Orientation Control And Ferroelectric Integration Of SrRuO₃ Thin Films

SrRuO₃（SRO） is unique in that it is a 4d transition metal oxide that exhibits ferromagnetism and metallic conductivity. Due to its large vertical remanent magnetization, superior conductivity, good chemical stability and low lattice mismatch with common ferroelectric materials（e.g. Pb（Zr,Ti）O₃ and BaTiO₃）, SRO has gained much attention for multilayer device applications including magnetic tunnel junction（MTJ）, magnetic storage, ferroelectric random access memories（FeRAM）, and Micro Electro Mechanical Systems（MEMS）. At present, most investigation of SRO films are focus on the epitaxial films grown on single crystalline oxide substrates, Si-based oriented SRO films especially its magnetic behavior and electrical transport properties are less investigated. In this thesis, based on the problems mentioned above, growth and properties of SRO films have been studied. The main results and innovative achievement are listed as follows:（1） SrRuO₃（SRO） thin films were grown on SiO₂/Si substrates with different thickness of LaNiO₃（LNO） seed layers by RF magnetron sputtering. Effects of LNO thickness on the grain orientation, surface morphology, magnetic behavior and electrical transport properties of SRO films were investigated. The orientation of SRO films transformed from（110） to（001） and the residual stress was released gradually with increasing the thickness. SRO films with higher orientation grown on LNO exhibited more flat surface, higher saturation magnetization, and lower coercive field. The magnetic anisotropy was enhanced on thicker LNO due to the different states of residual stress. In addition, the temperature dependence of resistivity was promoted by the microstructural disorder.（110）-oriented SRO monolayer electrode and（001）-oriented SRO/LNO₃00 bilayer electrode own low room temperature sheet resistance of 0.38 Ω/□ and 0.26 Ω/□, respectively. The results indicate that the controllable SRO films can be used as not only good bottom electrodes but also promising templates to control the crystallographic orientations of various other perovskite-based functional materials.（2） A series of SrRuO₃（SRO） thin films with different orientations were grown on SrTiO₃（STO） and Si substrates by RF magnetron sputtering. The type of residual stress of the deposited films were analyzed. The influence of residual stress on magnetic behavior and electrical transport properties were also systematically investigated. X-ray diffraction results show that Si-based SRO films are under tensile strain with uniaxially oriented grains, while the STO-based films are compressively strained with epitaxial structure. Curie temperature TC is improved for（001） orineted SRO films, but is reduced for the（110） oriented films, duo to the compressive stress. In addition, the microstructure disorder is enhanced, and the temperature dependence of resistivity is suppressed by the tensile stress, accompanied by the shifts of the temperature of metal-insulator transition to the higher temperature.（3） Randomly and（001）/（100） oriented PZT films were fabricated on（110）-SRO and（001）-SRO bottom electrodes by RF magnetron sputtering, respectively. The influence of different oriented SRO electrodes on the electrical properties of PZT films were investigated. It is found that both the films showed a stable frequency dependence of dielectric permittivity（?r） and loss tangent（tanδ） in the range of 100 Hz – 1 MHz. the textured PZT films possesses higher ?r of 682 and lower tanδ of 0.06 at 1 kHz. An enhanced ferroelectricity was also obtained in the（001）/（100）-oriented PZT films, with a remnant polarization of 42 μC/cm2 at the applied field of 925 kV/cm and a fatigue-free behavior up to 107 switching cycles.