Amorphous Alumina Barrier Coatings on Glass: MOCVD Process and Hydrothermal Aging

Abstract

OATAO is an open access repository that collects the work of Toulouse researchers and makes it freely available over the web where possible. This is an author-deposited version published in : http://oatao.univ-toulouse.fr/ Eprints ID : 15772 [ 9 ] radio frequency magnetron sputtering, [ 2 ] atomic layer deposition, [ 10 ] sol-gel, [ 5 ] and metalorganic chemical vapor deposition (MOCVD). [ 7,[11][12][13] CVD is one of the most attractive techniques for the time effi cient deposition of such coatings on complexin-shape geometries with conformal coverage, i.e., uniform thickness along the surface. Composition, stoichiometry, crystallinity, and microstructure of the material can be adjusted by fi ne tuning of the MOCVD experimental parameters such as reactor design, precursor selection, reactive atmosphere, deposition temperature, and pressure. The MOCVD of alumina from vaporized aluminum tri-isopropoxide (ATI) is very well documented. [ 7,8,[11][12][13][14][15][16] ATI yields amorphous and stoichiometric alumina coatings with a smooth and dense microstructure at 5 Torr in the temperature range 420 to 650 °C. [ 7,8,14,15 ] Higher process temperatures lead to the deposition of nanocrystallized γ -Al 2 O 3 [ 15 ] or to the homogeneous decomposition of ATI, which generates a different microstructure. [ 11 ] The ATI molecule is well described in the literature.[ 17 ] It is sensitive to water vapor and thus it is subjected to ageing upon exposure to ambient atmosphere, which results in its partial or total hydrolysis in nonvolatile compounds, Al(O i Pr) 3− n (OH) n ( n = 1, 2) and Al(OH) 3 , respectively. [ 12,17 ] The precursor is usually melted, maintained in supercooled state, and vaporized with a bubbler.Despite the simplicity and the cost effectiveness of this solution, the use of ATI in the supercooled state has two drawbacks. First, maintaining ATI at the vaporization temperature for a long-period impacts the stability of the molecule and subsequently the coating quality. [ 12 ] Second, it is diffi cult to know exactly the mass fl ow rate of the generated reactive gas. Such poorly controlled transport conditions lead to nonreproducible processes, especially for the present case when low activation energy prevails in the entire temperature range of interest, de facto resulting in mass transport limited process. The direct liquid injection (DLI) technology overcomes these drawbacks with the controlled vaporization of the solution made of ATI dissolved in a carrier solvent. [ 18 ] The DLI of ATI is insuffi ciently documented in the literature. Song et al. [ 19 ] and Krumdieck et al. [ 13 ] implemented the technique in a pulsedpressure MOCVD process. The authors used a solution of ATI in n -octane and in dry toluene, respectively. Coatings obtained

Atomic scale structure of amorphous aluminum oxyhydroxide, oxide and oxycarbide films probed by very high field27Al nuclear magnetic resonance

“…17 In contrast, the films obtained from DLI ATI show a columnar growth of agglomerated nodules. 20 This microstructure contrasts strikingly with the one observed for films grown using evaporated ATI suggesting that the solvent (cyclohexane) used in DLI plays an important role in the nucleation and growth of the film. Secondly, EPMA and XPS analyses showed that the O/Al ratio is generally different from the one of stoichiometric alumina (O/Al = 1.5) over a wide range of temperature.…”

“…Deposition experiments were performed in a custom-made, horizontal, hot-wall CVD reactor described in previous works. [17][18][19][20] Films were grown on either 50 mm (University wafer) or 100 mm thick (Sil'tronix), (100) oriented silicon wafers. Using thinner Si substrates increases the amount of alumina material in the NMR probe, which reduces the measurement time and/or increases the signal to noise ratio.…”

“…In view of their injection in the process chamber, both ATI and DMAI are dissolved in anhydrous cyclohexane. 19,20,24 For DMAI, the O/Al ratio is equal to 1 (O/Al = 3 for ATI) and for this reason an additional oxygen source (H 2 O or O 2 ) is required for the CVD of alumina from this precursor (O/Al = 1.5 in alumina). 17,18 The experimental protocols used for each process are presented in detail in the corresponding references and the process conditions are summarized in Table 1.…”

“…14 Alternatively to evaporated ATI, another CVD process to synthesize amorphous alumina films was investigated by using the direct liquid injection (DLI) technology with ATI or dimethylaluminum isopropoxide (DMAI). [17][18][19][20] DMAI is an alumina CVD precursor which has several advantages over ATI such as a significantly higher vapor pressure; it is liquid at room temperature, has a long shelf-life and allows processing of alumina films at T d as low as 150 1C. 17,18,21 Scanning electron microscopy (SEM) and elemental analyses (electron probe micro analysis, EPMA and X-ray photoelectron spectroscopy, XPS) of the amorphous alumina films revealed different microstructures and chemical compositions depending on both the nature of the precursor and the deposition temperature.…”

Fluidized bed chemical vapor deposition of copper nanoparticles on multi-walled carbon nanotubes

“…To overcome the limitation of the low precursor volatility, a more efficient delivery system like Direct Liquid Injection (DLI) could be used [49], in order to work with much higher inlet precursor molar fractions. Thanks to its versatility, the FBCVD process allows depositing various metals or metalloids on MWCNTs or on other porous or nonporous powders, this opening the way for the industrial production of innovative multi-functional materials in the fields of catalysis, Li-ion battery, and composite materials.…”