Insulation degradation behavior of multilayer ceramic capacitors clarified by Kelvin probe force microscopy under ultra-high vacuum

We investigated surface potential images on the cross section of degraded multilayer ceramic capacitors (MLCCs) by Kelvin probe force microscopy measured under a dc bias voltage in ultra-high vacuum. A highly accelerated lifetime test (HALT) was conducted to obtain degraded MLCCs. The high energy resolution of the present measurement allows us to observe the step-like voltage drops on dielectric layers of as-fired MLCCs. The step-like voltage drops disappear on the dielectric layers of degraded MLCCs, indicating that the resistance at grain boundaries declines with the progress of insulation degradation. Furthermore, the electric field concentrations near the electrodes are clearly observed under forward and backward bias. The discussion based on energy band diagrams suggests that the electric field concentrations near electrodes are attributable to energy barrier formed at the interface between electrode and dielectrics. In particular, the electric field concentration at cathode in HALT measured under backward bias is much higher than that at anode in HALT measured under forward bias. This implies that oxygen vacancies accumulated during HALT cause band bending near the cathode in HALT. We propose that the initial decline of resistance at grain boundaries and following electric-field concentrations at anode in HALT is essential to the insulation degradation on dielectric layers of MLCCs under dc bias voltage. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4791714]