Performance Improvement of Sandwich type High Temperature Superconducting Josephson Junctions by means of Microscopic Control of Engineered Interface Barrier

通过工程界面势垒的微观控制改进三明治型高温超导约瑟夫森结的性能

基本信息

批准号：
16560278
负责人：
TERADA Norio
金额：
$ 2.37万
依托单位：
Kagoshima University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2005
项目状态：
已结题

项目摘要

For the purpose to realize further improvements of performances and their reproducibility of sandwich type high temperature superconducting (HTS) Josephson Junctions, we have attempted to establish a fabrication process of ultra smooth (roughness < 2 nm) and thermally stable barrier layer on the surface of YBa2Cu3Oy (YBCO) HTS base electrode. In this project, 90 degree off-axis sputtering has been used for fabrication of the YBCO electrode, because of suitability of this method to large-area and uniform deposition. As the first step, for obtaining the ultra-flat surface of c-axis oriented YBCO films, growth conditions including growth temperature, gas pressure and gas-flow rates were optimized. A series of experiments revealed that a combination of sufficient supply of active oxygen and enhancement of surface diffusion on the growing surface should be effective to promote 2-dimensional growth as well as surface-smoothing. The diffusion could be promoted by an increase of growth tempera … More ture and reduction of defect density of substrate surfaces. The higher growth temperature usually resulted in the smoother surface of YBCO. The c-YBCO films grown on commercial SrTiO3 and LaSrAlTaO6 at 770 degree Celsius showed peak-to-valley roughness about 5 nm, which was close to the record of surface smoothness of c-YBC sputtered films. Since the growth temperature was limited with a re-evaporation temperature of some constituents, sufficient diffusions were hardly achievable over the mechanically and/or chemically, degraded surfaces of substrates, such as commercial ones. Usage of so-called step-and-terrace substrates which consist of atomically flat terrace and unit-cell height steps was effective to promote the diffusions and suppression of outgrowth of non-c-axis component of YBCO at a temperature below the re-evaporation. c-YBCO films grown on the step-and-terrace substrates at 750 degree Celsius exhibits both high superconducting critical temperature above 82 K and an excellent surface smoothness with a peak-to-valley roughness less than 2.5 nm, where one or two unit cell height steps were observed. This is one of the smoothest surfaces of c-YBCO sputtered films, and satisfies geometric requirement for surfaces of base electrode of sandwich type junction.For the flat c-YBCO obtained, surface engineering by means of Ar ion beam irradiation was adopted. Series of characterizations about crystalline, electronic structure of the engineered surfaces and a mechanism of re-crystallization of it in the subsequent high temperature process have been carried out. The in-situ experiments revealed initial thickness of the modified region with amorphous structure became thicker with an increase of kinetic energy of the impinging ions. The re-crystallization to the YBCO started at the interface between the amorphous and underlying YBCO regions and propagated to the surface. The surfaces engineered by ions with a low energy 〜 500 eV were easily converted to the YBCO structure by in-situ annealing at 630 degree Celsius for 1 hour. On the other hand, for the surface engineered with 1 keV ions, insulating feature remained even after an annealing at 730 degree Celsius for 3 hours. These results mean that combination of the engineering high energy irradiation and shortening of duration of deposition process of the upper electrode should be useful to fabricate the sandwich junctions. For the c-YBCO/interface-engineered barrier/c-YBCO sandwich type junctions, a RSJ type current-voltage characteristics has been successfully achieved by adopting the surface engineering of c-YBCO electrode with 1 keV ions, whereas the engineering with a low energy irradiation resulted in superconducting short.As mentioned, the fabrication processes of ultra-smooth surface of YBCO base electrode, and uniform and thermally stable engineered barriers for c-YBCO/interface-engineered barrier/c-YBCO sandwich type junctions has been established. Microscopic mechanism of the re-crystallization of the engineered region to superconducting phase has been clarified for the first time. Finally, Usefulness of these direct and microscopic controls of device-process has been demonstrated by realizing an excellent properties of the junctions. Less

