Low-resistance films of polyimides with impregnated copper sulfide
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C. Nery Departamento de Fisica, Universidade Estadual de Maringa´, Av. Colombo 5790, 87020-900 Maringa´-Pr, Brazil
E. Radovanovic Instituto de Quı´mica, Unicamp, C. Postal 3154, Campinas, SP, Brazil
L.T. Taylor and N. Nazem Department of Chemistry, Virginia Tech, Blacksburg, Virginia 24061 (Received 20 February 2001; accepted 9 August 2001)
Surface modification of polyimides has been used to obtain better interaction with an inorganic material. Copper sulfide incorporation onto the surface of commercial Kapton威 polyimide showed that treatment with base was necessary for adherence of the copper sulfide to the polymeric matrix. The optimized conditions for composite preparation, obtained by response surface methodology, was pH 1.4 at 80 °C for 3.67 h. Using these conditions, we obtained electrical resistance as low as 1.0 ohm for CuS\Kapton威 composites. These optimized conditions were used to prepare other low-resistance polyimide composites. The resulting composites were analyzed by photoelectron spectroscopy. The presence of S(2p) and Cu(2p) peaks demonstrated the incorporation of copper sulfide onto the polyimide surface. Scanning electron microphotographs and the images from atomic force microscopy showed a homogeneous CuS distribution in all composites.
I. INTRODUCTION
Polyimides (PI) have found wide applications in the electronics industry as well as in areas such as sensor technology, optical fibers, gas separation membranes, and the medical field. Applications in microelectronics1 include use as an interlayer dielectric in integrated circuits, intermetal insulators in multichip modules, and thermal–mechanical passivation buffer protection layers.2,3 Kapton威, poly[N,N⬘-(oxydiphenylene)pyromellitimide], is a polyimide with high-temperature resistance, good mechanical properties, high flame resistance, good dimensional stability, and low dielectric constant.4 The properties of polyimide film can be modified by the incorporation of a variety of inorganic additives. Ideally, doped polyimide films would retain the polymer’s strength, flexibility, and thermal stability but also exhibit
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Address all correspondence to this author. J. Mater. Res., Vol. 16, No. 11, Nov 2001
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enhanced electrical conductivity and specular reflectivity. Polyimide composite films have been previously synthesized by thermal imidization of a polyamic acid solution which contained a soluble additive.5 Reliable adhesion between the metallization and the insulating polyimide layer in these films should depend on the nature of interaction between the metal and the polymer. Metal/polymer bond formation is expected to result in a strong adhesion, whereas, a purely physical interaction via van der Waals or electrostatic forces is supposed to result in weak adhesion.6 Many surface-treatment methods have been developed to increase the interfacial strength between metals and polyimide film. These include ion beam and plasma treatment methods using as starting gases water, argon, oxygen, and
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