Fabrication And Characterization Of Strontium Barium Zinc Niobate Microwave Dielectric Ceramic Thin Films

The rapid development of microwave communication industry largely accelerates the study of microwave materials and devices. The miniaturization and high integration of the microwave frequency devices is the development trend of the communication devices. However, the minimum size of bulk devices isλ/4, which can not meet the requirement of miniaturization and high integration, thus the microwave dielectric ceramic thin film is prepared with many methods .As one of the dielectric thin films, the microwave dielectric ceramic thin film is applied in the fields of microwave integrated circuit and microwave integrated devices, which can be used as key materials of filters, resonators and dielectric substrate. Microwave dielectric ceramic materials with the characteristics of high dielectric constant, near-zero temperature coefficient of resonance frequency and lower crystallizing temperature compared with the bulk materials have a potential application value in the fields of satellite communication and mobile communication system.The substitution of Sr²⁺ to A site Ba²⁺ in Ba(Zn_1/3Nb_2/3)O₃ forms the (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃,which has the excellent dielectric property in the microwave dielectric ceramic materials: the high quality value Q is 3365, the dielectric loss is 0.69×10^-4, and temperature coefficient is -2.1×10^-6/℃at 3.842 GHz. (Ba_0.3Sr_0.7) (Zn_1/3Nb_2/3)O₃ have important potential application in the fields of satellite communication, radar, and mobile communication system because of its excellent dielectric proerties.Our group has studied ceramic thin films fabricated by radio frequency (RF) magnetron sputtering using stoichiometric (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃ as target. However, there exist many problems for these thin films, such as the composition difference between the target and the thin films (i.e., serious Zn-loss), a large number of oxygen-vacancies, poor crystallinity. In this paper, a Zn-enriched target comprised of a homogeneous mixture of 1mol (Ba_0.3Sr_0.7)(Zn_1/3Nb_2/3)O₃ and 1 mol ZnO was utilized to compensate the volatilization of Zn during the process of sputtering and annealing. The study of this paper concerns two aspects: firstly, RF magnetron sputtering technique and thermal annealing technique are employed to prepare the ceramic thin films, using a Zn-enriched target comprised of a homogeneous mixture of 1mol (Ba0.3Sr0.7)(Zn1/3Nb2/3)O₃ and 1 mol ZnO, X-ray diffraction (XRD), X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used to characterize the crystallinity, microstructure and surface morphology of the thin films.(1) The ceramic thin films were studied by X-ray diffraction (XRD), X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM), which were used to characterize the crystallinity, microstructure, and surface morphology of the thin films.(2) The cross-sectional SEM images verify that the growth rate decreases sharply, the thickness decreases from 3.10μm (pure Ar) to 1.38μm (O2/Ar ratio of 0.2:1) oxygen, because the thickness decreases from 3.10μm (pure Ar) to 1.38μm (O₂/Ar ratio of 0.2:1). The grain size decreased with heating. The surface RMS roughness of the films was reduced while the substrate temperature increased. The surface root-mean-square roughness of the thin films decrease with the increasing in the annealing temperatures. The surface RMS roughness of the films is reduced while the annealing time increases, however, the surface RMS roughness tends to increase when the annealing time increases further than 30 min.