Investigation of sputtered ferroelectric thin films on silicon substrates

This dissertation discusses the deposition and characterization of ferroelectric Pb(Zr,Ti)O3 (PZT) films on Si substrates using conventional on-axis sputtering with various template layers and bottom electrodes with the goal of studying the feasibility of fabricating high quality PZT films in an economical manner for high density probe storage applications.; In this work, polycrystalline PZT films with controlled crystal orientation have been successfully fabricated on Si substrates with both Pt and LaNiO 3 (LNO) bottom electrodes. The large grain size and high angle grain boundaries associated with polycrystalline PZT films make it difficult for them to be applied as recording media for probe storage applications. Consequently, it was concluded that epitaxial PZT films with well controlled orientation and smooth surfaces would be more promising to make good probe storage media.; The integration of epitaxial oxides on Si substrates is a big challenge using sputtering. Epitaxial Pt/Ag/Si, Nb-SrTiO3/TiN/Si and LNO/STO/TiN/Si were selected as substrates for PZT deposition.; Epitaxial ferroelectric PZT(53/47) and PZT(20/80) thin films with (100) orientation and a pure perovskite phase were successfully grown on Si substrates using epitaxial Pt/Ag and LNO/STO/TiN by a rf sputtering process. The annealed PZT films displayed only (100)/(001) peaks with much stronger intensity than the textured polycrystalline films. The four-fold symmetry peaks in phi scan along the (110) plane indicated that PZT grew epitaxially on Si substrates with a cube-on-cube relationship and no relative rotation between layers. This good epitaxial relationship reveals that the nucleation process started from the interface between the PZT film and bottom electrodes and further confirmed the feasibility of producing epitaxial PZT films by post-deposition annealing after sputtering. The measured remanent polarization Pr and coercive field Ec of the PZT(20/80) thin films on Pt/Ag/Si were 26 muC/cm2 and 110 kV/cm.; The value of 26 muC/cm2 for Pr in the epitaxial PZT(20/80) films on Pt/Ag/Si is smaller than the theoretical Pr value of 83 muC/cm2 for PZT(20/80). This reduced polarization is believed to be caused by the mixture of a-domains and c-domains. It is believed that the stress generated from the different thermal expansion coefficients (TEC) between the films and substrates played an important role in forming a-domains instead of c-domains. TEC of PZT is 6-7x10-6/°C while TEC of Si is 3.5x10-6/°C. Si substrates therefore apply a tensile stress to the PZT films during the cooling process, because Si has a smaller TEC than the PZT films. The tensile stress caused a-domains (polar axis in plane) to form, which reduced the total remanent polarization value along the out-of-plane direction. This large fraction of a-domains would cause detrimental effects to the probe recording since the regions with a-domains would not be able to be switched with a perpendicular electrical field and information loss would therefore occur.; Using conventional on-axis sputtering, epitaxial perovskite oxide films such as STO and conductive LNO have also been achieved on Si with TiN as template layers. On the top of those well developed bottom electrodes and template layers, epitaxial PZT films with well-defined hysteresis loops and good crystal orientation have been obtained. Though the polarization is smaller than that from PZT films on single crystal STO substrates due to the presence of a-domains, this is the first time that epitaxial PZT films were integrated on Si substrates using Pt/Ag and LNO/STO/TiN heterostructures by sputtering. Though the microstructure and corresponding electrical properties of the epitaxial PZT films are not sufficiently good to be used as recording media for probe storage application, this work demonstrates an economical way to fabricate epitaxial ferroelectric PZT films on Si substrates which could be used in other applications such as piezoel...