STO/YBCO集成薄膜的脉冲激光沉积及性能研究

【作者】 李德红；

【导师】 刘兴钊； 李言荣；

【作者基本信息】 电子科技大学 ， 材料物理与化学， 2003， 硕士

【摘要】 SrTiO3(STO)薄膜在其居里温度附近（~40K）具有介电常数随电场强度变化而变化的性质，同时STO在10GHz以下介电常数没有频率色散性。而YBa2Cu3O7-x(YBCO)高温超导薄膜具有微波表面电阻极低的性质，Rs（10GHz,77K）<1mΩ，并且，STO和YBCO晶格结构和化学相容性均匹配良好。因此，STO/YBCO集成薄膜可用于制作滤波器、移相器、谐振器等微波可调器件。本论文主要研究STO/YBCO集成薄膜的生长，为微波可调器件的研制奠定基础。采用脉冲激光沉积技术在LaAlO3(001)(LAO)基片上生长YBCO、STO以及STO/YBCO集成薄膜，系统研究了基片温度、基片表面状态、氧分压、激光能量密度、脉冲重复频率等工艺参数对薄膜表面性能、结晶情况的影响，优化了YBCO、STO薄膜生长的工艺参数，运用AFM、SEM、XRD等分析手段表征薄膜的微观性能，分析结果表明：薄膜表面平整、结晶良好、C轴织构。实现了STO薄膜的准二维层状模式生长，在10μm范围内，STO薄膜的表面粗糙度RMS为0.77nm。感应法测试表明YBCO高温超导薄膜超导转变特性良好，Tc0>90K，△Tc<1K。为了测量STO薄膜的介电性能，做成平板电容器和叉指电容器两种结构的电容器。采用HP4284A LCR测试仪及四端对测试技术，测量电容器性能。所制备的STO薄膜在77K、100kHz的测试条件下，对于平板电容器结构，当电场从0增加到53.6KV/cm时，介电常数从1437降到902，调节率达到38%，介电损耗为1.06%。对于叉指电容器结构，当外加直流偏压为40V时，调节率为21%，介电损耗低至0.25%。观察到了平板电容器结构下C-V曲线中正反偏压下曲线不对称，最大值出现在-1.3V的现象，并采用串联电容模型进行了解释。更多还原

【Abstract】 The dielectric constant of SrTiO3(STO) thin films is voltage-dependent near the curie temperature Tc (about 40K) . And no dispersion in εis observed in STO at frequencies up to 10 GHz.YBa2Cu3O7-x(YBCO) high temperature superconducting thin film has very low microwave surface resistance. The typical value of Rs（10GHz,77K）is smaller than 1mΩ. In addition, Similarities in crystal structure and chemical compatibility between STO and YBCO open up the possibility that the unique properties of each of these films can be combined to develop an array of tunable microwave devices with novel applications such as filters, phase shifters and resonators. The major task of the dissertation is the growth of YBCO/STO for the fabrication of microwave devices.The STO, YBCO and STO/YBCO thin films were deposited on LaAlO3 (001)(LAO) substrate by pulsed laser deposition(PLD). The effects of deposition parameters, such as the substrate temperature, the of target-substrate distance, laser energy density, on the properties of the thin fillms were systematically studied. The surface morphology of the thin films was investigated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Under the optimized condition, the surfaces of the thin films were smooth. The root mean square roughness (rms) of STO thin film was 0.77nm in the range of 10μm. The step-flow growth mode of STO thin film was achieved. The X-ray diffraction (XRD) results showed that both STO and YBCO thin films were c-axis oriented. The superconducting transition properties of YBCO thin films were excellent, Tc0 >90K,ΔTc<1K. In order to demonstrate the dielectric properties of STO thin film, the sandwich-type capacitors and interdigitated capacitors were fabricated. The properties of capacitors were measured using an HP4284A LCR meter at 77K under 100kHz. The measurement results from sandwich-type capacitors showed that the dielectric constant decreased from 1437 to 902 when the electrical field increased from 0 to 56kV/cm.The tunability was 38% and the dielectric loss was 1.06%.The asymmetry on the C～V curve was observed. It was attributed to the formation of series capacitance by the STO thin films and the interface between STO and the bottom electrode. The measurement results from interdigitated capacitors demonstrated that the tunability is 21% when the bias is 40V and the loss is 0.25%.更多还原