Porous Al2O3 thick films fabricated by aerosol deposition and low loss Al2O3–Cyanate ester hybrid films by resin infiltration

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 °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.

► Al2O3-Cyanate Ester hybrid film as an integrated substrate.
► Room-temperature deposition of nano-porous Al2O3 thick films.
► High packing density of Al2O3 particles higher than 70 vol.%.
► Low dielectric loss below 0.001 was achieved.