Microwave Tuning Characteristics Of The New Technology Of Bst Thin Films Studied

Barium Strontium Titanate (BaxSr1-xTiO3, shorten as BST) thin films have great prospect in microwave tunable device. This thesis is mainly a preliminary study on technic of improving BST thin films. The Sol-Gel method is a technic which is convenient, cheap, and compatible with semiconductor technology and are widely used for BST thin film deposition. Whereas BST film prepared by normal Sol-Gel technic has the limitation of strong stress and high density of cracks and holes. Therefore, modified methods such as introducing thermal pretreatment are studied to grow high-performance films. On this basis, the annealing temperature is studied.The morphology of four thermal pretreatment models are studied by atomic force microscopy (AFM), including both single and double layer thin films with one or two layer thermal pretreated. Through the analysis on the surface roughness, grain size and size uniformity, the effect of thermal pretreatment on film structure, stress and film-substrate interface lattice matching were discussed.Four thermal pretreatment methods (Ⅰ), (Ⅱ), (Ⅲ), (Ⅳ) were designed, tested, and discussed. The different surface morphologies caused by these four thermal pretreatment methods were studied by AFM as well. The mechanism of how the thermal pretreatment methods affect the BST thin film surface morphology was analyzed.The dielectric properties of BST thin film is studied at low frequency. Four samples prepared by the (Ⅰ), (Ⅱ), (Ⅲ), (Ⅳ) thermal pretreatment methods were measured. The effect of thermal pretreatment on tunability and dielectric loss were analyzed through comparing the four samples'dielectric properties. Recommendations were given on choosing proper thermal pretreatment method for optimized tunability and dielectric loss.To reduce the dielectric loss with tenability maintained, two thermal pretreatment methods were chosen for further study on annealing temperature fine adjustment. Through surface morphology and dielectric properties analysis, the difference caused by varying annealing temperature were measured and discussed to find the most appropriate annealing temperature. Furthermore, the electron structure of a four layer thin filmthermal pretreated by method (Ⅱ) was studied by X-ray photoelectron spectroscopy (XPS).