Porous Al 2O 3 thick films fabricated by aerosol deposition and low loss Al 2O 3–Cyanate ester hybrid films by resin infiltration

Abstract

Al 2O 3–cyanate ester hybrid thick films were fabricated for 3-D integrated substrates by resin infiltration into Al 2O 3 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 Al 2O 3 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 Al 2O 3 thick films could be controlled by carrier gas flow, as a result, uniform porous Al 2O 3 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 Al 2O 3 thick films compared to dense Al 2O 3 thick films made with submicron-starting powders. Al 2O 3–cyanate ester hybrid thick films were fabricated by resin infiltration into the porous Al 2O 3 thick films, and heated to 280 °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 Al 2O 3–cyanate ester hybrid thick films were observed by scanning electron microscope after focused ion-beam milling. The relative permittivity and loss tangent of Al 2O 3–cyanate ester hybrid thick films were 6.7 at 1 MHz and 0.001, respectively. The Al 2O 3 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.