Epitaxial Growth Of Bi₂Sr₂CaCu₂O_x/YSZ Films On Si Wafer By Pulse Laser Deposition

Fabricating high quality Bi₂Sr₂CaCu₂O_X (Bi2212) thin film on silicon wafer is a key step to using this superconductor in micro-electronics devices. Due to the structure mismatching and element diffusion between film and Si substrate during depositing and annealing processes, it is necessary to use buffer layer, such as Yttria-stabilized zirconia(YSZ), to avoid reaction and improve the superconducting properties. Therefore, our goal in this work is to develop a process to realize an epitaxial growth of Bi2212/YSZ composite films on Si (100) substrate by using pulse laser deposition( PLD ) technology.As a fact that the optimal process to deposit Bi2212 film or YSZ thin film is different, we divided our work into two steps: Firstly, we studied optimal process for YSZ thin film by modifying deposition temperature, laser energy and partial oxygen pressure; Secondly, we studied the optimal process for Bi2212 thin film and its epitaxial growth mechanism on YSZ/Si(100) substrate. Both YSZ target and Bi2212 target were fabricated with solid sintering method. All films were deposited by PLD and characterized by X-ray diffraction(XRD), and its surface and cross-section microstructure were observed by SEM and AFM.When YSZ thin films were deposited on Si(100) wafer, the orientation growth of (100) YSZ is not shown until the substrate temperature is higher than 550℃, and predominated at 650℃. We also found an orientation growth of (111)YSZ under low partial oxygen pressure( such as10^-4Pa), and change to (001) YSZ orientation growth at high oxygen pressure( such as 20Pa), and it can be due to the particle in the plume plasma were scattered by the increasing of oxygen density in the chamber. The higher laser energy can improve the kinetic energy of particles, which is good for the quality of YSZ thin film. As-grown YSZ/Si was annealed at 800℃for 3 hours, the orientation growth of the film didn't change, but the size and quality of thin films were improved remarkably. From SEM images, we can see that columnar crystals in YSZ film, which is correlative to island growth mode for the film.After then, we studied the optimal process to form Bi2212 thin film on Si(100) substrate. Firstly, we deposited Bi2212 thin films on different substrates, such as Si(100), Si(111), MgO(100) and YSZ/Si(100). The results showed that the Bi2201 phase was formed at 650℃, instead of Bi2212. However, (001) orientation growth of Bi2201 was observed in substrates except Si(111). Bi2201 phase mostly converted to Bi2212 phase when as-grown films annealed at 800℃for three hours. XRD results shown that the (001) peaks of Bi2212 phase were strong and sharp, and Bi2212 phase is almost epitaxial growth on YSZ/Si(100). Thin films had smooth surface and the interface between YSZ and Bi2212 is very clean, being observed by AFM and SEM. As a buffer layer between Si and Bi2212, YSZ film play an important role not only because it could avoid the reaction of them, but also its' columnar crystals could be excellent plates for the epitaxial growth of Bi2201(Bi2212) along Si(100) plane.