Tailoring dielectric properties of PDCs-SiCN with bimodal pore-structure by annealing combined with oxidation

This paper developed a novel strategy, i.e., annealing combined with oxidation to realize high ε_r′ (> 7.5) and low tanδ (< 0.2) in PDC-SiCN. The as-pyrolyzed SiCN prepared by powder consolidation was an amorphous ceramic composed of Si-C-N matrix and free carbon with a bimodal pore-structure. Dielectric properties and pore size distributions can be adjusted by annealing. Oxidation of materials featured an oxide scale on the surface and non-uniform erosion of phases in which additional loss of free carbon occurred. Dielectric properties and their response to oxidation were different under various annealing temperature. When annealing temperature reached 1500℃, sharp rise in ε_r′, ε_r′′ and tanδ with increasing temperature happened due to enhanced polarization and electrical conduction. Oxidation at 600℃lowered the ε_r′′ since depletion of free carbon broke the percolating conducting path. ε_r′ maintained at a high level because SiC and most of the heterogeneous interface contributed to ε_r′ were preserved.