in a conventional manner on a conventional two layer structure comprising an al 2 o 3 substrate having a metallization pattern of chromium copper chromium the borosilicate glass dielectric layer had the following composition all parts are weight parts it was formed by sedimenting the glass composition which was in the form ofa frit having a particle size of about 8 u03bc and then sintered in a hydrogen atmosphere at 820 u00b0 c for one hour the surface of the glass was then planarized in a conventional fashion to render the same flat u00b1 2 u03bc the borosilicate glass dielectric layer was then cleaned with a conventional neutral cleaning solution followed by ashing in an oxygen atmosphere in a manner conventional in the art the nitrogen deficient silicon rich si 3 n 4 layer was then plasmadeposited onto the clean surface of the borosilicate glass dielectric layer the si 3 n 4 layer had a thickness in the 4 000 to 5 000 angstrom range it had a refractive index less than 2 3 plasma deposition was conducted at about 300 u00b0 c using a power of about 300 watts and at an si 3 n 4 deposition rate of about 300 u00e5 minute after deposition of the si 3 n 4 layer the assembly was introducedinto a furnace and treated in a hydrogen atmosphere at approximately one atmosphere at 525 u00b0 c for two hours to densify the si 3 n 4 film after densification the si 3 n 4 film exhibiting a refractiveindex of about 2 5 after removal from.