Design, Synthesis, and Properties of Polyimides and Their Hybrid Materials for Optical Device Applications
Date Issued
2004
Date
2004
Author(s)
Yen, Cheng-Tyng
DOI
en-US
Abstract
In this dissertation, both theoretical and experimental studies were used to correlate the near-infrared optical properties with the molecular structures of polyimides. Besides, new polyimide/silica hybrid materials were developed to improve the physical properties of their parent polyimides. Low loss, low volume shrinkage photosensitive polyimide/silica hybrid materials were also synthesized for fabricating channel optical waveguides.
In the first part of this dissertation, “the chemical structure-near infrared optical property” relationship was investigated by both ab initio calculations and experiments. In Chapter 2, the substituents effects of several benzene derivatives on their C-H vibrational frequencies including fundamentals and overtones were investigated. It was found that the electron-withdrawing ability of substituents would influence the bond lengths of other C-H bonds on the aromatic ring: the stronger the electron-withdrawing ability, the shorter the adjacent C-H bond length; and the shorter C-H bonds will vibrate at higher frequencies. This characteristic can be utilized to tune the absorption position of C-H vibrational overtones in the near-infrared region. The maximum shifting of absorption positions was 30nm for the first overtones, and 15nm for the second overtones. In Chapter 3, the similar concept was extended to the polyimides. Polyimides stand for a potential candidate of materials for high performance and low cost optical waveguides. For polymers, their C-H absorption loss in the near-infrared region is critical for optical waveguide applications. In this chapter, several diamines bearing different bridge groups with different electron-withdrawing ability were used to investigate the effects of these bridge groups on the near-infrared optical properties of diamines and polyimides (synthesized with the dianhydride PMDA). It was found that the electron-withdrawing ability also could influence the C-H vibrational overtone absorption positions in the near-infrared region. Their absorption positions can be shifted up to 20nm for the first overtone, and 10nm for the second overtone. The planar waveguides of these polyimides were fabricated to investigate if the shifting of absorption band would influence their apparent optical loss. And it was found that PMDA/DPM stands for a lower optical loss at the wavelength of 1310nm than PMDA/ODA though its higher C-H number density than PMDA/ODA.
In the second part of this dissertation (Chapter 4), a new method to produce nano-sized silica particles in polyimide/silica hybrid materials was proposed. By using both inter- and intra-molecular interactions between polyimide and silica can improve their compatibility most. APrTEOS was used as the intermolecular coupling agents by covalently bonded to the ends of polyimides, and GOTMS was used as intramolecular coupling agents by the formation of hydrogen bonds between the end diols of GOTMS and carbonyl groups of polyimides. By this method, it was found that the size of silica particles can be reduced to 5nm. And their coefficients of thermal expansion can be reduced to about 2 orders in comparison with their parent polyimides.
In the third part of this dissertation (Chapter 5), a new synthesis scheme was proposed to produce photo-patternable polyimide/silica hybrid materials. By introducing the photosensitive compound of MDAE via the formation of acid/base ionic salts between tertiary amines of MDAE and carboxylic acid of poly(amic acid), the polyimide/silica hybrid materials can be patterned by direct photo-lithography acting as a negative tone photoresist. Besides MDAE, a trifunctional silane bearing a unsaturated methacrylate substituents, MPTMS, was incorporated to the silica moieties of polyimide/silica hybrid materials. In conventional ionic salt photosensitive polyimide, the volume shrinkage is considerable because all MDAE will be removed from films after the complete imidization (no more ionic salts). The incorporation of MPTMS can reduce the volume shrinkage of polyimide/silica hybrid materials to low during the curing processes, because part of MDAE was photo-crosslinked with MPTMS after the exposure step. The volume shrinkage was reduced to <10% for Polyimide/SiO2/MPTMS in comparison with >20% of that for polyimide. The prepared low shrinkage Polyimide/SiO2/MPTMS hybrid materials exhibit good lithographic resolution, excellent thermal stability, and tunable refractive indices.
Subjects
聚醯亞胺
氧化矽
感光性
混成
光波導
waveguide
polyimide
hybrid
photosensitive
silica
Type
thesis
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