Loss of ZnO explains the improved microwave loss quality ( Q ) for Ba(Znl,3Ta2/3)03 ceramics which have been sintered at high temperatures or longer times. Ordering of Zn and Ta is complete in 60 h at 14OO0C, but crystallographic distortion and Q continue to increase up to 120 h. As ZnO volatilizes from the sample, Ba replaces Zn on the B sites and permits additional crystallographic distortion; meanwhile, barium tantalate phases also appear. Crystallographic compositional data are presented to confirm this interpretation.
The degradation (fatigue) of dielectric properties of ferroelectric Pb(ZrxTi1−x)O3 (PZT) and SrBi2Ta2O9 thin films during cycling was investigated. PZT and SrBi2Ta2O9 thin films were fabricated by metalorganic decomposition and pulsed laser deposition, respectively. Samples with electrodes of platinum (Pt) and ruthenium oxide (RuO2) were studied. The interfacial capacitance (if any) at the Pt/PZT, RuO2/PZT, and Pt/SrBi2Ta2O9 interfaces was determined from the thickness dependence of low-field dielectric permittivity (εr) measurements. It was observed that a low εr layer existed at the Pt/PZT interface but not at the RuO2/PZT and Pt/SrBi2Ta2O9 interfaces. In the case of Pt/PZT, the capacitance of this interfacial layer decreases with increasing fatigue while the εr of the bulk PZT film remains constant. This indicates that fatigue increases the interfacial layer thickness and/or decreases interfacial layer permittivity, but does not change the bulk properties. For the capacitors with RuO2/PZT/RuO2 and Pt/SrBi2Ta2O9/Pt structures, however, the εr does not change with ferroelectric film thickness or fatigue cycling. This implies no interfacial layer exists at the interfaces and which can be correlated to the observed nonfatigue effect. Additionally, the equivalent energy-band diagrams of these different capacitor structures were proposed to complement the proposed fatigue mechanism.
Si02 films deposited by the decomposition of tetraethoxysilane (TEOS) at high temperatures have superior insulating properties and excellent step coverage, but are not compatible with aluminum metallization. Earlier work on the deposition of SiOt from TEOS concentrated on the properties of the film and on the modeling of thickness uniformity, but no attempt was made to probe the decomposition chemistry. In the present work a three-step model is presented to explain the TEOS deposition chemistry. A useful deposition temperature is determined by the first step where an intermediate is formed in the gas phase. This activated species adsorbs on the surface and later decomposes into Si02. Equilibrium constants for the gas-phase intermediate formation and surface adsorption respectively are 1.38 X 10" exp[( -299.24 kJ/ mol)/RT] and 1.14 x lo4 exp[( -21.80 W/mol)/RT]. The rate constant for the surface decomposition of the intermediate is 1.29 X exp[( -12.26 kJ/mol)/RT]. This model successfully explains rate dependence on pressure and temperature. Approaches are suggested which would catalyze the formation of the activated species and thus lower the deposition temperature such that this process could he used instead of aluminum metallization. [
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