在有40nm厚的PrBa_2Cu_3O_7过渡层的(100)SrTiO_3基片上生长了YBa_2Cu_3O_7超薄膜,典型的厚度为2,6,10个原胞层.X射线衍射表明薄膜取向都是C轴垂直于膜面.原子力显微镜观察发现YBa_2Cu_3O_7超薄膜具有层状和螺旋两种生长模式,并且在6个原胞层的生长阶段观察到螺旋位错,而类似的生长特征并没有出现在PrBa_2Cu_3O_7过渡层中.实验结果表明,在 10个原胞层范围内,薄膜的超导转变温度和临界电流密度对厚度有很强的依赖关系. YBa_2Cu_3O_7 thin films were grown on (100) SrTiO_3 substrates with a 40nm-thick PrBa_2Cu_3O_7 transition layer, with typical thickness of 2, 6 and 10 protoplasm layers.X-ray diffraction showed that the C-axis was perpendicular to the film surface. Atomic force microscopy revealed that the YBa_2Cu_3O_7 thin film had both layered and helical growth patterns, and helix dislocations were observed in the growth stages of 6 primitive cells, while similar growth characteristics did not appear in the transition layer of PrBa_2Cu_3O_7.Experimental results showed that In the range of 10 primary layers, the superconducting transition temperature and the critical current density of the films have a strong dependence on the thickness.