Low dielectric constant porous BN/SiCO made by pyrolysis of filled gels

BN/SiCO composite ceramics having a dielectric constant, ɛr, as low as 1.9 have been made by pyrolysis of filled gels at temperature ≥1000 °C. Such a low value of ɛr is supposed to be due to a combination of factors: the low ɛr of BN and of SiCO itself and the high amount of residual porosity present in the samples. The porous microstructure – and the related dielectric properties – obtained at 1000 °C show a very good stability up to 1400 °C. This result has been ascribed to the high viscosity of the SiCO glass and to the platelet shape particles of BN. Both factors hinder the sintering and prevent the closure of the pores.