关于YBCO薄膜过热现象的研究

在用YBa₂Cu₃O_z(YBCO)种膜液相外延生长Nd_1+xBa_2-xCuO_z(NdBCO)厚膜的过程中，YBCO晶体在高于熔点的温度下保持不熔化并且起到了外延种子的作用.采用高温金相显微镜,我们实时观察YBCO薄膜的熔化过程，发现了超导氧化物薄膜的过热现象，并且结合XRD极图的分析和Ba-Cu-O熔体的不润湿性现象合理解释了YBCO形成过热的机制.另外，通过对具有不同微观结构的YBCO薄膜熔化行为的横向比较，研究YBCO薄膜品质对于其过热度的影响，并用半共格界面能理论很好地解释了AFM和XRD分析及实时观察熔化过程的实验结果. 关键词： 过热 YBCO薄膜 熔化形核     

Microstructure of YBCO thin film and its effect on superheating

Previously, we have reported a superheating phenomenon of a YBa₂Cu₃O_x (YBCO) film and studied its mechanism. In this work, we investigated the influence of microstructure on the superheating of a YBCO thin film. Different melting behaviors were observed in situ from YBCO thin films with varied microstructures by using high-temperature optical microscopy (HTOM). These films with different degrees of crystallinity were also characterized by atomic force microscopy (AFM) and X-ray diffraction (XRD). It was found that the crystalline structure features of the seed film have a great influence on the degree of superheating and the melting behavior. A high-quality film with a low fraction of interface defects is believed to be responsible for the high superheating. On the basis of the experimental results from HTOM, AFM, and XRD, the melting and superheating behaviors associated with the film defect structure are well interpreted in terms of the semi-coherent interface-energy theory. PACS 68.35.Md; 68.47.Gh; 68.55.Ac     

CaO buffer layer for the growth of ZnO thin film

We report the effect of CaO buffer layers on the structural properties of sputter-grown ZnO thin films. X-ray diffraction patterns indicated that enhanced crystallinity and alleviated compressive strain in the ZnO thin film were achieved by inserting a very thin CaO buffer layer between ZnO and the sapphire substrate. The interface was investigated by high-resolution transmission electron microscopy, and the result showed that the growth of CaO on the sapphire substrate follows the Stranski–Kristanov mode. The mechanism for the control of crystallinity and strain in the ZnO thin film was discussed, and was found to be strongly related to the growth mode of the CaO buffer layer.     

Effect of interface layer on growth behavior of atomic-layer-deposited Ir thin film as novel Cu diffusion barrier

Growth and nucleation behavior of Ir films grown by atomic layer deposition (ALD) on different interfacial layers such as SiO₂, surface-treated TaN, and 3-nm-thick TaN were investigated. To grow Ir thin film by ALD, (1,5-cyclooctadiene) (ethylcyclopentadienyl) iridium (Ir(EtCp)(COD)) and oxygen were employed as the metalorganic precursor and reactant, respectively. To obtain optimal deposition conditions, the deposition temperature was varied from 240 to 420 °C and the number of deposition cycles was changed from 150 to 300. The Ir film grown on the 3-nm-thick TaN surface showed the smoothest and most uniform layer for all the deposition cycles, whereas poor nucleation and three-dimensional island-type growth of the Ir layer were observed on Si, SiO₂, and surface-treated TaN after fewer number of deposition cycles. The uniformity of the Ir film layer was maintained for all the different substrates up to 300 deposition cycles. Therefore we suggest that the growth behavior of the Ir layer on different interface layer is related to the chemical bonding pattern of the substrate film or interface layer, resulting in better understand the growth mechanism of Ir layer as a copper diffusion barrier. The ALD-grown Ir films show the preferential direction of (1 1 1) for all the reflections, which indicates the absence of IrO₂ in metallic Ir.     

