High loading of nanostructured ceramics in polymer composite thick films by aerosol deposition

Low temperature fabrication of Al(2)O(3)-polyimide composite substrates was carried out by an aerosol deposition process using a mixture of Al(2)O(3 )and polyimide starting powders. The microstructures and dielectric properties of the composite thick films in relation to their Al(2)O(3 )contents were characterized by X-ray diffraction analysis. As a result, the crystallite size of α-Al(2)O(3 )calculated from Scherrer's formula was increased from 26 to 52 nm as the polyimide ratio in the starting powders increased from 4 to 12 vol.% due to the crushing of the Al(2)O(3 )powder being reduced by the shock-absorbing effect of the polyimide powder. The Al(2)O(3)-polyimide composite thick films showed a high loss tangent with a large frequency dependence when a mixed powder of 12 vol.% polyimide was used due to the nonuniform microstructure with a rough surface. The Al(2)O(3)-polyimide composite thick films showed uniform composite structures with a low loss tangent of less than 0.01 at 1 MHz and a high Al(2)O(3 )content of more than 75 vol.% when a mixed powder of 8 vol.% polyimide was used. Moreover, the Al(2)O(3)-polyimide composite thick films had extremely high Al(2)O(3 )contents of 95 vol.% and showed a dense microstructure close to that of the Al(2)O(3 )thick films when a mixed powder of 4 vol.% polyimide was used.