基于IBAD路线制备YBCO超导带材缓冲层的研究

发布时间：2018-05-15 13:29

本文选题：YBCO超导带材 + 离子束辅助沉积　；参考：《电子科技大学》2016年博士论文

【摘要】：YBa2Cu3O7-x(YBCO)高温超导带材具有优异的电学性能,在输电线缆、强磁体、电动机、限流器等领域有广阔的应用前景。为了获得高性能的YBCO超导带材,必须制备出高质量的缓冲层来为YBCO提供生长衬底。目前,缓冲层的制备过程中仍存在一些关键问题需要解决:如高质量的双轴织构、高的制备成本和缓冲层的均匀性等。因此,本论文致力于在金属基底上制备低成本、高质量、良好均匀性的缓冲层,主要内容如下:1、自主设计了低成本的溶液沉积平坦化(SDP)系统,利用该系统在哈氏合金(Hastelloy C276)基底表面制备Y_2O_3非晶薄膜,研究了热处理温度和涂覆层数对非晶薄膜的表面形貌和结晶性的影响,成功制备出5μm′5μm范围内表面均方根粗糙度(RMS)仅为0.2 nm的非晶薄膜,为IBAD-Mg O的生长提供了良好的衬底,然而Y_2O_3薄膜在热处理过程中可能出现结晶现象,并且在后续La Mn O3(LMO)模板层制备过程中,Y_2O_3会出现重结晶的现象。因此,本实验室在Y_2O_3薄膜中掺杂Al_2O_3来提高非晶薄膜的结晶温度,相比于Y_2O_3(500°C),Y_2O_3-Al_2O_3(YAl O)的热稳定性更高,最优化热处理温度范围更宽(480~540°C),在后续LMO层制备过程中没有出现重结晶现象。2、利用离子束辅助沉积(IBAD)技术在非晶薄膜表面制备Mg O织构层,在短样上成功制备出面外半高宽((35)w)2.4°左右,面内半高宽((35)(37))3.7°左右的Epi-Mg O/IBAD-Mg O薄膜。利用高能电子衍射仪(RHEED)实时监测IBAD-Mg O的双轴织构演化过程,发现双轴织构在形核阶段突然形成(薄膜厚度大约为2.2 nm)。R.T.Brewer等人提出的小岛级联理论能够解释IBAD-Mg O双轴织构形成的过程,基于该理论,利用一种两步法来加速IBAD-Mg O的双轴织构形成过程,使IBAD-Mg O在厚度仅为0.5 nm时便能获得双轴织构。利用自外延技术在IBAD-Mg O衬底同质外延了一层Mg O薄膜(Epi-Mg O),薄膜的表面形貌及双轴织构均得到了改善。成功制备出50 m长Epi-Mg O/IBAD-Mg O薄膜,薄膜的织构均匀性良好,面外半高宽和面内半高宽分别为3°左右和6°左右。理论上,双面YBCO能够使临界电流翻倍,从而产生更高的经济效益。因此,本论文设计了双面IBAD-Mg O缓冲层结构,为双面YBCO薄膜提供良好的生长衬底。克服了双面IBAD-Mg O缓冲层的制备技术难题,制备了50 m长双面Epi-Mg O/IBAD-Mg O薄膜,一面Mg O薄膜的(35)w和(35)(37)分别为2.8~3.2°和5.3~6.7°,另一面Mg O的(35)w和(35)(37)分别为2.6~3.3°左右和4.2~6°。3、采用低成本的中频反应磁控溅射法(MF)制备双面LMO模板层,并对该系统的加热装置进行改造,新的加热装置原理是将直流电通入缓冲层带材两侧,利用基带自身电阻产生的热量来给薄膜外延生长提供能量。新的加热方式可以提升温度的均匀性,并实现带材的快速升降温。经验证,MF-LMO的最大制备效率高达67 m/h。在最优化工艺下制备了20 m长双面LMO模板层,薄膜的双轴织构均匀性和一致性良好,一面的(35)w和(35)(37)分别为2°左右和4~5°,另一面的(35)w和(35)(37)分别为2°左右和5~6°。最终获得的YBCO带材两面的临界电流分别为180 A/cm-width和110 A/cm-width,两面总临界电流为290 A/cm-width,验证了双面缓冲层结构的技术可行性。4、通过将LMO模板层直接沉积在IBAD-Mg O薄膜表面的方法来简化缓冲层制备工艺,降低制备成本。XRD的q-2q扫描结果显示LMO薄膜沉积在IBAD-Mg O表面需要较高的生长温度(820°C)来克服LMO与IBAD-Mg O之间大的晶格应变能。最优化条件下制备LMO/IBAD-Mg O薄膜的面外半高宽和面内半高宽分别为3.5°和7.2°,最终缓冲层制备工序可降至3道,而国际通用的缓冲层制备工序则为6道,因此,该结构简化了缓冲层的工艺步骤,降低了制备成本。5、开发了新的IBAD织构化材料(Na F,Na Cl),与IBAD-Mg O相比,Na F与Na Cl具有以下优点:1、在涂覆层数为4层的Y_2O_3衬底上(5μm′5μm,RMS=8nm),Epi-Na F/IBAD-Na F((35)w=2°,(35)(37)=7.5°)与Epi-Na Cl/IBAD-Na Cl((35)w=2.1°,(35)(37)=8°)能够获得高质量的双轴织构,而IBAD-Mg O必须在RMS值小于2 nm的Y_2O_3衬底(涂覆层数大于16层)上才能够获得双轴织构;2、当离子源的离子束流为25 m A时,Na F和Na Cl获得双轴织构的沉积速率工艺窗口分别为0.08~2 nm/s和0.06~3.5 nm/s,而Mg O的沉积速率工艺窗口仅为0.06~0.12 nm/s。以上两个优点说明IBAD-Na F和IBAD-Na Cl具备制造难度低,工艺窗口宽的优点,适合双轴织构衬底的低成本快速制备。
[Abstract]:YBa2Cu3O7-x (YBCO) high temperature superconducting strip has excellent electrical properties. It has a broad application prospect in the fields of transmission cable, strong magnet, motor, current limiter and other fields. In order to obtain high performance YBCO superconducting strip, high quality buffer layer must be prepared to provide growth substrate for YBCO. At present, there are still some problems in the preparation process of the buffer layer. The key issues need to be solved: such as high quality biaxial texture, high preparation cost and uniformity of buffer layer. Therefore, this paper is devoted to the preparation of low