Microstructural and dielectric characterization of sol-gel derived siliconoxycarbide glass sheets

Thin (50-1000 mu m) silicon oxycarbide glass sheets were synthesized by the pyrolysis of gel sheets obtained from a methyl-modified silica sol contain ing colloidal silica under inert atmosphere between 900 and 1450 degrees C. The microstructure of these glass sheets was investigated with the help of high resolution scanning and transmission electron microscopy (HR-SEM and HR-TEM), X-ray diffraction and Raman spectroscopy and their dielectric prop erties were determined. The surface morphology as observed with HR-SEM did not exhibit a notable temperature dependence. HR-TEM studies showed that th e glass sheets sintered up to 1200 degrees C are amorphous, whereas those s intered at 1450 degrees C contain uniformly dispersed crystallites of SiC a nd graphite. X-ray diffraction studies were found in agreement with the HR- TEM results. Raman spectroscopy showed that free carbon is present as an am orphous phase till a temperature of 1000 degrees C, whereas at temperatures greater than or equal to 1200 degrees C, the presence of graphitic carbon was observed. Silicon oxycarbide glass sheets heat treated at temperatures up to 1200 degrees C, showed a dielectric constant between 4.1 +/- 0.11 and 4.6 +/- 0.15 in the frequency range from 75 kHz to 5 MHz, with correspondi ng losses between 0.0008 and 0.1100. Such silicon oxycarbide glass sheets s intered at less than or equal to 1200 degrees C could find an application a s substrates for electronic packaging.