substrate surface hillocks with a peak-to-valley height of about 4.5 nm were found to contribute to strain that extended through the film and disrupted the smoothness of the Y₂O₃ layer. In some cases, these hillocks served as nucleation sites for yttria precipitates. Such defects may seriously jeopardize the realization of weak-link Josephson junctions.     

LaNiO3 and Cu3Ge contacts to YBa2Cu3O7-x films

Metallization of high-T_c superconductors using low resistivity metal oxides and Cu-Ge alloys has been investigated on high quality pulsed laser deposited epitaxial YBa₂Cu₃O_7-x (YBCO) films. Epitaxial LaNiO₃ (LNO) thin films have been grown on YBCO films at 700°C using pulsed laser deposition. The specific resistivity of LNO was measured to be 50 μΩ-cm at 300K which decreases to 19 μΩ-cm at 100K indicating good metallicity of the LNO films. The contact resistance of LNO-YBCO thin film interface was found to be reasonably low (of the order of 10^-4Ω-cm² at 77K) which suggests that the interface formed between the two films is quite clean and LNO can emerge as a promising metal electrode-material to YBCO films. A preliminary investigation related to the compatibility of Cu₃Ge alloy as a contact metallization material to YBCO films is discussed. The usage of other oxide based low resistivity materials such as SrRuO₃ (SRO) and SrVO₃ (SVO) for metallization of high-T_c YBCO superconductor films is also discussed.     

Preparation of high Tc (Yb,Y)Ba2Cu3O7-δ thin films by co-evaporation from effusion cells

We have prepared superconducting thin films of (Yb,Y)Ba₂Cu₃O_7-δ by evaporation of copper, ytterbium or yttrium, and barium fluoride from Knudsen effusion cells. A simple two chamber vacuum system produced stable evaporation rates of 5–10 nm/min using various Knudsen cells without realtime feedback control. Excellent stoichiometry was obtained in the films by optimizing the deposition of Cu from a dual filament cell, Yb from a single filament cell and Y and BaF₂ from high temperature cells. Films were deposited mainly on SrTiO₃ substrates at temperatures ranging from 120 to 600° C and O₂ partial pressure up to 1.5 ⋻ 10⁻⁵ Torr. Post deposition anneals in O₂ and O₂ + H₂O produced films with room temperature resistivities as low as 227μΩ-cm andT _c (R = 0) at 91 K. Films were characterized using x-ray diffractometry, Rutherford backscattering spectrometry, energy dispersive x-ray analysis, scanning electron microscopy as well as electronic transport measurements.     

Improved barium fluoride process YBa2Cu3)7-x films via post-anneal monitoring

The continuous monitoring of the conversion, of Y, Cu and BaF₂ precursors to form superconductor thin films has been achieved using a fluorine-specific-ion electrode immersed in an effluent gas-washing cell. High-quality thin films of YBa₂Cu₃O_7-x deposited on NdGaO₃, LaA10₃ and LaGaO₃, have been produced by limiting the wet oxygen annealing phase of the post-deposition anneal. When the films were over-annealed in humidified oxygen the superconducting transition temperature as measured by inductive methods and the crystal quality, determined by x-ray rocking curves were degraded.     

Dislocations and flux pinning in YBa2Cu3O7

The dislocation structures of bulk textured and epitaxial thin film YBa₂Cu₃O₇ superconductors are examined. Correlations between increases in flux pinning and dislocation densities are noted. A model for flux pinning by individual dislocations is presented. This gives a treatment of strain induced effects and effects of normal state region interactions. It is shown that the values of pinning predicted are in line with experimental observations.     

MgO缓冲层对Si衬底上制备Fe3Si薄膜性能的影响

采用磁控溅射方法和热加工工艺在n型Si衬底上溅射不同厚度的MgO层并制备Fe-Si薄膜层,退火后形成Fe3Si/MgO/Si多层膜结构.利用MgO缓冲层对退火时Si衬底扩散原子进行屏蔽,并分析MgO层对Fe3Si薄膜结构和电学性质的影响.通过X射线衍射仪(XRD)、扫描电子显微镜(SEM)和四探针测试仪对Fe3Si薄膜的晶体结构、表面形貌、断面形貌和电阻率进行表征与分析.研究结果表明:当MgO层厚度为20 nm时生成Fe0.9Si0.1薄膜,当厚度为50,100,150和200 nm时都生成了Fe3Si薄膜,生成的Fe3Si和Fe0.9Si0.1薄膜以(110)和(211)取向为主.随MgO缓冲层厚度增加,Si衬底扩散原子对Fe3Si薄膜的影响减小,Fe3 Si薄膜的晶格常数逐渐减小,晶粒大小趋向均匀,平均电阻率呈现先增大后减小趋势.研究结果为后续基于Fe3 Si薄膜的器件设计与制备提供了参考.     

Nucleation and Growth of b-Axis Oriented PrBa2Cu3O7-x Thin Films on LaSrGaO4 (100) Substrates

Good quality a-axis oriented thin films of YBa₂Cu₃O_7-x may be grown by the use of a PrBa₂Cu₃O_7-x (PBCO) layer as a template. Here we present a detailed study of the nucleation of the PBCO layer, explaining the orientations observed. It is determined that the wavy surface of a LaSrGaO₄ (LSGO) (100) substrate consists of the {101} planes by observing cross-sectional transmission electron microscopy images of the interface between the PBCO film and the substrate. The images and selected area diffraction patterns show that a mixed cand b-axis oriented PBCO layer was initially grown on the substrate, followed by pure b-axis oriented PBCO growth. We explain that the c-axis oriented growth is the result of the growth of the PBCO (019) planes on the LSGO (101) planes. We conclude that the nucleation and growth of the PBCO films at the initial stages depends on the crystallographic plane of the substrate surfaces, however, as the film grows further, the kinetics of the deposition process favors b-axis oriented growth.     

Study of the optical features of YBa2Cu3O7-x films by SEW spectroscopy

The results of YBa₂Cu₃O_7-x films on SrTiO₃ investigation by far infrared surface electromagnetic waves (SEW) amplitude and phase spectroscopy at temperatures 80–350 K are presented. Strong SEW absorption at frequency 142 cm^?1 has been observed. The origin of the observed absorbtion is proposed to be concerned with slab- phonons in YBa₂Cu₃O_7-x. The optical constants of the films have been obtained. Also has been determined, that only the imaginary part of the SEW refraction index changes when the film transits into superconducting state, while the real part remains unchanged.