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

Poly (trivinyl-trimethyl-cyclotrisiloxane) 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 for 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 V(3)D(3) as the monomer, hexavinyl disiloxane (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 non polar solvents due to their extremely crosslinked 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 hour, illustrating hydrolytic stability. PolyV(3)D(3)-HVDS has a bulk resistivity of 5.6 (±1) × 10(14) Ω-cm, which is comparable to that of parylene-C; the insulating thin film currently used in neuroprosthetic devices.