Synthesis, Structure and VLF Dielectric Permittivity of Hydrophobic, TMOS-Based Silica Aerogels

As cutting-edge semiconductor devices become smaller and more densely packed (i.e., ultra large-scale integration, ULSI), there is an increased risk of parasitic capacitance preventing proper device operation. There is consequently growing interest in the development of low-permittivity dielectric materials to serve as intermetal/interlayer coatings that would minimize this effect. Highly porous aerogels exhibit extremely low dielectric permittivity; silica-based aerogel films, in particular, are candidates for this application. The present report focuses on the synthesis, structure and dielectric permittivity of hydrophobic, tetramethyl orthosilicate (TMOS)-based silica aerogels prepared in disc-form. Using our 3D printed polymer sample holder with few metallic components, we are now able to determine the dielectric permittivity of highly porous, hydrophobic silica aerogels in the very low frequency (VLF) range, 10-27 kHz. Commercial systems that operate in the VLF range include circuits for biological signal processing, characterized by low amplitude and frequency, and circuits that operate in marine environments, where the useful frequency range is limited by acoustic signal deterioration. During impedance measurements, aerogel samples were confined in pure, dry oxygen atmosphere. Low mass density (10-250 mg/cm³) TMOS-based aerogel discs present structural characteristics and relative dielectric permittivity values in the VLF range that are not readily comparable with analogous data reported to date in the relevant literature.