Study of tantalum oxide thin film capacitors on metallized polymer sheets for advanced packaging applications

Tantalum oxide thin film capacitors were fabricated on metallized polyimide sheet substrates and tested. It was found that the substrates' surface topography has a strong influence on the electrical properties and yields of the thin film capacitors. The leakage current density and breakdown field strength of the capacitors are qualitatively correlated to the amount and degree of surface irregularities on the substrates, which were analyzed using scanning electron microscopy (SEM), atomic force microscopy (AFM), and profilometry. It was demonstrated that Benzocyclobutene (BCB) can be used to planarize the surface irregularities and to improve the capacitor yield and performance. The importance of choosing the right substrate materials for thin film capacitor fabrication is also discussed.