| With the development of science and technology,the degree of integration and miniaturization of devices is getting higher and higher,and more and more people are paying attention to functional oxide films.Compared with traditional bulk materials,film materials have richer physical properties and broad application prospects.The properties of the film itself are critical to the reliability of the device,so it is also important to study the physical and chemical properties of the film itself.As a kind of functional oxide film,antiferroelectric film has many applications such as storage,energy storage,refrigeration,and strain braking.More and more people have begun to study it.Pb Zr O3 as a prototype material of antiferroelectric materials has excellent antiferroelectric properties.Therefore,more and more people have begun to study the structural phase transition of Pb Zr O3 film itself under many factors such as electric field,strain,temperature,thickness and so on.Previous research work has shown that as the thickness of the Pb Zr O3 film decreases,there will be a transition from the antiferroelectric phase to the ferroelectric phase.There are still divergent opinions on the reasons for this size effect.Since the energy difference between the Pb Zr O3antiferroelectric phase and the ferroelectric phase is very small,the cause of this size effect may not be unique.In this thesis,the optimal growth parameters of Pb Zr O3 film on(001)-oriented single crystal Sr Ti O3 substrate are obtained through the optimization of system process parameters.The root mean square roughness of Pb Zr O3 film grown under this parameter is below 300 pm.Two sets of Pb Zr O3 thin films with a thickness gradient were prepared using the best parameters obtained,one of which was directly grown on(001)-oriented single crystal Sr Ti O3 substrate;the other was grown indirectly with20 nm thick Sr Ru O3 thin film as bottom electrode on(001)oriented single crystal Sr Ti O3 substrate.The effect of bottomed electrodes on the crystal structure of Pb Zr O3thin films with different thicknesses was studied through two sets of comparisons;a series of electrical performance characterizations were performed on a set of bottomed electrodes to study the effects of strain and electrical boundary conditions on the structure of Pb Zr O3 thin films at different thicknesses.In the case of Sr Ru O3film as the bottom electrode,the Pb Zr O3 film changes its antiferroelectricity to ferroelectricity as the thickness decreases.Through analysis,it is found that the Pb Zr O3 film grown on the(001)-oriented single crystal Sr Ti O3 substrate has two different orientation domain structures(120)and(002);while the Pb Zr O3 film is grown indirectly with a 20 nm thick Sr Ru O3 film as the bottom electrode On the(001)oriented single crystal Sr Ti O3 substrate,there is only(120)one oriented domain structure.This is due to the different lattice mismatch of Pb Zr O3 films when there is no bottom electrode,which results in a lower energy when the(120)orientation has a Sr Ru O3 bottom electrode.The bottom-less electrode sample is completely relaxed at 75 nm,and is orthogonal to the bulk material;it is also relaxed at 12 nm.The sample with bottom electrode still has compressive stress in the plane at 85 nm,but there is also a quarter-order Bragg diffraction peak,so it is an orthogonal antiferroelectric phase.Because the film peak position of the bottom electrode sample basically does not move in the thickness range of 17-85 nm,and the out-of-plane lattice parameters of the antiferroelectric orthogonal phase and the ferroelectric rhombohedral phase are very close,the?-2?scan of the Pb Zr O3 film cannot distinguish whether there is phase transition as the film thickness decreases;when the film thickness is thinner,the peak intensity of the film is weak,and the peak position is difficult to distinguish.Subsequently,through the electrical characterization and analysis of Pb Zr O3films of different thicknesses grown indirectly on(001)-oriented single crystal Sr Ti O3substrates with a 20 nm thick Sr Ru O3 film as the bottom electrode,it was found that as the thickness of the Pb Zr O3 film decreases,it gradually changes from anti-iron.The electric phase is transformed into a ferroelectric phase.Therefore,when there is a bottom electrode,as the thickness of the film decreases,an anti-ferroelectric orthogonal phase to a ferroelectric phase transition occurs inside.Due to the small epitaxial strain,it can be concluded that the size effect of the Pb Zr O3 film is mainly due to the bottom electrode affecting its electrical boundary conditions and thus changing the crystal structure at the interface. |
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