Frequency and Temperature Dependence of Dielectric Constant of Epoxy/BaTiO3 Composite Embedded Capacitor Films (ECFs) for Organic Substrate

In this study, temperature dependence of capacitance, one of the most important properties of ECFs, was investigated. Temperature dependence of ECFs capacitance was determined by temperature dependence of dielectric constant and thickness, and among these, main factor was dielectric constant of ECFs. Dielectric constant of ECFs is determined by that of epoxy and BaTiO
₃
powders. Below 130oC, dielectric constant of ECFs increased as temperature increased, and was mainly affected by an epoxy matrix. However, above 130oC, the Curie temperature of BaTiO
₃
, the increase rate of ECFs dielectric constant started decreasing, because BaTiO
₃
powder undergoes a phase transition from a tetragonal to a cubic structure and its dielectric constant decreases at 130oC. Dielectric constant of BaTiO
₃
powder was obtained from measured dielectric constants of ECF and applying the Lichtenecker logarithmic rule. Dielectric constants of ECFs at high frequency range (0.1~10GHz) were measured using a cavity resonance method. For both powders, dielectric constants in high frequency range were about 3/4 of the dielectric constants at 1 MHz. This difference is mainly due to the decrease of dielectric constant of epoxy matrix. For BaTiO
₃
ECFs, there was a dielectric relaxation at 5~9GHz presumably due to the polarization mode change of BaTiO
₃
powder.