The Preparation And Properties Of Mg Doped PST Ceramics And Thin Films

The ferroelectric materials possess excellent dielectric, piezoelectric, ferroelectric, pyroelectric and nonlinear polarization properties and have been widely used in many fields, such as the dynamic random-access memory, the infrared sensor, the tunable microwave device. It could be used in the tunable oscillator, the tunable filter and the phase shifter in phased-array radar or other related area in the microwave field for its excellent nonlinear dielectric response. Materials that applied in the microwave field should contain higher tunability as well as lower dielectric loss. At present the related research mainly concentrates on the perovskite structural materials, including SrTiO₃, (Ba,Sr)TiO₃ (BST) and (Pb,Sr)TiO₃ (PST). PST has the high tunability and quite low dielectric loss. PST and BST have a similar Curie temperature which could be adjusted by changing the ratio of Pb/Sr. Compared with the BST, PST only has one phase transition, and exhibits lower crystallization temperature, which make it suitable for integrate component. At present, the research on PST is at the start stage. Its performances are not as good as needed in the application.Mg doping (Pb,Sr)TiO₃ ceramics were prepared by the solid sintering process , and the Mg doping PST thin films were prepared by the radio frequency magnetron sputtering deposition method. XRD, SEM, Impedance Analyzer, High Resistance Analyzer and Ferroelectric Analyzer were applied to analyze the microstructures, dielectric properties and the ferroelectric properties of both the ceramics and thin films.The Mg-doping effect on the microstructure and performance of them were also discussed.Pure tetragonal perovskite phase were obtained in ceramics when quantity of Mg doped was 0⁰.08mol%. The results showed that Mg²⁺ substituted Ti⁴⁺ and the unit cell distorted, simultaneously dreased the c/a. When x≤0.02, the Mg²⁺ substituted Ti⁴⁺ and expanded the volume of unit cell. When x≥0.02, the dopant introduced the extrinsic oxygen vacancy and volume of the unit cell decreased while the dopant increase. Mgdoping can suppress the growth of the grain. Compound flaw (MgTi +VO) will be found,When the Mg2+ substitutes the Ti4+, the changed of Ti4+ to Ti3+ is restrained. This process could reduce leak current, dielectric loss and the dielectric constant; when x>0.05, the substitution introduced excessive flaws, and the leak current and dielectric loss increased. The lowest value of leak current and dielectric loss was achieved right at the point of 0.05mol%. The leak current we obtained here was 0.2045pA, and the dielectric loss was 0.00262, while the dielectric constant went to 238.It was found that the crystallization of the Mg doped PST thin films prepared on the ITO glass by the radio frequency magnetron sputtering deposition method starts at the temperature of 450°C and finishes at 600°C. The crystallization was spontaneous nucleant process. Suitable amount of Mg doping could balance the electric charge of PST and enhance the crystallization. When the sputtering power was low, these thin films obtain lower density which could absorb the stress caused by crystallization. So the bilayer thin films which using the low density layer as the buffer layer were prepared. These bilayer thin films with different content of Mg possess the close grain size. The bilayer thin films exhibited the perfect insulating property.The compound flaw reduced the partial polarized electric filed which caused by the intrinsic oxygen vacancies, and made the soft mode "hardening" degree decrease; at same time enhance the tunability of the PST thin films. We got the maximum value of tunability of 17.5% at the point of x=0.03.