Relva C. Buchanan

Preparation and stoichiometry effects on microstructure and properties of high purity BaTio3

Effects of stoichiometry, precursor origin and powder synthesis method on sintered microstructure and dielectric properties of commercial high purity BaTiO3 were examined, with a view to potential interchangeability. Powders used were prepared by conventional calcination, by precipitation from oxalate precursors and by hydrothermal synthesis. Stoichiometric (Ba:Ti) ratios were in the range 0.987 to 1.002. Characterization by SEM, x-ray diffraction, BET surface area and particle size analysis revealed significant differences, particularly in agglomerate structure, resulting in different microstructural development. Stoichiometric effects on microstructure were also significant, if predictable. However, the combined effects of agglomerate structure and stoichiometry on measured dielectric properties could not be predicted, hence interchangeability of powders could not be achieved.

Oxide thin films for nanometer scale electron beam lithography

The exposure response of high resolution oxide resist materials has been examined under high intensity irradiation conditions ({similar to}1{times}10{sup 5} A/cm{sup 2}) to determine the relationships among film characteristics, exposure requirements, and ultimate resolution, and to explore further the processes responsible for ablative exposure. Amorphous films of Al{sub 2}O{sub 3}, Y{sub 2}O{sub 3}, Sc{sub 2}O{sub 3}, 3Al{sub 2}O{sub 3}{center dot}2SiO{sub 2}, and MgO{center dot}Al{sub 2}O{sub 3} were deposited by rf sputtering onto substrates cooled to {minus}196 {degree}C and found to require an exposure dose of approximately 5{times}10{sup 3} C/cm{sup 2} to complete exposure. Amorphous film structure was found to be necessary to achieve rapid removal of material during exposure. Material properties also found to influence irradiation response and help guide the selection of new materials included ionic character, heat of formation, and melting point. Film thickness was found to strongly influence both exposure requirements and resolution, an optimum thickness occurring at approximately 90 nm in amorphous Al{sub 2}O{sub 3}. The dose requirement in 90 nm thick amorphous Al{sub 2}O{sub 3} was determined to be 2.5{times}10{sup 3} C/cm{sup 2}, which is two to three orders of magnitude lower than that of oxide films produced by other techniques, and the resolution ofmorexa0» the rf sputtered oxide films allowed the production of 5.0 nm holes on 8.1 nm centers. A dedicated STEM was used for exposure studies as well as imaging, microdiffraction analysis, and monitoring of the transmitted beam current, and allowed a qualitative model of the exposure process in rf sputtered oxide resists to be developed.«xa0less

Influence of grain boundary, defect and internal stress states on properties of ferroelectric materials

Abstract Performance characteristics in ferroelectric based components, sensors and thin films for memory and storage applications are significantly influenced by aging instability in these perovskite materials. The aging changes can be attributed both to dc electrochemical effects, where migration of ionic charges lead to degradation in permittivity, loss and resistance, and to changes in domain structure and mobility. This latter reflects the presence within the microstructure of defect states, diffuse grain boundary structures and internal stresses. Aging in these materials is also dependent on microstructure, impurities, dopants and stoichiometry, as well as on ambient temperature and applied dc field stresses. Significant improvements in aging and performance characteristics have been achieved with selected dopant additions to BaTiO3, such as ZrO2, which control grain morphology, resulting in structural modifications and decreased domain mobility. Permittivity has been found to be highly dependent on...

Characteristics of oxide thin films from carboxylate precursors

Oxide thin films on Si substrates were prepared from carboxylate precursors by the reaction of the metal nitrates and ammonium trimethylacetate. Precursor salts were characterized with respect to purity, structure, thermal pyrolysis, and phase development during calcination. A solvent system, based on carboxylic acid/amine mixture, was developed to dissolve the synthesized precursors, resulting in increased solubility, viscosity, and stability. Smooth, fine-grained ZrO{sub 2}, Y{sub 2}O{sub 3}, and YSZ films were obtained on Si wafers by spin-coating and subsequent heat treatment above 500 {degree}C. Films heat treated below 700 {degree}C were generally adherent, amorphous, or microcrystalline, while YSZ and ZrO{sub 2} showed (111) preferred orientation above 700 {degree}C. These oxide films show promise as protective or buffer layers on Si wafers.

