Incorporation of Linear Spacer Molecules in Vapor-Deposited Silicone Polymer Thin Films

Poly(trivinyltrimethylcyclotrisiloxane)or polyV(3)D(3) is a promising insulating thin film known for its potential application in neural probe fabrication. However, its time-consuming synthesis rate renders it impractical by manufacturing standards. Previously, the growth mechanism Of polyV(3)D(3) was shown to be affected by significant steric barriers. This article describes the synthesis of a copolymer Of polyV(3)D(3) via initiated chemical vapor deposition (iCVD) using V3D3 as the monomer, hexavinyldisiloxane (HVDS) as a spacer, and tert-butyl peroxide (TBP) as the initiator to obtain nearly a 4-fold increase in deposition rate. The film formation kinetics is limited by the adsorption of the reactive species on the surface of the substrate with an activation energy of -41.5 kJ/mol with respect to substrate temperature. The films deposited are insoluble in polar and nonpolar solvents due to their extremely cross-linked structure. They have excellent adhesion to silicon substrates, and their adhesion properties are retained after soaking in a variety of solvents. Spectroscopic evidence shows that the films do not vary in structure after boiling in DI water for 1 h, illustrating hydrolytic stability. PolyV(3)D(3)-HVDS has a bulk resistivity of (5.6 +/- 1) x 10(14) Omega.cm, which is comparable to that of parylene-C, the insulating thin film currently used in neuroprosthetic devices.