Dielectric Properties Of Barium Strontium Titanate Composite Thin Films Prepared By Pulsed Laser Deposition

Barium Strontium Titanate(Ba_xSr_1-xTiO₃, BST) is a ferroelectric material that having excellent dielectric properties. Its high dielectric constant, low dielectric loss, high pyroelectric coefficient, high dielectric tunability, the Curie temperature can change because of Ba/Sr ratios different, these excellent performance make it widely used in the tunable microwave devices, infrared imaging detector, a dynamic random access memory, a phase shifter radar, etc. Microelectronic technology is constantly developing and the preparation technology is continuously improving, small and highly integrated microdevices began to receive widespread attention. BST thin film device has broad application prospects due to its exceptional electrical and optical properties, however, high dielectric loss and large high leakage current density limit its development.In order to obtain barium strontium titanate composite films that having excellent dielectric properties, this Paper has concentrated on several aspects and the main results and conelusions can be summarized as following:1. We fabricated Ba_0.6Sr_0.4TiO₃ and Bi_1.5Mg_1.0Nb_1.5O₇ ceramic target use the solid-phase reaction method. We use XRD to measure the BST and the BMN targets, the results show that the BST and BMN are pure-phase polycrystalline structure. The BMN target has been prepared by powder embedded sintering method and excessive proportion method to avoid the losses of Bi element during the preparation of BMN target.2. BST thin film, BST/BMN/BST multilayer thin films and BMN/BST bilayer thin films are prepared by pulsed laser deposition?PLD? method on Pt substrate. By changing the deposition condition, for example, substrate temperature, oxygen pressure, the influence in film properties including physicality and electric properties are investigated.3. Through the analysis of thin films prepared under different conditions, we find that different temperature and oxygen pressure have significant effect on crystallinity and surface morphology. BST thin films are prepared at different substrate temperatures, according to the electrical properties tests, the BST thin film has the best dielectric properties at the deposition temperature of 700 °C. BMN/BST bilayer thin films are prepared at different oxygen pressure and BMN/BST bilayer thin films have the best dielectric properties when the oxygen pressure reaches 15 Pa.4. The BST thin film and the BST/BMN/BST multilayer thin films were investigated using XRD, AFM and electric properties were also tested. BMN film as inserted layer can effectively reduce the dielectric loss of BST thin film. Although the tunability from 69.8% down to 26.7%, however, the figure of merit?FOM? increased from 34.9 to 44.5. Meanwhile, the leakage current density of the multilayer film is significantly reduced.5. The BMN film as buffer layer and the specific relationship between the dielectric properties and the thickness ratio of the BMN thickness to the BMN/BST total thickness was investigated. With increasing the thickness of the BMN, the tunability and dielectric loss of the BMN/BST composite film are gradually reduced. By comparing the FOM value, we find that FOM has a maximum value?41.7? when the thickness ratio is 0.5. With the increasing thickness of BMN film, the leakage current density is gradually decreased.