Metal Oxide Films from Carboxylate Precursors

Zirconium oxide and Ba{sub 2}YCu{sub 3}O(7-X) metal oxide films were prepared from carboxylate precursors. The zirconia films were prepared from Zirconium octoate and the Ba-Y-Cu-O compound synthesized from a mixture of the metal neodecanoates. Dense, adherent ZrO{sub 2} films were obtained on silicon. Dense, superconducting Ba-Y-Cu-O films were also fabricated utilizing the octoate-derived ZrO{sub 2} as a bonding surface and diffusion buffer. Preparation methods for thin oxide films using metal carboxylate precursors have been demonstrated. Favorable superconducting properties were obtained with the (1,2,3) film deposited on the ZrO{sub 2}/Si films, showing ZrO{sub 2} to an effective diffusion barrier.

Phase transformation and preferred orientation in carboxylate derived ZrO 2 thin films on silicon substates

Phase transformation and preferred orientation in ZrO 2 thin films, deposited on Si(111) and Si(100) substrates, and prepared by heat treatment from carboxylate solution precursors were investigated. The deposited films were amorphous below 450 °C, transforming gradually to the tetragonal and monoclinic phases on heating. The monoclinic phase developed from the tetragonal phase displacively, and exhibited a strong (111) preferred orientation at temperature as low as 550 °C. The degree of preferred orientation and the tetragonal-to-monoclinic phase transformation were controlled by heating rate, soak temperature, and time. Interfacial diffusion into the film from the Si substrate was negligible at 700 °C and became significant only at 900 °C, but for films thicker than 0.5 μm, overall preferred orientation exceeded 90%.

Hole pattern formation in unfired ceramic sheets by pulsed Nd:YAG laser

Single shot pulses from a Nd:YAG laser have been used to generate different sized holes and patterns in unfired ceramic sheets for electronic packaging applications. The single shot laser pulses were targeted using a computer controlled deflection system and a programmed pattern. With changes in pulse energy level and profile, the laser beam was also used to sinter line patterns in deposited thin and thick films. The surface radial temperature profile resulting from the laser pulse interaction was also directly mapped using a lacquer thermocoat. Effects of the laser pulse energy and beam spot size on laser/ceramic interactions, morphology, and structure of the drilled holes before and after sintering were examined by SEM. High quality hole patterns (of ∼100 μ m hole size) were produced in unfired 100 μ m thick ceramic sheets up to 100 μ m thick using single shot of laser irradiation with 8 mJ pulse energy and 18 nsec pulse duration.

Cavitation in Unfired Ceramic Sheets by Pulsed Nd:YAG Laser

Single shot pulses from a Nd:YAG laser were used to generate different sized holes and patterns in tape-cast ceramic sheets for electronic packaging applications. The ceramic sheets were based on formulations in the BaTiO 3 and MgO-Al 2 O 3 -SiO 2 systems. The single shot laser pulses were targeted using a computer controlled mirror deflection system and a programmed (cavitation) pattern which could readily be modified. Morphology and structure of the drilled holes before and after sintering were examined by SEM. The surface radial temperature profile resulting from the laser pulse was directly mapped using a lacquer thermocoat. Effects of the laser pulse energy and beam spot size on laser/ceramic interactions and cavitation process were also explored.

Investigation of Processing Parameters on Stability of (SOG) Files on Patterned Si Wafers

Polymeric sols of SiO 2 or siloxane polymers in n-propanol were investigated for use as dielectric and planarization layers on patterned silicon wafers for device application. Spin coating of the sol (SOG) resulted in rapid gelation through solvent evaporation but cracking often occurred on heating. This study examined the influence of SOG composition, deposition process and heating rate on film planarization and cracking. Planarization was found to be enhanced by layer thickness, but cracking stability was reduced. Sequential drying of the applied SOG layers and use of trlethano-lamine as a complexing base was found to significantly reduce cracking tendency in the films.

Effect of core shell morphology on dielectric properties of Zr doped BaTiO/sub 3/

The core-shell grains and lattice structure in Zr-modified BaTiO/sub 3/ were characterized. Through TEM (transmission electron microscopy), CBED (convergent-beam electron diffraction), and EDS (dispersive X-ray spectroscopy) techniques, the shells were identified as diffuse regions of pseudocubic structure surrounding a tetragonal BaTiO/sub 3/ core. Grain morphology and developed internal stresses in BaTiO/sub 3/-based high dielectric materials are shown to be a dominant factor in the development and stability of the high dielectric properties. Core-shell grains were formed in BaTiO/sub 3/ with ZrO/sub 2/ doping, upon sintering in the range 1300 degrees C-1320 degrees C. A diffused boundary phase led to high internal stresses, suppression of T/sub c/, a distribution of Curie points, and a flattened permittivity peak. The internal stress was found to be an accurate basis for estimating the permittivity response to temperature. The stability of these highly stressed samples was also found to be improved as the concentration of core-shell grains increased. Under controlled processing parameters, therefore, significantly enhanced dielectric properties can be achieved.<<ETX>>