Fabrication And Characterization Of Ba-x Sr_1-x TiO₃ And CeO₂ Thin Film

Epitaxial CeO₂ thin films, 10⁴0 nm thick, were deposited on Si(111) substrates by the pulsed laser deposition method. The metal-oxide-semiconductor (MOS) structures were further fabricated to evaluate the interface and dielectric properties of CeO₂ films. The results show that the C-V characteristics can be greatly affected by the interface charges. The epitaxial CeO₂ thin films, which are deposited by a two-step process, have larger dieleltric constant and lower interface trap density. The permittivity calculated from the EOT-T_phys characteristics curve is about 37, and the interface trap density is about 10¹² order of magnitude according to the Hill-Coleman method.Ba_0.6Sr_0.4TiO₃ (BST) thin film was deposited on CeO₂/Si(111) substrate by the pulsed laser deposition method and CeO₂ buffer layer was used to improve the crystal quality of the films. The impact of temperature under different oxygen pressure on the microstructure of BST films is investigated. It is found that the BST are highly preferred at 750℃and the deposition pressure of 1.0 Pa. The metal-ferroelectric-insulator-semiconductor(MFIS) structures were further fabricated to evaluate the dielectric properties of the films, the memory window is 0.8 V at 5 V bias voltage. The leakage current density measured at the voltage of 10 V is 8.5×10^-7 A/cm².Pt/La_0.5Sr_0.5CoO₃/BST/La_0.5Sr_0.5CoO₃/CeO₂/Si (Pt/LSCO/BST/LSCO/CeO₂/Si) capacitors were fabricated on Si(111) substrates using RF magnetron sputtering and pulsed laser deposition methods. It is found that BST thin films are polycrystalline, and the maximum dielectric constant and tunability of BST thin films are 493 and 22%, respectively. The Leakage current density of the LSCO/BST/LSCO capacitor is 8.7×10^-6 A/cm² at the voltage of 5 V.Pt/Ni-Ti/Ba_0.6Sr_0.4TiO₃/Ni-Ti/Pt and Pt/Ba_0.6Sr_0.4TiO₃/Pt capacitors were fabricated on Pt/TiO₂/SiO₂/Si(001) substrates using RF magnetron sputtering and pulsed laser deposition methods. It is found that the microstructure of BST thin film did not change obviously after introducing the amorphous Ni-Ti barrier layer. However, the barrier layer effectively inhibits the diffusion between the Pt electrode and BST thin film, reduces the thickness of dead layer, and significantly increases the dielectric constant of BST thin films. Compared with the Pt/Ni-Ti/BST/Ni-Ti/Pt and the Pt/BST/Pt capacitors, the former have a smaller dielectric loss and lower leakage current density.