Intrinsic Mechanisms of Multilayer Ceramic Capacitor Failure.
Abstract
The possible role of grain boundaries (GB) in MLC capacitors, with respect to insulation resistance and its degradation, is reviewed. Activation energy 'E sub A) can be related directly to GB barrier height, Phi sub B. The voltage dependent activation energies for poly-Si, ZnO varistors and PTC devices has been attributed directly to E sub A. Varistor and PTC device degradation is caused GB passivation. A similar voltage dependence is reported here for barrier layer and COG capacitor types where E sub A decreases from 0.91 to 0.44eV and from 1.61 to 0.90eV respectively, with concurrent super-ohmic increases in leakage current. Such a voltage dependent E sub A is not seen for X7R devices, even though the current is super-ohmic. Reasons to account for this are discussed. It is concluded that the GB potential barrier may offer a major source of impedance to leakage current for MLC capacitors, and its decrease may result in failure. It has been ascertained that E sub A decreases for degraded X7R devices, with an increase in the I-V slope. These results are consistent with our earlier reports on degraded devices, and with the space charge limited current model for emission from electrodes. X7R chips with no internal electrodes exhibit both ohmic and super-ohmic characteristics, with activation energies independent of voltage. A near-exponential rate of current increase with time, accompanied by a linear decrease in E sub A, was seen for both X7R and Z5U capacitors.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 01, 1985
- Accession Number
- ADA156638
Entities
People
- L. C. Burton
Organizations
- Virginia Tech