Al2O3-cyanate ester hybrid thick films were fabricated for 3-D integrated substrates by resin infiltration into Al2O3 porous thick films fabricated by an aerosol deposition (AD) process at room temperature. Although the AD process has been proposed as a low temperature process for fabricating dense ceramic thick films using submicron ceramic particles as starting powders, we carried out fabrication of porous Al2O3 thick films using nano-powders as the starting powder-employing the phenomenon that this fabricates only pressed compacts. The surface roughness and packing density of the fabricated porous Al2O3 thick films could be controlled by carrier gas flow, as a result, uniform porous Al2O3 thick films were fabricated on glass and Cu substrates at room temperature by the AD. There was no peak shift or peak broadening of x-ray diffraction patterns in the porous Al2O3 thick films compared to dense Al2O3 thick films made with submicron-starting powders. Al2O3-cyanate ester hybrid thick films were fabricated by resin infiltration into the porous Al2O3 thick films, and heated to 280 degrees C for 5 h to cure the cyanate ester. The polymerization of cyanate ester monomers was confirmed from Fourier transform infrared spectroscopy after curing. The microstructures of Al2O3-cyanate ester hybrid thick films were observed by scanning electron microscope after focused ion-beam milling. The relative permittivity and loss tangent of Al2O3-cyanate ester hybrid thick films were 6.7 at 1 MHz and 0.001, respectively. The Al2O3 content in the hybrid thick films was calculated using Hashin-Shtrikman bound theory with 3-D electrostatic simulations, and the calculated content was 72 vol.% near a face-centered cubic structure. (C) 2010 Elsevier B. V. All rights reserved.