MOCVD Research On YBCO Double-sided Superconducting Thin Films

YBa2Cu3O7-?(YBCO)double-sided high-temperature superconducting(HTS)thin films have important application in HTS microwave devices fabrication,but current preparation methods cannot meet the following requirements at the same time:(1)low cost;(2)high efficiency;(3)in-plane homogeneity and good double-sided consistency.This leads to the high price and suppling shortage of YBCO double-sided thin films,which greatly hinders the research progress of superconducting devices with low insertion loss and high sensitivity.Thus,it is of great significance to prepare high quality YBCO double-sided thin films at low cost and high efficiency.For solving this problem,a Metal Organic Chemical Vapor Deposition(MOCVD)system was designed to study the preparation of YBCO double-sided thin films.The details are as follows:(1)A MOCVD system has been designed and the preparation of 2-inch double-sided YBCO thin films has been studied.Firstly,a deposition device,which was composed of a planetary substrate turnplate and a U-shaped shower head,was designed.Double-sided simultaneous preparation of multiple YBCO thin films was realized by inserting turnplate in the U-shaped shower head,which significantly improved the preparation efficiency.Then,the gas flux distribution in the U-shaped shower head was optimized,and the consistency of both sides of YBCO thin films was improved.The test results showed that the 2-inch double-sided films prepared in this way had good in-plane and double-sided consistency as well as good superconductivity(critical current density Jc=2.2-2.4 MA/cm2(77 K,0 T),microwave surface resistance Rs=0.323 m?(77 K,10 GHz)).Finally,the preparation cost and efficiency were calculated.The efficiency of the 2-inch 500 nm thickness double-sided YBCO films prepared by this method was as high as 16 minutes per piece,and the principle cost(excluding substrate)is as low as 45 RMB per piece.(2)The effects of substrate temperature and metal organic sources ratio on the YBCO thin films deposited on LAO substrates were researched.The research of substrate temperature showed that there were many cavities on the thin films at low temperature and the thin films decomposed and the texture deteriorated at high temperature.At 845?,Jc was optimized up to 3.0 MA/cm2.The research of metal organic sources ratio showed that there were impurity particles in the thin films which led to the decrease of Jc when the ratio of Cu and Ba sources deviated from the ideal ratio.In a proper range,the change of Y-source ratio had little effect on the texture and Jc of the thin films.When the concentrations of Y,Ba and Cu were 294 mg/10 ml,1385 mg/10 ml and 755 mg/10 ml respectively,the Jc was the largest,reaching 2.8 MA/cm2,(3)The effects of substrate temperature and deposition rate on the YBCO films deposited on MgO substrates were researched.The research of substrate temperature showed that the c-axis orientation temperature of YBCO thin films deposited on MgO substrates was about 845? and a-axis oriented grains appeared when the substrate temperature was low.Using the same MOCVD process as depositing YBCO on LAO substrates,YBCO thin films deposited on MgO substrates had a larger Aco(1.44°)and was non-oriented in plane.The research of deposition rate showed that the decrease of deposition rate in the early stage improved the c-axis orientation(?? reduced to 1.29°).Meanwhile,the in-plane orientation changed from non-orientation to two orientations co-existed of which one paralleled to MgO[100]and the other paralleled to MgO[110].