Advanced High-temperature superconducting components for microwave systems

The application of high-temperature superconducting thin films to microwave systems is expected to lead to major volume and weight savings as well as improved performance. To take full advantage of the properties that the new materials have to offer and justify the additional cooling equipment that accompanies the introduction of superconductivity, many HTS components will have to be integrated. In this paper some of the key microwave circuits that show great promise in this respect, such as multiplexers, circulators, and very narrowband filters, will be discussed and experimental results presented.     

Si(100)衬底上PLD法制备高取向度AlN薄膜

采用脉冲激光沉积法(PLD),以KrF准分子为脉冲激光源,Si(100)为衬底,同时引 入缓冲层TiN和Ti_0.8Al_0.2N,制备了结晶质量优异的A1N薄膜,X射线衍射(XRD)及反射 式高能电子衍射(RHEED)分析表明A1N薄膜呈(001)取向、二维层状生长.研究发现,薄膜 的生长模式依赖于缓冲层种类,直接在Si衬底上或MgO／Si衬底上的A1N薄膜呈三维岛状生 长;而同时引入缓冲层TiN和Ti_0.8Al_0.2N时,A1N薄膜呈二维层状生长.此外,激光能量密 度大小对A1N薄膜的结晶性有显著的影响,激光能量密度过大,薄膜表面粗糙,有颗粒状沉积 物生成.在氮气气氛中沉积,能使薄膜的取向由(001)改变为(100).     

Preparation and properties of YBa2Cu3O7 thin films on sapphire with Yttria-stabilized zirconia buffer layer

YBa₂Cu₃O₇ superconducting thin films were deposited onR-plane sapphire substrates with Yttria-stabilized zirconia buffer layer by laser ablation. The structure of the films was characterized by X-ray diffraction. Superconducting transitional temperatures as high as 90 K and critical current densities up to 2.2×10⁶ A/cm² (77 K) were achieved. The results of Auger depth profile showed that no obvious diffusion occurred between the substrate and the YBa₂Cu₃O₇ thin film.     

Shadowed Off-Axis Pulsed Laser Deposition of YBa2Cu3O7?x Thin Films

Using a shadowed pulsed laser deposition allows us to reduce the number of droplets on the YBa₂Cu₃O_7–x film surface obtained by pulsed laser deposition method. In this study, we present a new modification of pulsed laser deposition method: a shadowed off-axis pulsed laser deposition. The substrate surface lies in the plain defined by the laser beam. A rectangular shadow mask located between target and substrate reduce the quantity of large particles deposited from the diffusion flow. Such geometry allows us to carry out the laser plume scanning on the target surface for simultaneous one-step double-sided deposition films with a droplet-free surface. Both films had good superconducting properties.     

脉冲激光沉积法制备双层结构铜氧化物界面高温超导（英文）

在2008年发表的一篇经典工作中, Gozar等人报道了由绝缘性的La2CuO4和金属性的La1.55Sr0.45CuO4双层薄膜构成的体系存在界面超导.一个重要的有待回答的问题是该界面超导是否强健以及具有普遍性.在Gozar等人的工作中,铜氧化物双层结构是利用特制的氧化物分子束外延设备生长的,最大Sr掺杂量仅为0.47.在本工作中,我们首次利用脉冲激光沉积法制备了铜氧化物双层结构,并重复出了上述界面超导工作.在此基础上,我们将Sr的掺杂范围大幅扩展到1. 7 0,结果表明在由La2CuO4和过掺杂的La2-xSrxCuO4构成的双层结构中界面超导非常强健和普遍.值得一提的是,我们发现在x>0.8范围内存在一个新的界面超导区间.     

脉冲激光沉积技术制备超导铌薄膜及其特性研究

采用脉冲激光沉积技术(PLD)在硅衬底上制备超导Nb薄膜,并通过X射线衍射(XRD)、扫描电子显微镜(SEM)、高分辨X射线光电子能谱(XPS)、综合物性测量系统(PPMS)等测试分析手段,分别考察了不同激光能量、靶基间距、衬底温度对Nb薄膜晶体结构、表面形貌和电学性能的影响。结果表明,Nb薄膜在(110)晶向择优生长,并且随着激光能量的增加,薄膜的结晶质量逐渐提高;合适的衬底温度和靶基间距有利于提高Nb薄膜的结晶性能;在激光能量280 mJ、靶基间距5cm、加热盘温度650℃时制备所得Nb薄膜在(110)晶面半峰宽(FWHM)为0.39°,超导转变温度(Tc)为8.6K,且Nb薄膜具有良好的结晶性能和超导特性。     

硅基PtSi纳米薄膜制备及应用研究进展

PtSi红外探测器是一种重要的光电器件，在军事和民用方面均起着非常重要的作用。高质量硅基PtSi薄膜的制备是基础。本文介绍了溅射、分子束外延、脉冲激光沉积和激光分子束外延等制备PtSi薄膜的方法。并评述了PtSi红外探测器的最新应用研究进展及发展趋势。     

