(236b) Patterning Polymer and Metal Microstructures On Curved Substrates Via Initiated Chemical Vapor Deposition (iCVD)

Fabrication of polymer microstructures is an essential step in the production of microelectronic, optical, and biomedical devices.  The ability to pattern features on curved substrates is of particular interest, as it enables the fabrication of devices with unique or improved properties. A patterning technique for curved substrates has been developed using Initiated Chemical Vapor Deposition (iCVD).  In this process, vapor-phase monomer(s) and thermally-labile initiator pass through an array of heated filaments.  The initiator decomposes into radicals; these radicals and the monomer(s) adsorb onto a cooled substrate, and simultaneous free radical polymerization and thin film formation occur. Since surface tension and de-wetting effects are absent, iCVD thin films conform to the geometry of the underlying substrate. Additionally, the benign reaction conditions inherent to this low-energy process allow for complete retention of polymer functionality.

 A thin film of poly(4-vinylpyridine) (P4VP) is deposited on substrates using iCVD.  After deposition, the photosensitivity of the film is enhanced via functionalization with 10,12-tricosadiynoic acid (TDA). The functionalized film is exposed at 254 nm, inducing 1,4 addition photopolymerization of the TDA.  Unexposed regions remain soluble and are removed upon developing.  Incorporation and polymerization of TDA have been verified using FTIR, Raman, and UV-visible spectroscopy.  Functionalization improves the UV sensitivity of the film by a factor of 10, and the resulting value (71 ± 10 mJ/cm²) is comparable to that of commercial products.  Processing time is on the order of 1 h and multiple substrates can be prepared simultaneously.  Thicknesses of patterned polymer films range from 40-200 nm, and features on the order of 1 μm have been obtained.  Polymer microstructures have been patterned on glass rods with diameters of 2 to 6 mm, then used as masks to pattern metal features. The vapor-phase processing used in this method also facilitates the fabrication of bifunctional polymeric surfaces; since no solvents are used, underlying polymer layers cannot be dissolved as new layers are formed.  Surfaces consisting of alternating regions of poly(1H,1H,2H,2H-perfluorodecyl acrylate) and functionalized P4VP have been patterned; successful fabrication was confirmed by comparing the static contact angles of water droplets measured in each region of the patterned substrate.