Direct UV-Written Fluorinated Materials For Optical Waveguides

With the rapid development of microelectronics, optoelectronics, computing and communications, human society is gradually entering into an information age. Polymer optical waveguides have attracted considerable attention for use in economical and practical optoelectronic devices and as interconnections in optical communication systems due to it is easier to fabricate these waveguides by spin casting than inorganic material waveguides. Direct-write UV lithography is one of the candidates of photolithography technologies for fabricating micropatterns, even nanoscale structures.8,9 Therefore, it is desirable to have a deep-UV photoresist that can be used both as the core and the grating structures. The theory and development of these types of organic polymer materials for optical waveguide have been reviewed in chapter 1. And two things about polymer waveguide materials have been introduced respectively. One is the special property of polymer waveguide materials; the other is the type of the polymer for optical waveguide.In this dissertation, we can define three general approaches to achieving novel and high performance polymer fluorinated photoresists for optical waveguide。In chapter 3, a fluorinated bis-phenol-A novolac resin (FSU-8) for optical waveguide was synthesized based on 4, 4-(hexafluoro-isopropylidene)diphenol, epoxy chloropropane and formaldehyde, and a fluorinated poly(arylene ether) (FPAE) synthesized based on 4,4-(hexafluoro-isopropylidene)diphenol, decafluorobiphenyl and epoxy chloropropane. A negative fluorinated photoresist (FP) was made by composing of the FSU-8, FPAE, diphenyl iodonium salt and solvent. The refractive index and cross-linking density of the photoresists can be tuned and controlled by monitoring the feed ratio of polymers. The cross-linked material had good chemical resistance and thermal resistance. The film which was made by spinning coated the FP had good UV light lithograph sensitivity, large hardness and high glass transition temperature (Tg>170℃, after crosslinking). Low-loss optical waveguides with very smooth top surfaces were fabricated from the resulting FP by direct UV exposure and chemical development. Well-defined photolithography technique of the polymer was achieved in the presence of an appropriate photo acid generator and showed promisingness for direct photolithography technique of waveguide structures. For waveguides without upper claddings, the propagation loss of the channel waveguides was measured to be 0.21 dB/cm at 1550 nm.In chapter 4, a series of highly fluorinated polymers were synthesized by copolymerization of 2,3,4,5,6-pentafluorostyrene (PFS) and fluorinated styrene derivate monomer (FSDM). Their chemical structure were confirmed by 1H NMR, 13C NMR and 19F NMR spectra. The refractive index and cross-linking density of the polymers can be tuned and controlled by monitoring the feed ratio of comonomers. A series of negative-type low-molecular-weight fluorinated photoresists (NFPs) were prepared by composing of fluorinated polystyrene derivates (FPSDs), diphenyl iodonium salt as a photoacid generator (PAG) and solvent. The polymer films prepared from NFP by photocuring exhibited excellent chemical resistance and thermal stabilities (Td ranged from 230.5 to 258.1℃). A clear negative pattern was obtained through direct UV exposure and chemical development. For waveguides without upper cladding, the propagation loss of the channel waveguides was measured to be 0.25 dB/cm at 1550 nm.In chapter 5, a series of highly fluorinated aromatic-aliphatic polyether were synthesized by copolymerization of decafluorobiphenyl, (4-methoxy) phenylhydro-quinone and 2,2,3,3,4,4,5,5,6,6,7,7-dodeca-fluoro-1,8-octanediol. Their chemical structure were confirmed by 1H NMR,13C NMR and 19F NMR spectra. The refractive index and cross-linking density of the polymers can be tuned and controlled by monitoring the feed ratio of comonomers. A series of negative-type fluorinated aromatic-aliphatic photoresists (FA-APs) were prepared by composing of fluorinated polymers, diphenyl iodonium salt as a photoacid generator (PAG) and solvent. The polymer films prepared from FA-AP by photocuring exhibited excellent chemical resistance and thermal stabilities (Td ranged from 230 to 278℃). A clear negative pattern was obtained through direct UV exposure and chemical development. For waveguides without upper cladding, the propagation loss of the channel waveguides fabricated by FA-AP 2 was measured to be 0.19 dB/cm at 1550 nm.