Study on the microwave dielectric property of porous silicon nitride ceramics

This paper presents the microwave dielectric property of porous silicon nitride ceramics at a frequency of 9360 MHz, which were fabricated by the nitridation of silicon powder. The porous ceramics with different volume fractions of porosity from 18.6% to 56.2% were produced by adding different amounts of the pore-forming agent into the initial silicon powder. Microstructural analysis revealed a dense matrix containing large pores with needle-shaped and flaky β-Si₃N₄ grains distributing in it. The results showed that the dielectric constant of the ceramics decreases with increasing of the porosity. Adding α-Si₃N₄ powder in the raw silicon powder, the nitridation rate raises, and the dielectric constant and the dielectric loss of the ceramics decrease notably.