cost, high quality and good uniformity buffer layer on metal substrates. The main contents are as follows: 1, the SDP system is designed independently, and the system is used in the system. Y_2O_3 amorphous film was prepared on the base surface of Hastelloy C276. The effect of heat treatment temperature and coating number on the surface morphology and crystallinity of amorphous films was studied. The amorphous thin film with a surface mean square root roughness (RMS) of only 0.2 nm in the range of 5 m '5 m was successfully prepared, which provided a good substrate for the growth of IBAD-Mg O, but Y_, however, Y_ The crystallization of 2O_3 films may occur during the heat treatment process, and the recrystallization of Y_2O_3 will occur during the preparation of the subsequent La Mn O3 (LMO) template layer. Therefore, this laboratory is doped with Al_2O_3 in the Y_2O_3 film to improve the crystallization temperature of the amorphous film, compared to Y_2O_3 (500 degree C), Y_2O_3-Al_2O_3 (YAl) has a higher thermal stability. The optimized heat treatment temperature range is wider (480~540 C) and no recrystallization.2 is found in the subsequent LMO preparation process. Mg O texture is prepared on the amorphous film surface by ion beam assisted deposition (IBAD) technology, and the outer half width ((35) w) and the half width ((35) (37)) of the Mg O texture are successfully prepared on the short sample, and the Epi-Mg O/I is about 3.7 degrees in the surface. BAD-Mg O film. Using high energy electron diffraction (RHEED) to monitor the evolution process of the dual axis texture of IBAD-Mg O in real time, it is found that the dual axis texture is suddenly formed at the nucleation stage (the thickness of the film is about 2.2 nm).R.T.Brewer et al. The small island cascade theory can explain the process of the formation of the IBAD-Mg O biaxial texture. Based on this theory, a kind of two steps is used. The biaxial texturing process of IBAD-Mg O is accelerated, and IBAD-Mg O can obtain biaxial texture at a thickness of only 0.5 nm. A Mg O film (Epi-Mg O) epitaxial layer of Mg O thin film (Epi-Mg O) is made on IBAD-Mg O substrate by self epitaxy technology. The surface morphology and biaxial texture of the thin film are improved. The thin film, thin film, thin film, and film are successfully prepared. The texture uniformity is good, the outer half width and the half width of the surface are about 3 degrees and about 6 degrees respectively. In theory, the double side YBCO can double the critical current, thus producing higher economic benefits. Therefore, this paper designs a double-sided IBAD-Mg O buffer layer structure to provide a good growth substrate for the double-sided YBCO thin film. The double-sided IBAD-Mg O is overcome. 