Preparation And Dielectric Properties Of Oriented PST Thin Films By Magnetron Sputtering

Ferroelectric materials have promising application due to their excellent dielectric, piezoelectric, ferroelectric, pyroelectric and nonlinear polarization properties. The property that their polarization have a nonlinear transformation under the external electric field can be used for fabricate microwave tunable devices such as phase shifters, oscillators, filters and delay lines etc. As far as microwave tunable dielectric materials, barium strontium titanate(BST) and its family have been investigated intensively. Recently, Cross et al. found that lead strontium titanate (PST) ceramic has larger tunability and lower loss. It is favorable to be used in microwave tunable devices. Compared with BST materials, especially in thin films, PST has smaller ferroelectric critical size, lower crystallization temperature, only one phase transition and compatible with Si micro-electronics technology. Moreover, it is important to promote the development of the miniaturization and integration for the modern devices. At present there are only a few research on the PST materials, especially on the thin films, and the property of the thin film is far away to the expectation. Much work should be done for the improvement of PST thin film's performance.This thesis reviewed the development of the microwave tunable ferroelectric thin film materials, summarized the research methods for improve the film property, and introduced the principle and application of the microwave tunability in brief, showed a new way to prepare oriented PST thin films by sol-gel combining with rf (radio frequency) magnetron sputtering techniques.Oriented PT thin films were prepared on ITO glass substrate as a inducing layer by sol-gel. High (100) oriented PST thin films were successfully prepared on PT inducing layer by rf magnetron sputtering with pure perovskite structure. X-ray diffraction, Scanning electron microscope and impedance analyzer were used to investigate the crystallinity, structure, surface morphology and dielectric properties of the films.The PT inducing layer could provide nucleation sites for the PST thin films, decreased the nucleation barrier and improved the crystallinity of PST thin films. Under the same condition, the oriented PST thin films showed better crystalline and dielectric properties. Thethermal anneal process would influence on the properties of oriented PST thin films. As the anneal temperature increased, the crystallinity of films were improved and the the grain size increased, Contributing to the increase of Capacitance. When the anneal temperature was too high, the formation and nucleation speed of crystal would be too fast and the grain size would decrease, so the crystalline volume and Capacitance decreased. Under certain high temperature, the longer the anneal time was, the less crystalline volume the films were. The oriented PST thin films had larger relative change of crystallinity than the non-oriented one.The high sputtering power would improve the crystallinity of the oriented PST thin films due to more target particles deposited on the substrate and stack more densely. The capacitance and tunability increased with the better crystalline condition while the dielectric loss decreased.The thickness of inducing layer would also influence on the properties of PST thin films. As the thickness of PT increased, the crystallinity and tunability of PST thin films decreased. The crystallinity, tunability and figure of merit (FOM) of oriented PST thin films were all far more better than those of non-oriented PST thin films while the tunability improved by 1 time and FOM improved by 3 times. The largest tunability of 62.66% was obtained under 40V and the value might be further if applied a higher voltage.