Photon-induced switching and tunneling phenomena in a YBCO thin film junction

In the persistent photoconductivity (PPC) phenomenon, illumination of a YBa₂Cu₃O_6.5 thin film junction with a 1mW He−Ne laser leads to the decrease of the critical voltage (similar to the threshold voltage). The decrease of the critical voltage was reversed by illumination with incandescent light. The critical voltage across the junction was experimentally decreased and increased by alternating illumination between He−Ne laser and incandescent light. We also observed visible quenching of the photo-induced state using a 5mW He−Ne laser. Finally, the threshold behavior of the junction was destroyed by illuminating it with incandescent light.     

Intrinsic Josephson effects in 60-K phase YBCO thin film mesas

We fabricatedc-axis oriented meas on YBa₂Cu₃O_7−δ thin films. Columnar structures with an area of 20×20 μm² and a depth of 0.1 μm were formed on oxygen deficient films with a critical temperature (T _c ) of 64 K or less. The devices showed hysteretic I–V curves without any branches. The dependence of the critical current density on the temperature nearT _c is explained by the Ambegaokar-Baratoff relation.     

Chalcogen-based thin film transistor using CuInSe2 photo-active layer

We propose chalcogen-based photo-thin film transistor (P-TFT) using CuInSe₂ (CIS) homo-junction. By using a tri-layer process, we fabricated n- and p-type CIS films. Optical and electrical properties of the fabricated CIS films are measured to be suitable for homo-junction. For the fabrication of a P-TFT, n-type CIS generating higher photo current was used for a channel layer whereas p-type CIS with higher carrier density was used for source and drain. The fabricated transistor exhibited typical transistor operation of p-channel enhancement mode and current increase with light.     

Layer-by-layer growth of MgO thin films controlled by inserting a TiN seed layer using an in-situ pulsed laser deposition

Completely (200)-oriented MgO films were grown on Si(100) with insertion of a TiN seed layer by pulsed laser deposition (PLD). Compared with the conventional direct ablation of a metal Mg or ceramic MgO target, we successfully demonstrated an effective way to improve the crystallinity of MgO thin films. By using TiN as a seed layer, high-quality MgO films with an atomic-scale smooth surface of about 0.55 nm (Ra) were obtained. Moreover, it is found that the quality of MgO films was independent of the thickness of the TiN seed layer. The improved crystalline quality of the MgO films was attributed to the layer-by-layer growth mode during the deposition of MgO films, which was monitored in-situ by reflection high energy electron diffraction (RHEED). PACS 68.55.Jk; 81.15.Fg     

表面等离子共振金/钯复合膜氢敏传感器

提出了一种新颖的钯(Pd)/金(Au)复合膜表面等离子共振氢敏结构,与单一Pd膜氢敏传感器相比,具有可靠性好、灵敏度高和响应度大等特点。利用表面等离子共振理论建立了Au/Pd复合膜氢敏传感器的数学模型,并对Au/Pd复合膜氢敏传感器的灵敏度进行了数值模拟。数值模拟结果表明:基于Au(2nm)/Pd(20nm)复合膜氢敏传感器所获得的最佳灵敏度比单一Pd(20nm)膜氢敏传感器提高了49 4%。     

Wetting and reactive thin film growth

The wetting process of the GaN(0 0 0 1) surface by Ga is studied in situ in real time by low energy electron microscopy and diffraction. The reversibility of the phase transitions in the wetting layer is examined in detail and the consequences for the growth of GaN layers by reaction with ammonia and activated nitrogen are discussed. It is concluded that the growth of smooth (0 0 0 1)-terminated GaN layers may be considered as quasi-liquid phase epitaxy.     

Low-temperature MOVPE growth of ZnO thin films by using a buffer layer

ZnO thin films have been grown on a-plane (1,1,−2,0) sapphire substrates by metalorganic vapor phase epitaxy (MOVPE) at low substrate temperature of 350 °C. It is showed that the crystal and electrical quality of the thin films was improved by using a ZnO buffer layer. The photoluminescence (PL) measurements indicate that the ZnO thin films grown at such a low substrate temperature have a strong UV emission.     

