Leakage current measurements of core/shell hyperbranched polyester/BaTiO3 composites for embedded capacitors
Résumé
Embedded passive components (into printed circuit board) can improve electrical performances (high frequency especially), reduce volume, weight and assembly cost. Moreover the reliability of embedded passives is significantly increased compared with traditional discrete component. Among dielectric materials, capacitor films based on polymer/ceramic composites are very interesting because such materials combine both low processing temperature (~200°C) of polymers and high dielectric constant of ceramics (~1000). Furthermore such hybrid composites are compatible with flexible organic substrates. However, depending on the type of composites, the value of the leakage current is variable and can be significant that is problematic for capacitor applications.
In this study, electrical properties, in particular leakage current of capacitors based on core/shell hyperbranched polyester/BaTiO3 composites are investigated. The core/shell structure allows a better dispersion of BaTiO3 particles into the polymer matrix compared with mechanical dispersion. Aggregates formation is then considerably reduced, dielectric properties are improved and the components reliability increased. Current measurements are performed using a Keithley 647 source meter in the voltage range [10 V, 40 V]. The results are compared with others obtained on structures using polyester/BaTiO3 composite (mechanical dispersion). The same BaTiO3 particles (100 nm) and the same filler content (27 wt. %) are considered for both composites.
In both cases, the values of the leakage current show a small variation depending on samples and voltage range. Comprised between 3.33 10-10A and 1.09 10-9A for the polyester/BaTiO3 composite capacitor, the leakage current is reduced between 1.61 and 3.73 (10-10A) for core/shell composite one for the same conditions mentioned above.
As a conclusion, core/shell composite materials lead to a significant decrease of leakage currents of buried capacitors and improve their electrical features.