脉冲激光淀积法在Pt/TiO_2/SiO_2/Si(001)衬底上制备Pb(Ta_(0.05)Zr_(0.45)Ti_(0.50))O_3薄膜的铁电性质研究

用脉冲激光淀积方法在Ｐｔ／ＴｉＯ２／ ＳｉＯ２／ Ｓｉ（００１） 衬底上制备了掺Ｔａ 的ＰＺＴ 薄膜。此薄膜显示了理想的铁电性。漏电流特性表明这种异质结构中Ｓｃｈｏｔｔｋｙ 场发射机制起主要作用。扫描电镜形貌照片表明ＰＺＴ 薄膜结晶很好并且异质结构界面无明显扩散。     

Preparation of large-area high-quality YBCO thin films by pulsed laser deposition with Si heater and composite scanning of laser and target

We report on the successful preparation of large-area high-quality YBa₂Cu₃O₇ superconducting thin films by pulsed excimer laser ablation with a Si heater and composite scanning of laser beam and target. The Si heater, composite scanning of laser beam and target, and experiment results are described. The temperature variation of the Si heater was < ±0.5% in a 45×40 mm² area of 900–1000 °C. Films were deposited on LaAlO₃ substrates 35 mm in diameter. The thin films exhibited a thickness variation of ±2.5%; the superconducting properties wereT _c0=91×0.5 K andJ _c= (3.3±0.7)×10⁶ A/cm² at 77 K and zero magnetic field.     

Structure and dielectric properties of highly (100)-oriented PST thin films deposited on MgO substrates

High-quality Pb_0.4Sr_0.6TiO₃ (PST) thin films have been epitaxially grown on MgO (100) substrates at various substrate temperatures by the pulsed laser deposition (PLD) technique. Their crystalline phase structures and surface morphology were measured by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Their in-plane orientation was observed by the Phi scans on the (111) plane. Their dielectric properties were measured by a precision impedance analyzer. Results show that the perovskite phase was stable in PST thin film. The crystalline phase formation of the thin film depended on the deposition temperature. The phase formation ability and (100)-orientation of these films were increased with increasing deposition temperature. Both of the high tunabilities and low dielectric loss of the thin films show that the (100)-oriented PST is a potential material that can be used for tunable applications.     

Ba0.5Sr0.5 TiO3薄膜、Ba0.1Sr0.9 TiO3/YBa2 Cu3O7-δ异质薄膜的制备及介电性能研究

铁电钛酸锶钡(BSTO)薄膜具备十分优越的铁电/介电性能,在可调谐微波器件和动态随机存储器(DRAM)方面显示出十分诱人的应用前景.而YBa2Cu3O-δ(YBCO)高温超导薄膜作为其电极引入,明显降低了微波损耗,能够大大优化器件的性能.本文针对微波器件性能要求对比了各种常用基片的性能参数,描述了目前BSTO薄膜与BSTO/YBCO异质薄膜制备中存在的问题以及薄膜介电性能测试表征方法.利用脉冲激光沉积(PLD)技术成功制备出结构完整和质量较高的Ba0.5Sr0.5TiO3薄膜.同时,在1.2°斜切LaAlO3基片上研制有Ba0.1Sr0.9TiO3/YBa2Cu3O7-δ异质双层膜,在1MHz频率、77K温度条件下,其介电常数为1200,介电损耗为0.0045,±30V直流偏压时可调性达到60%,在液氮温度下表现出良好的应用前景.     

紫外脉冲激光淀积法制备Pb(Ta0.05Zr0.48Ti0.47)O3薄膜的铁电性质

用紫外脉冲激光淀积方法在Pt／TiO2／SiO2／Si(001)衬底上制备了La1-xSrxCoO3／Pb(Ta0.05Zr0.48Ti0.47)O3(PTZT)／La1-xSrxCoO3异质结构薄膜。发现底电极La0.25Sr0.75CoO3可以诱导PTZT薄膜沿(001)方向取向生长。在500kHz和5V的工作电压下铁电电容器La0.25Sr0.75CoO3/PTZT／La0.25Sr0.75CoO3经过5×1010次反转之后,仍保持其初始电极化的96％。此异质结构横截面的扫描电镜照片表明界面上没有明显的因化学反应导致的第二相存在。     

Properties of epitaxial, (001)- and (110)-oriented (PbMg1/3Nb2/3O3)2/3-(PbTiO3)1/3 films on silicon described by polarization rotation

Epitaxial (PbMg_1/3Nb_2/3O₃)_2/3-(PbTiO₃)_1/3 (PMN-PT) films with different out-of-plane orientations were prepared using a CeO₂/yttria stabilized ZrO₂ bilayer buffer and symmetric SrRuO₃ electrodes on silicon substrates by pulsed laser deposition. The orientation of the SrRuO₃ bottom electrode, either (110) or (001), was controlled by the deposition conditions and the subsequent PMN-PT layer followed the orientation of the bottom electrode. The ferroelectric, dielectric and piezoelectric properties of the (SrRuO₃/PMN-PT/SrRuO₃) ferroelectric capacitors exhibit orientation dependence. The properties of the films are explained in terms of a model based on polarization rotation. At low applied fields domain switching dominates the polarization change. The model indicates that polarization rotation is easier in the (110) film, which is ascribed to a smaller effect of the clamping on the shearing of the pseudo-cubic unit cell compared to the (001) case.     

