Properties of Films Prepared from Low Surface Area/Density Alumina-Silica
- PDF / 338,828 Bytes
- 5 Pages / 420.48 x 639 pts Page_size
- 26 Downloads / 173 Views
PROPERTIES OF FILMS PREPARED FROM LOW SURFACE AREA/DENSITY ALUMINA-SILICA S.L. Hietala, D.M. Smith, UNM/NSF CENTER FOR MICRO-ENGINEERED CERAMICS, University of New Mexico; V.M. Hietala, G.C. Frye, A.J. Hurd, and C.J. Brinker, Sandia National Laboratories, Albuquerque, NM
ABSTRACT A sol-gel method was used to prepare bulk, closed pore, amorphous alumina-silica. Films prepared from this 47wt% A12 03-SIO2 composition were examined by SAW, ellipsometry and electrical measurements. The films were found to have a surface area of 1.1 cm 2/cm 2 , a refractive index of 1.44 at 633 nrm, and a relative permittivity of 6.2 at 200 KHz. These properties indicate potential applications as hermetic seals, barrier coatings, dielectric layers for capacitors and passivation coatings for electronic circuits.
INTRODUCTION An amorphous alumina-silica material prepared via sol-gel routes was found to have an anomalously low surface area and density in a composition of approximately 47 wt% alumina [1]. From various techniques, it was determined that these properties were due to closed porosity in the material [2]. If closed porosity can be maintained in the films, they would be ideally suited for hermetic, thermal, and chemical barriers. The large amount of porosity also suggests it as a candidate for reasonably low relative permittivity ceramic coatings for electronic applications.
EXPERIMENTAL The 47wt% alumina-silica sol was prepared using alkoxide precursors. Ethanol was added to TEOS in a round bottom flask. A solution of ethanol and HC1 (molar ratios 1 EtOH: 1 conc. HCI: 0.8 TEOS) was added to the flask, then an appropriate amount of aluminum tri-sec butoxide (ASB) was added. This was allowed to react (with slight agitation) for several minutes, then diluted with ethanol, and refluxed at 353K overnight. The gel was formed by adding water (molar ratios 100 H2 0:Si) to the sol and allowing the gel to start forming. Films were prepared by spin coating at 2000 rpm. Dynamic light scattering was performed on a series of gelling mixtures using a Wyatt spectrometer equipped with the autocorrelation option. The two components of each sample were
filtered through a 0.2 ptm filter into a clean, dust-free scintillation vial where they were gently
mixed then place in the spectrometer. Temperature was controlled to 37.0 ± 0.5 OC. Focused
HeNe light (633 rim) was scattered at a fixed angle of 920 and collected by a SelFoc optical fiber, which fed the scattered light to a Hamamatsu photomultiplier tube. The intensity autocorrelation function was obtained by feeding the photocurrent to a Langley-Ford 1096 digital
autocorrelator via a preamplifier. The data were taken at 20 minute intervals continually from the
time of mixing until the gel time, which was (crudely) determined by observing an aliquot. To characterize porous films using surface acoustic wave (SAW) devices, the solution was cast onto a quartz substrate then placed in a brass test case with a stainless steel lid for gas inlet and outlet. The devices were cooled to liquid N2 tempe
Data Loading...
