Preparation Of Barium Strontium Titanate Thick Films By A Modified Sol-Gel Route

Abstract

Thick films of barium strontium titanate (Ba_0.6Sr_0.4TiO₃, BST) were fabricated by a modified sol-gel route. In this route, fine powders of BST ceramic in micrometer size or nanometer size were prepared by conventional ball mill or high energy ball mill respectively. The ceramic powder was uniformly dispersed into a sol precursor solution to form ceramic slurry. The chemical composition of the sol precursor was the same as the ceramic powder. The slurry prepared by the above procedure is well suspended and very stable. Thick films of BST can be prepared by either spin coating or screen printing of the slurry on to alumina substrates. Dense and crack free ceramic films in the thickness range of several micrometers to tens of micrometers can be prepared. The sintering temperature of the films is in the range of 700 °C–1200 °C, which is much lower than that of the conventional BST ceramics. Due to the low sintering temperature of the films, silver (Ag), palladium-silver (Pd-Ag) paste can be used as electrode to cofire with the films. The dielectric constant and loss tangent of the BST thick films with Ag electrode derived from spin coating and sintered at 750 °C for 2h are about 377 and 0.02 at room temperature and 100kHz, respectively, while for the films with Pd-Ag electrode derived from screen printing and sintered at 1200 °C for 2h are about 1208, and 0.016, respectively, at 0 °C and 100 kHz.

Keywords:

• MODIFIED SOL-GEL PROCESS
• THICK FILM
• SCREEN PRINTING
• TUNABLE DEVICE
• BST