Pulsed-PECVD Films from Hexamethylcyclotrisiloxane for Use as Insulating Biomaterials

Abstract

Thin films produced by plasma-enhanced chemical vapor deposition (PECVD) have potential application as conformal coatings on implantable devices with complex topologies and small dimensions. Coatings on such devices need to be biocompatible, insulating, and flexible enough to minimize static forces on the surrounding tissue. In this study, we describe the use of pulsed-PECVD to deposit thin films from hexamethylcyclotrisiloxane (D3). Pulsed-PECVD is a method in which plasma excitation is modulated to favor deposition from neutral and radical species. Thin, conformal coatings were demonstrated on nonplanar substrates suitable for implantation, such as copper wires and neural probes. Coatings were resistant to prolonged immersion in warm saline solution, and wire coatings produced by pulsed-PECVD showed more flexibility than analogous coatings deposited by continuous-wave (CW) excitation. Using Fourier transform infrared spectroscopy, it was demonstrated that the mode of plasma excitation is important in determining film structure. Both CW and pulsed-PECVD showed evidence of cross-linking via ternary and quaternary silicon atoms bonded to more than two oxygen atoms. Methylene groups were observed only in CW films, and may constitute part of a carbon cross-linking unit of the form Si(CH2) n Si, where n ≥ 1. Methylene was not detectable in the pulsed-PECVD films, suggesting that formation of carbon cross-links requires a longer plasma decomposition period. The presence of two distinct cross-linking structures in CW films leads to a highly networked structure and results in brittle coatings on thin wires. A higher proportion of terminal methyl groups was also observed in CW films, suggesting that pulsed-PECVD films may retain more precursor ring structure than CW films.

Polarized raman spectroscopy for determining the orientation of di‐d‐phenylalanine molecules in a nanotube

“…Deposition was carried out under low vacuum conditions, with low chamber pressure (0.03 Torr), low argon flow rate (99.99% purity, flow rate of 10 cm 3 /min), and low radio frequency power (30 W) . The RF power was pulsed with frequency ranging between 100 to 1000 Hz and duty cycles ranging from 25% to 100%, because previous studies have reported that using a low power pulsed plasma helps the activation as well as the retention of chemical activity of the deposited molecule . The morphology of the PECVD deposited di‐ d ‐phenylalanine nanotubes are shown in Fig.…”

Low pressure plasma modifications for the generation of hydrophobic coatings for biomaterials applications

“…Although methyl abstraction was considered to be the key step in “continuous wave” (as opposed to pulsed) ppt for monomers such as HMDSO and HMDSN, the pulsed ppt of hexamethylcyclotrisiloxane showed complete absence of methylene groups in the resultant pps . The hexamethylcyclotrisiloxane pp incorporated Si(CH 3 ) 2 elements as part of the growing pp network during pulsed polymerization . Hence, it is important to also consider the effect of the molecular structure of the monomer on the final pp.…”

Initiated PECVD of Organosilicon Coatings: A New Strategy to Enhance Monomer Structure Retention

“…Pulsing a plasma discharge may induce alterations of the discharge chemistry, which depend on the time the discharge is active, t ON , the time it is unlit, t OFF , and the duty cycle DC = t ON /( t OFF + t ON ), where ( t ON + t OFF ) is the period. A film deposited by pulsed plasma can have significant different properties than one deposited by continuous plasma as largely demonstrated in the literature 16, 17. In PECVD processes with high fragmentation regimes, during the ON‐time the polymer growth is fast and the film is subject to positive ion bombardment, UV‐radiation and to the interactions with many unstable species and fragments.…”