| High temperature superconductor (HTS) YBCO possesses very high critical current intensity and low surface resistance values (Rs), its Rs is 2-3 magnitude order lower than that of Cu. The microwave filters made of YBCO possess a few strong points, such as low insert loss, high sensitivity and small in size and thus are considered to be the"ideal microwave filters". Making use of the kind of filters can greatly reduce band resources, power of communication equipment and inter-signal interference. Double-sized 2 inches HTS YBCO film with extremely high quality provides the basic material for HTS microwave filters. At present, there is no such technique entitled with independent property right for producing in large amount 2 inches YBCO films at home. YBCO epitaxial films grown by photo-assisted MOCVD technique possess high quality crystal, a thickness of several microns, and extremely fast growth rate. This thesis has made an attempt to study the epitaxial technique of doubled-sized 2 inches YBCO films by using the photo-assisted MOCVD and produced high-quality double-sized 1 inch YBCO films. Besides it has analyzed and processed the hill-like deposition, populating the surface of purely c-axis oriented YBCO epitaxial films made by MOCVD.This thesis has designed two kinds of photo-assisted MOCVD reactors, with one for vertical air current intake and the other for canted intake. A three-dimensional computer simulation for air flow patterns and temperature from the two reactors has been conducted and results thus obtained have been illustrated and compared. With two self-designed and assembled MOCVD systems, experiments for one-sided 1 inch YBCO films have been done in the respective reactors and the growth conditions have been optimized respectively. The films grown in the two reactors under optimal growth conditions have been compared in detail, finding that the orientation of 1 inch YBCO films grown in the reactor of vertical intake is uneven, with the center of the film a-axis oriented and the edge of the film c-axis oriented, resulting in poor quality of the superconductors. While the orientation and thickness of 1 inch YBCO films grown in the reactor of canted intake is quite even, resulting in high quality of the superconductors. Mean value of Jc may be1.5MA/cm2 or even above possibly and its even degree may be above 90%. The surface resistant value (Rs) can be below 0.5m?.The present thesis has also analyzed the forming process of the hill-like depositions populating on the surface of the purely c-axis oriented YBCO epitaxial films, made by MOCVD and investigated the techniques for removing the hill-like depositions. With long time experimental observation, analysis has been made on the shape and composition of the hill-like depositions populating on the surface of the purely c-axis oriented YBCO epitaxial films, which are with different thickness and length of grown-time. An attempted conclusion has been made that the liquid deposition comes into being along with the forming of the epitaxial films and the deposition exists in the form of liquid drop, which will remain on the surface of the film when the latter grows thicker and thicker. With the temperature dropping, the substances inside of the liquid drop will finally and gradually crystallized, forming the hill-like depositions, which stick to the surface of the purely c-axis oriented YBCO epitaxial films. The attachment of hill-like deposition to the surface of the films is not very strong so that it can be removed easily simply by polishing. The thesis also conducts a contrastive study on the characteristics of 1 inch YBCO films before and after the deposition is removed, finding that polishing almost exerts no effect on the characteristics of the YBCO epitaxial films and thus YBCO epitaxial films made by photo-assisted MOCVD can be applied to practice, after the deposition has been removed by polishing. The present thesis has also discussed the producing techniques of the double-sided photo-assisted MOCVD YBCO films and holds that these films can grow in two ways: one is that the two sides of the films grow simultaneously, the other is that the two sides grow side by side. As to the former way of growing, the grown-time is short and the differences between the characteristics of the two sides are slight, but it is hard to put into practice since a re-designed photo-assisted MOCVD reactor is required. While as to the latter way, the grown-time is comparatively long and the differences are relatively big, but it can be easily applied by using the existing equipment. At a result, the second producing technique has been employed in the present thesis to produce double-sided YBCO epitaxial films.The substrate temperature of tow sides when grown 1 inch double-sides YBCO films by tow-step method were analyzed and compared. Generally, the first-grown side of the 1 inch double-sided YBCO film is always a-axis oriented, while the latter-grown side is always c-axis oriented, resulting in poor superconductor characteristics of the former side, when the substrate temperature of the tow sides were same. Both sides of the double-sided YBCO film are purely c-axis oriented and thus both sides are with good superconductor characteristics while the substrate temperature of the first-grown side was higher than that of the latter-grown side. The Jc value of thus produced double-sided 1 inch YBCO films is always above 1.5MA/cm2 and the value of Rs is unusually below 1m?.
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