基于氧化镍背接触缓冲层碲化镉薄膜太阳电池的研究

采用电子束蒸发法制备了NiO薄膜,并对其作为碲化镉薄膜太阳电池背接触缓冲层材料进行了相关研究.NiO缓冲层的加入使得碲化镉太阳电池开路电压显著增大.通过X射线光电子能谱测试得到的NiO/CdTe界面能带图表明NiO和CdTe的能带匹配度很好.NiO是宽禁带P型半导体材料,在电池背接触处形成背场,减少了电子在背表面处的复合,从而提高电池开路电压.通过优化NiO薄膜厚度,制备得到转换效率为12.2%、开路电压为789 mV的碲化镉太阳电池.研究证实NiO是用来制备高转换效率、高稳定性碲化镉薄膜太阳电池的一种极有前景的缓冲层材料.     

Preparation of YBCO film for microwave filter using a hybrid route

Pure (0 0 l)-textured CeO₂ buffer layers were deposited on single crystal r-plane Al₂O₃ (1–102) substrate by a hybrid process which was combined with magnetron sputtering for the seed layer and metal–organic deposition for the subsequent layer. Strongly c-axis oriented YBCO films were deposited on the CeO₂ buffered r-cut Al₂O₃ (1–102) substrates. Atomic force microscope and scanning electronic microscopy results show that the prepared buffers and YBCO films are relatively dense and smooth. The critical current of the YBCO films exceeds 1.5 MA/cm² at 77 K with the superconducting transition temperature of 90 K. The surface resistivity is as below as 14 μΩ at 1 GHz frequency. The results demonstrate that the hybrid route is a very promising method to prepare YBCO films for microwave application, which can combine the sputtering advantage for preparing of highly c-axis oriented CeO₂ buffer layers and the advantages of metal–organic deposition with rapid processing, low cost and easy preparation of large-area YBCO films.     

Enhanced fatigue property of PZT thin films using LaNiO3 thin layer as bottom electrode

A highly (100)-oriented metallic LaNiO₃ film was prepared directly on a Si substrate by a simple metalorganic decomposition (MOD) technique using lanthanum nitrate and nickel acetate as the starting sources. Subsequent Pb(Zr,Ti)O₃ (PZT) thin films deposited on the LaNiO₃-coated Si substrate were obtained by a modified sol–gel method. It was found that the PZT thin films began to form a single perovskite phase at a low annealing temperature of 530 °C, and exhibited highly (100) orientation. A ferroelectric capacitor of Pt/Pb(Zr,Ti)O₃/LaNiO₃/Si annealed at 600 °C displayed a good P-E hysteresis characteristic and was fatigue-free even after 10¹¹ switching cycles. Received: 25 May 2000 / Accepted: 9 August 2000 / Published online: 30 November 2000     

Improved performances in low-voltage-driven InGaZnO thin film transistors using a SiO2 buffer layer insertion

Al (5 nm)/Ga-doped ZnO (GZO, 100 nm) double-layer films were prepared at room temperature by magnetron sputtering. It is found that the crystal structure of GZO is degraded due to the existence of Al layer. Semiconductor transport behavior is observed in GZO and Al/GZO films in the temperature range of 80～360 K. As opposed to that of GZO, the resistivity of Al/GZO shows a significant decrease with increasing the temperature from 320 to 360 K. To understand the temperature dependent resistivity, Al (5 nm)/GZO film was annealed in vacuum in the temperature range of 398～573 K. High-resolution TEM observations reveal that Al grains become more and more isolated as the annealing temperature increases. The decreasing resistivity above 320 K for the Al/GZO system is considered to be caused by the substitution of Al atoms for Zn atoms at the interface, showing an improvement in the transmittance with over 90 % especially at 398 K.