50 m long double-sided Epi-Mg O/IBAD-Mg O thin film is prepared, and the (35) w and (35) (37) of Mg O film are 2.8~3.2 and 5.3~6.7, and the other Mg O (35) w and (35) (37) are left and right, respectively, and the low cost medium frequency reactive magnetron sputtering is used to prepare the double-sided template layer. The heating device is reformed. The principle of the new heating device is to connect the direct current into the strip of the buffer layer and use the heat generated by the self resistance of the baseband to provide energy for the epitaxial growth of the film. The new heating method can improve the uniformity of the temperature and realize the rapid rise and fall temperature of the strip. It is verified that the maximum preparation efficiency of the MF-LMO is high. The 20 m long double-sided LMO template layer was prepared under the optimal process. The uniformity and consistency of the dual axis texture of the film was good, the one side (35) w and (35) (37) were about 2 degrees and 4~5, respectively, the other side (35) w and (35) (37) were 2 degrees and 5~6 degrees respectively. The critical current of the final obtained YBCO strip was 180 A/cm-width and 110 A respectively. /cm-width, the total critical current of two sides is 290 A/cm-width, which validates the technical feasibility of the double-sided buffer layer structure.4. By depositing the LMO template layer directly on the surface of the IBAD-Mg O film, the preparation process of the buffer layer is simplified. The q-2q scanning result of the preparation cost.XRD shows that the LMO thin film needs a higher growth on the IBAD-Mg O surface. The temperature (820 C) can overcome the large lattice strain energy between LMO and IBAD-Mg O. Under optimal conditions, the outer surface half width of LMO/IBAD-Mg O thin film and the inner half width of surface half height are respectively 3.5 and 7.2 degrees, and the final buffer layer preparation process can be reduced to 3, and the international common buffer layer preparation is 6. Therefore, the structure simplifies the work of the buffer layer. A new IBAD textured material (Na F, Na Cl) has been developed in the process of reducing the cost of preparing.5. Compared with IBAD-Mg O, Na F and Na Cl have the following advantages: 1, on the substrate with a layer of 4 layers (35) (35) (37) (35), (35) (35) (37)) can be obtained. A high quality biaxial texture is obtained, and IBAD-Mg O must be able to obtain a dual axis texture on a Y_2O_3 substrate with a RMS value of less than 2 nm (the number of coating layers greater than 16 layers). 2, when the ion beam flow of the ion source is 25 m A, the deposition rate process window for the Na F and Na Cl is a dual axis texture. The art window is only 0.06~0.12 nm/s. above two advantages. It shows that IBAD-Na F and IBAD-Na Cl have the advantages of low manufacturing difficulty and wide process window, which are suitable for low cost and rapid preparation of dual axis texture substrate.

【学位授予单位】：电子科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TM26;O484

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