DIELECTRIC FILTERS MADE OF PS - ADVANCED PERFORMANCE BY OXIDATION ANDNEW LAYER STRUCTURES

For the formation of PS dielectric filters a detailed calibration of t he etch rates and refractive indices is required. The effective dielec tric function of PS was determined for different substrate doping leve ls as a function of the anodization current density by fitting reflect ance spectra. Based on these results a number of different dielectric filters were realized. For device applications a thermal oxidation ste p is necessary to reduce aging effects which occur as a result of the native oxidation of PS. In addition, thermal oxidation results in a qu alitatively improve filter performance due to a reduced absorption in the PS layers. Therefore the dielectric functions of PS oxidized in dr y O-2 at temperatures up to 950 degrees C were determined. A continuou s variation of the porosity and hence the refractive index with depth was used to realize so-called rugate filters. This type of interferenc e filter allows the design of structures with more complex reflectance or transmittance characteristics than structures consisting of discre te single layers. (C) 1997 Elsevier Science S.A.