| For the sake of the excellent microwave transmission properties of high temperature superconductor(HTS) YBa2Cu3O7-x(YBCO) epitaxial thin films, YBCO has been one of the perfect materials,which can highly reduce the microwave devices size and enhance its performance.The microwave devices, e.g.microwave filters,made of YBCO working in liquid nitrogen at atmospheric pressure possess high quality factor(Q-factor),low insert loss, small size,light weight,etc.Therefore,YBCO epitaxial thin films were researched intensively and deeply.The research works of our rap group were aiming the microwave filters' great demand for high quality YBCO epitaxial thin films.We always applied ourselves to the preparing of double-sided 2″YBCO epitaxial films by photo-assisted MOCVD method.In this paper,the photo-assisted MOCVD system for the growth of one-sided 2″YBCO epitaxial films was designed and installed.And then,a series of research were done about the growth technological process and the uniformity of larg area YBCO films。Comparing with quartz chamber,stainless steel chamber has multi-advantages,such as good sealing,mature mechanical workout, non-frangibility,and Flexible design etc.Thereby,based on some work on photo-assisted MOCVD with quartz chamber,this paper designed a new photo-assisted MOCVD system with a stainless reactor.In this system, precursor ovens with novel seal structure was designed,it can prevent the condensation of precursor vapor(Y and Cu) onto the upper cove.The susceptor and substrate was heated by more large power tungsten-halogen lamps,which were placed inside the reactor chamber.Novel and efficient water-cooled lampshade was designed and manufactured.It can prevent the lights from baking to each other,and lead to the life extension of lamps. Besides,based on some experiments,a new short stainless reactor was redesigned to solve the serious problems such as the swing of rotating shaft and the condensation,caused by too high of chamber,of precursor vapor on the lower part of reactor wall.As a result,repeatable preparation of YBCO epitaxial films by the photo-assisted MOCVD system designed and assembled by us was realizedA "substrate temperature window"(TS window) for purely c-axis oriented YBCO films was found,based on many times repeated experiments with the same airflow and pressure.This TS window is 800～830℃at total pressure of 4.6 torr and oxygen pressure of 2.8 torr.Lower temperature will lead to a-axis crystal grains,and higher temperature will lead to film decomposed or hardly depositon.Therefore,during the large area film deposition,the uniformity of illumination and accurate temperature control is a key factor who directly impact on the crystal quality uniformity of the films. Thereby,computer simulation of illumination intensity distribution for parallel line light sources was adopted.The arrangement of lights was optimized through computer-assisted.This improved the optical power density distribution lighting on 2″substrate surface.Experiments proved that this kind of word is very important for 2″and larger area film deposition.The airflow and air density near and upper the substrate is the key factor affecting the film growth rate there for most CVD reactors.The thickness uniformity of large area film is base on the airflow and air density distribution. In this paper,thickness distribution of 1″YBCO film growth on LAO substrate irrotated.Combining with the computer simulation of airflow and air density distribution,the thickness uniformity of large area YBCO film fabricated by photo-assisted MOCVD was discussed,and the basic method was proposed.During this study,1″purely c-axis YBCO epitaxial films were successfully fabricated by photo-assisted MOCVD system,on rotary LaAlO3 (100)(LAO) substrate with well crystalline quality uniformity.The thickness can be controlled from 0.2μm to 2μm,with difference of±10%.For 1″thin YBCO films(about 0.6μm),repeated experiments proved that JC of whole film are larger than 1 MA/cm2(0T,77K).The JC value of typical samples were 1-3 MA/cm2,and RS value were less than 0.4 mΩ. For 1″YBCO thick films(1.5μm),a preliminary result indicated that JC values were about 0.18MA/cm2(0T,77K),RS value is about 21 mΩ(10GHz, 77K)。By the same photo-assisted MOCVD system,c-axis YBCO films with well crystalline quality uniformity on 2″LAO substrates were also succesfully grown.The feasibility for large area YBCO deposition was adequately proved.The thikness distribution of 2″YBCO films was nonuniform caused by the nonuniform airflow distribution in this reactor. Film thicknesses at the edge of 2″YBCO films were thiner(about 300 nm) than that at the center(about 500 nm).And JC values at the edge were higher [3 MA/cm2(0T,77K)]than that at the center[1.8 MA/cm2(0T,77K)].The RS value at the center of this YBCO sample was about 0.5 mΩ(10GHz,77K).
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