为了实现进一步改善性能及其夹层型高温超导（HTS）约瑟夫森交界处的可重复性，我们试图在YBA2CU3OY（YBCO）HTS HTS基础电极的表面上建立一个超光滑（粗糙度<2 nm）和热稳定的屏障层的制造过程。在该项目中，由于这种方法适合大面积和均匀沉积，因此已使用90度离轴溅射进行制造。作为第一步，优化了以C轴为导向的YBCO膜的超流动表面，包括生长温度，气压和气流速率在内的生长条件。一系列实验表明，充足的活性氧供应和增强表面上表面扩散的结合应有效促进二维生长以及表面平滑。扩散可以通过增长温度的升高来促进……更多的底物表面缺陷密度和降低。较高的生长温度通常导致YBCO的光滑表面。在770度摄氏的商业SRTIO3和Lasraltao6上生长的C Ybco膜显示出约5 nm的峰值到谷状粗糙度，这接近了C-YBC溅射膜表面平滑度的记录。由于生长温度受到某种一致性的重新蒸发温度的限制，因此在机械和/或化学上降解的底物（例如商业降解的表面）上，足够的差异几乎没有成功。由原子平坦的露台和单位细胞高度步骤组成的所谓的阶段底物的使用有效地促进了YBCO的非轴轴成分的扩散和抑制，以低于重新蒸发的温度。在750摄氏度的步进式底物上生长的C Ybco膜既表现出高于82 K以上的高超导临界温度，又表现出极好的表面平滑度，峰值到valley粗糙度小于2.5 nm，其中一个或两个单位细胞的高度观察到一个或两个单位细胞的高度。这是c Ybco溅射膜的最平滑表面之一，并且满足了三明治型连接的基本电极表面的几何需求。对于获得的扁平C YBCO，采用了AR离子束辐照的表面工程。有关晶体，工程表面的电子结构的一系列字符以及在随后的高温过程中重结结的机制。原位实验表明，随着撞击离子的动能的增加，修饰区域的初始厚度变得更厚。重结合到YBCO的始于非晶和基础YBCO区域之间的界面，并传播到表面。通过低能量〜500 eV设计的离子通过630摄氏度的位于原位退火1小时，很容易转换为YBCO结构。另一方面，对于用1个keV离子设计的表面，即使在730摄氏度退火3小时后，绝缘功能仍保留。这些结果意味着，工程高能照射和上电极沉积过程持续时间的缩短的组合对于制造三明治连接应该很有用。 For the c-YBCO/interface-engineered barrier/c-YBCO sandwich type junctions, a RSJ type current-voltage characteristics has been successfully achieved by adopting the surface engineering of c-YBCO electrode with 1 keV ions, whereas the engineering with a low energy irradiation resulted in superconducting short.As mentioned, the Fabrication processes of ultra-smooth surface of YBCO base electrode, and uniform and已经建立了用于C YBCO/界面工程屏障/C Ybco三明治型连接的热稳定的工程屏障。已经首次阐明了工程区域重结合到超导阶段的微观机制。最后，通过意识到连接的出色特性，已经证明了这些直接和显微镜对照的有用性。较少的

项目成果

期刊论文数量（68）

专著数量（0）

科研奖励数量（0）

会议论文数量（0）

专利数量（0）

Fabrication of (Cu, C)Ba_2CuO_y superconducting thin films by RF magnetron sputtering

射频磁控溅射法制备(Cu,C)Ba_2CuO_y超导薄膜

DOI：
发表时间：
2005
期刊：
Institute of Physics (in press)
影响因子：
0
作者：
仁木栄;寺田教男;K.Ohki;K.Kikunaga;H.Wakamatsu
通讯作者：
H.Wakamatsu

In-situ characterization of Thermal Stability and Depth Profile of Electronic Structure of Engineered Surfaces of c-axis YBCO Films

c 轴 YBCO 薄膜工程表面的热稳定性和电子结构深度剖面的原位表征

DOI：
发表时间：
2004
期刊：
Institute of Physics 181
影响因子：
0
作者：
T.Okuda;N.Terada et al.;N.Terada;仁木栄;S.H.Kong;T.Okuda;S.Niki;K.Ohki;S.Miyanomae;K.Ohki
通讯作者：
K.Ohki

Fabrication of (Cu, C)Ba2CuOy superconducting thin films by RF magnetron sputtering

射频磁控溅射法制备(Cu,C)Ba2CuOy超导薄膜