Research On Growth Behavior Of Binary Alternating Doping Barium Strontium Titanate Films

Diversified kinds of film materials have come forth in recent decades. As one ofthe most important parts of film materials, barium strontium titanate (BST) has beenstudied and great achievements have been made. The improved sol-gel method isadopted for preparing BST films in this thesis. The technique has advantages of smallroughness, high speed, easy to control composition precision and is suitable formanufacture films with large area. In addition, cracking can be avoided and dielectricproperties can be improved by adding additives (PVP). Research in film growth is themost basic and the important part for it determines characteristics of the film. To thebest of our knowledge, vegetal behavior and mode of film are seldom studied. Firstly,theoretic growth model of film is constructed in this paper. Relationship betweentheoretic and actual growth model is studied by utilizing XRD and AFM. Relationshipbetween the growth pattern and dielectric properties is discussed after analyzingdielectric properties of film layer. The main contents of the thesis are summarized asfollows:1. Growth model of film is established. According to the existing theories andexperiences, Mg/K/Mg, Mg/Mg, K, K/K and BST/BST models are established. Themodels mainly vary with thickness and consistence to simulate vegetal behavior andmode of film. Advantages and disadvantages of each film are analyzed in the thesis aswell.2. Actual growth behavior of film is tested and validated. Use consistence of1%asprincipal part, and consistence of5%for optimization and contras, the surfacemorphology of8layers film is studied by XRD and AFM. The existing researchindicated that diffraction peak and surface morphology of Mg/K (100) alternationappear wavy change and surface roughness decreased with the increase of thickness.Surface roughness increases while the Mg/K (100) diffraction peak shifting to highangles. On the other hand, grain size and roughness increase when K/Mg sole doped(100) diffraction peak move towards small angles. The surface of pure BST becomesrougher when the diffraction peak moves to highAngle. 3. Growth behavior of film is tested and optimized. If the thickness of Mg/Kalternation is small, dielectric and tuning rate decrease with the increasing thickness.Otherwise the tuning rate appears wavy change with thickness, the regulation agreeswell with the measured results of XRD and AFM. Good dielectric performance appearswhen the film is composed of8-layer. Sole doping of K shows high dielectric tuningrate and dielectric loss, but comprehensive performance seems ordinary. Sole Mgdoping shows good comprehensive performance. Compared to pure BST film, soledoping and alternating dopping films have better comprehensive dielectric properties. Itcan be summarized that dielectric performance is tightly related to dielectric filmgrowth way. That is to say, K/Mg and Mg/Mg growth pattern is similar to each other,miscibility between the layers is excellent while grains grow not only uniform but alsotiny and the film has good dielectric performance; Mg/K/and K/K growth pattern aresimilar to each other, intersolubility between two types of film is poor, the grain growsso bulky and disorderly that the comprehensive dielectric property of the film is poor.