Concerning the Physics of Failure of Barium Titanate Capacitors

During a program to develop high reliability, subminiature ceramic capacitors, it was noted that with sustained d-c voltage at elevated temperatures, dielectric breakdown occurred only in units whose previous voltage vs. current characteristics had been significantly non-ohmic. More specifically, these units showed a relationship of the form, log IE ¿ B ¿F which is similar to that for Schottky emission. Oxygen concentration cell experiments indicated that ionic charge transport contributed appreciably to conductivity for these units, but not for reliable units whose IE vs. V characteristics were ohmic. As expected for a process involving ionic motion, the degradation of the non-ohmic units was time dependent, and could be accelerated by increases in temperature and the applied field strength. A possible mechanism is proposed to account for the behavior of the unreliable units.