Modern composite materials containing carbon nanotubes for thick film technology appliance

Małgorzata Jakubowska, Dionizy Biało, Marcin Słoma, Anna Młożniak 1, 4 Politechnika Warszawska, Instytut Inżynierii Precyzyjnej i Biomedycznej, Wydział Mechatroniki, ul. św. A. Boboli 8, 02-525 Warszawa, Poland 2, 3 Instytut Technologii Materiałów Elektronicznych, ul. Wólczyńska 133, 01-919 Warszawa, Poland

Quarterly No. 2, 2008 pages 158-162

DOI:

keywords: carbon nanotubes, thick film technology, screen printed layers, conductive transparent layers

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abstract Since their first observation more than a decade ago by Iijima, carbon nanotubes (CNT) have been the focus of considerable research. Carbon nanotubes (CNTs) are allotropes of carbon. This results in a nanostructure with diameter in range of nanometers, and length from hundreds of nanometers to centimeters. Numerous investigators have reported remarkable physical and mechanical properties for this new form of carbon, very useful in many applications in nanotechnology, electronics, biology and other fields of materials science. This paper focused on thick film technology of polymer-nanotube composites. Main objective was fabrication of novel composites group of polymers filled with carbon nanotubes, for thick film technology application in microelectronics. Material used in this investigations were multiwalled carbon nanotubes characterized to be 4050 nm in diameter and 35 μm in length. Carbon material was used in “as obtained” form without purification or any further modification. From the range of organic resins two were selected for composite fabrication: PMMA-PBMA copolymer as 34% solution in butyl acetate carbide solvent, and UV curable resin NN/F-121(907)/2 as a mixture of carboxylic and ester groups polymer with Ebecryl 83 monomers and oligomers and Irgacure UV fotoiniciator. For PMMA-PBMA compositions traditional process of thick film composition fabrication was used, with minor modification. Suspension of CNT in solvent was stirred in ultrasonic bath for a half an hour, and after that resin was added and further stirred for another half an hour. After that, regular grinding in mortar was used followed by three-roll-milling process for further homogenization of CNT material in polymer resin. Similar process was used for UV curable resin composition preparation, except that nanotubes were directly added to diluted NN/F-121(907)/2 mixture. This way obtained compositions were not completely homogeneous with visible CNT agglomerates. In both cases compositions were screen printed onto glass substrate. PMMA-PBMA compositions were dried in 120C for one hour to eveporate solvent and bind polymer layer. In case of UV curable resin samples were first dried for one hour in 90C, and after that compositions were cured for 10 second by UV radiation with wavelength from 320400 nm spectrum. Stripes 30 μm thick, 1 mm wide and 25 mm long, with whole area of 25 squares were screen printed for electrical tests. Rectangles with dimensions 25x35 mm were used for light transparency measurements. To achieve more homogeneous distribution of carbon nanotubes in polymer, the whole thick film composition fabrication process was modified to suit use of such nanoscale material. Stirring of materials with particle sizes in range of nanometers is very complicated process because of the scale of particles and bonding forces between them. Therefore new stirring mechanisms were investigated including high energy sonotrode stirring and “in-situ” polymerization with NN/F-121(907)/2 resin. Unfortunately material obtained from high energy sonotrode stirring process, while characterized homogeneous in whole volume, presented higher resistance than samples prepared without sonotrode stirring. This rather unexpected result was fully understandable after SEM observations. CNT material was damaged by high energy process and cut to shorter structures, which resulted in fewer conduction paths created by nanotubes. Obtained materials with sufficient electrical and optical parameters will be used for further investigations.