Rolled Barium Titanate (Bt) Film Capacitor for Pulsed Power Application

Thin barium titanate (BT) film is being developed for use in microelectronics, electromechanical and optoelectronic applications. For this study rolled thin BaTiO₃ film capacitors were fabricated using RF sputtering techniques. Capacitor grade aluminum foil was used as the bottom electrode. The top electrode was sputtered aluminum film, which was used for quick measurement purposes. The as-deposited ceramic film on aluminum foil was very flexible at room temperature and could be easily rolled. The foil was masked to preserve side electrodes. The typical dissipation factors (DF) of these BT film capacitors were in the range of 0.002 to 0.005. A low dissipation factor is extremely important for pulsed power or high power filtering applications. These BT film capacitors had a parallel resistance of 15 to 20 mega-ohm. With the thickness of the film being 8,000 Å, the average dielectric constant was calculated to be 25. The insulation resistance was about 138 giga-ohm. The product of insulation resistance and leakage current (IR) is equal to 1014. The resistivity was calculated to be 8.1×10¹⁰ ohmcm. These film capacitors were tested at 50 volts and the correspondent leakage current was at 1×10⁻⁵ amp/cm². The breakdown strength at this stage was 4.2×10⁵ V/cm (1050 V/mil). It is expected that the partially annealing process would significantly increase the value of the dielectric constant, but may slightly increase the dissipation factor. The capacitance of BT film capacitors produced to-date had 2.1 percent dependence on frequency from 400 Hz to 100 kHz at room temperature. Thermal cycling of these samples in the temperature range of 25 to 300°C was performed. The capacitors had little temperature dependence. Rutherford Backscatter Spectroscopy (RBS) identify these samples were either titanium or oxygen enriched. Thin film x-ray diffraction and cross-sectional scanning electron microscopy (SEM) were performed to identify the structure and morphology of these capacitors. Some results of BaTiO₃ film capacitors on multilayer substrates are also presented. Measurements of dielectric and material properties are also reported concerning this study.