The base layer effect on the d.c. conductivity and structure of direct current magnetron sputtered thin films of silver

Many low-emissivity solar-control optical coatings on glass consist of a repeating dielectric-silver-dielectric thin film period. We have investigated the effect of structure of the dielectric base layer on the conductivity, structure, and thermal stability of contiguous silver films up to 500 Angstrom thick. All individual layers were deposited by d.c.-magnetron cathode sputtering. Specifically, a detailed comparison of thin films of amorphous zinc stannate with crystalline zinc oxide showed that the latter improves the conductivity of 50-100 Angstrom and thicker silver layers. X-Ray diffraction analysis showed that zinc oxide with a preferred basal plane orientation results in the preferred growth of the Ag(111) planes parallel to the float glass substrate. Transmission electron microscopy results support the above observation. The transmission electron microscopy results also indicate that the silver-dielectric interface is of similar quality in both cases, thus eliminating the role of the interface as a major cause of the above difference. Our data on the structure and electrical properties of heat-treated samples suggest that the preferential growth of the silver layer results in its higher thermal stability. (C) 2001 PPG Industries Inc. Published by Elsevier Science B.V. All rights reserved.