Measurements of Hand D diffusion in Ti0 2 • using the isotope exchange technique described in the preceding paper. are reported. Use of this technique resulted in diffusion which was accurately described by Fick's law with a constant diffusion coefficient, as predicted theoretically. in sharp contrast to single ion diffusion, where dramatic departures from classical diffusion theory were observed. The measured diffusion coefficients for H were 1.8X 10-3 exp( -O.5geV/kT) and 3.8X 10-1 exp( -1.28eV/kT) cm 2 /sec for diffusion II and 1 to the c axis, respectively. Ionic conductivity measurements are reported. which agree well with the bulk diffusion measurements. and permitted us to extend the temperature range of the measurements for c -axis diffusion from 125 to 750"C, corresponding to a range of more than four orders of magnitude in D. The measured diffusion parameters were found to be essentially independent of sample purity. although it was observed that significant concentrations of lattice defects sharply inhibited H diffusion.
The electrical degradation of (Ba, Sr)TiO3 [BST] thin films as a function of the film thickness was investigated. BST thin films with various thickness were deposited on Pt/Ti/SiO2/Si substrates by in-situ RF magnetron sputtering. It was found that the electrical properties degraded markedly as the thickness of the films decreased. Electrical properties such as the leakage current and the dielectric constant are closely related to the surface morphology, in particular, the grain size of the films. The existence of an interfacial layer between the BST film and the Pt bottom electrode was confirmed by HRTEM. The interfacial layer appeared to have crystallinity different from both the BST thin film and the Pt bottom electrode which resulted in variation of the interfacial states between BST and Pt. As the thickness of the BST films decreased from 300 nm to 50 nm, the thickness of the interfacial layer increased from 9.5 nm to 11 nm. The dielectric constant of the interfacial layer calculated from its measured overall capacitance and thickness, confirmed by HRTEM, was about 30. This low-dielectric-constant interfacial layer has been shown to affect the electrical degradation of BST thin films with decreasing thickness.
Thin films of tantalum nitride have been deposited from remote plasma-assisted metal organic chemical vapor deposition (RP-MOCVD) using the reaction of pentakis-dimethyl-amino-tantalum (PDMATa) with different activated radicals. Microstructures of deposited films measured by X-ray diffraction (XRD) and transmission electron microscopy (TEM) depend on the deposition temperature and the type of radicals. At temperatures below 300°C, amorphous films are obtained which are independent of the reacting species. On the other hand, at higher deposition temperatures, (111)-preferred cubic TaN films are obtained when they react with ammonia plasma, while the reaction with hydrogen plasma produces amorphous films. All amorphous films obtained are recrystallized at an annealing temperature of 1000°C in an oxygen-containing (10%) ambient, showing (111) TaN, bcc Ta, and signals of orthorhombic Ta2O5. From detailed studies of film composition and chemical bonding in the obtained films, the impurity incorporation, especially carbon, is responsible for the dependence of film microstructures on different deposition conditions.
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