Effect of alumina particle size on prevention of crystal growth in low- k silica dielectric composite

Abstract

The effect of alumina particle size on cristobalite formation in binary borosilicate glass composite, containing a low-softening Pyrex borosilicate glass and a high-softening high silica glass, has been studied. With an added alumina content greater than a critical value, however, cristobalite formation in the glass composite is completely inhibited. The critical alumina content is found to decrease with decreasing alumina particle size, from 10–15 vol.% for 3 μm to 1–2.5 vol.% for 0.02 μm at 950 °C. The above result is attributed to a strong coupling reaction between Al 3+ from alumina and Na + from Pyrex borosilicate glass. The resulting cristobalite-free glass composite has a dielectric constant of 4.5–5.5 at 1 MHz and a thermal expansion coefficient of 2.5–5.5 ppm °C −1 in the temperature range 25–200 °C.