薄膜型锂离子电池正极材料研究进展

简要介绍了近年来磁控溅射和脉冲激光沉积制膜技术在薄膜型锂离子电池正极材料制备方面的应用研究; 对制膜新工艺及新型正极材料的研究现状进行了概括,认为现阶段新型材料LiFePO4有希望成为薄膜锂电池正极材料的首选,并展望了薄膜型锂离子电池的发展前景.     

High-temperature superconducting microwave devices: Fundamental issues in materials, physics, and engineering

High-T _c superconductivity has generated a great deal of interest because of the challenges it presents in the fields of material science, condensed matter physics, and electrical engineering, and because of the potential applications which may result from these research efforts. Thin-film passive microwave components may become the first high-temperature superconducting (HTS) devices available for widespread use and commercialization. In this article, we review aspects of material science, physics, and engineering which directly impact high-T _c superconducting microwave devices and discuss issues which determine the performance of these devices. Methods of growing HTS thin films on large-area substrates, techniques for fabricating single-level HTS passive microwave components, and the relevant properties of high-T _c superconducting films are discussed, with a focus on thin films of the HTS material YBa₂Cu₃O_7–. Several known mechanisms for microwave loss in both the superconductor and the dielectric substrate are presented. An overview of the general classes of superconducting passive microwave devices is given, and representative microwave devices which have been recently demonstrated are described in detail. Examples of a select few HTS active microwave components are also presented. Potential microwave applications are illustrated with comparisons to current technology.     

Process parameters optimization for laser deposition of highT c superconducting thin films on Si and other substrate materials

Thin films of Y-Ba-Cu-O superconductor have been deposited on different substrates by pulsed excimer laser ablation from a superconducting pellet. The dependence of various process parameters such as substrate temperature, laser energy density, oxygen partial pressure, applied bias field and cooling rates on the quality of the films has been studied.     

脉冲激光制备硅基超薄PtSi薄膜

用脉冲激光沉制备了纳米级Pt/Si异质层,对激光退火形成超薄PtSi薄膜进行了研究,对于Pt、Si互扩散反应形成Pt2Si和PtSi的过程利用XPS进行了测试分析,通过XPS和AFM等分析测试手段对不同参数激光退火形成的PtSi薄膜的结构特性进行观测。我们获得了均匀的、超薄边疆的PtSi层且具有平滑的PtSi/Si界面。     

AlN薄膜的KrF准分子脉冲激光沉积

研究了采用脉冲激光沉积(PLD)技术在Si(100)衬底上AlN薄膜的制备及其性质。结果表明,衬底温度从室温到800℃的范围内,所得到的AlN薄膜为(002)择优取向的纤锌矿结构。随着衬底温度的升高,AlN薄膜从纳米晶结构转为多晶结构,同时表面微粗糙度上升。AlN晶粒呈柱状生长机制。     

Comparison of high-pressure dc-sputtering and pulsed laser deposition of superconducting YBa2Cu3O x thin films

Superconducting YBa₂Cu₃O_x thin films were deposited on NdGaO₃ (110) substrates using two different techniques: dc sputtering at high oxygen pressure and pulsed laser deposition. The structure, electrical properties, and surface morphology of the obtained films were compared. The superior crystal quality of dc-sputtered films fabricated at the same temperature and at oxygen pressure of the same range as for laser-deposited films can be explained by a lower deposition rate providing time for recrystallization processes. The re-evaporation becomes significant for dc sputtering at high deposition temperatures and results in Badeficient films. The high mobility of atoms on the surface of the growing film during laser deposition helps in the formation of smoothc-oriented areas of the film.     

Studies on nonvolatile resistance memory switching in ZnO thin films

Six decades of research on ZnO has recently sprouted a new branch in the domain of resistive random access memories. Highly resistive and c-axis oriented ZnO thin films were grown by us using d.c. discharge assisted pulsed laser deposition on Pt/Ti/SiO₂/Si substrates at room temperature. The resistive switching characteristics of these films were studied in the top-bottom configuration using current-voltage measurements at room temperature. Reliable and repeated switching of the resistance of ZnO thin films was obtained between two well defined states of high and low resistance with a narrow dispersion and small switching voltages. Resistance ratios of the high resistance state to low resistance state were found to be in the range of 2–5 orders of magnitude up to 20 test cycles. The conduction mechanism was found to be dominated by the Ohmic behaviour in low resistance states, while Poole-Frenkel emission was found to dominate in high resistance state. The achieved characteristics of the resistive switching in ZnO thin films seem to be promising for nonvolatile memory applications.