Voltage Dependence of Activation Energy for Multilayer Ceramic Capacitors

Current-voltage and activation energy measurements can be used to probe grain boundary potential barriers. A common type of activation energy for Current conduction in a polycrystalline material is that due to the grain boundary potential barrier. Activation energy can be related directly to grain boundary barrier height. The height of this barrier depends on occupation of grain boundary states. Its decrease with applied voltage accounts for the superohmic current-voltage behavior of polycrystalline silicon and of ZnO varistors. It also accounts for positive temperature coefficient device behavior. A similar voltage dependence is reported here for barrier layer and COG type capacitors, where activation energies decrease from 0.99 to 0.44 eV and from 1.61 to 0.90 eV, respectively. Such decreases are not seen for X7R devices, even though currents are superohmic. Several mechanisms account for this. It is concluded that the grain boundary potential barrier may offer a major source of impedance to leakage current in multilayer ceramic capacitors, and its decrease may result in device failure.