Dielectric breakdown decisively determines the reliability of nano-to centimeter-sized electronic devices and components. A systematic investigation of the size-dependent dielectric breakdown strength reveals a thickness-independent intrinsic regime and a thickness-dependent extrinsic regime. Besides that the breakdown strength scales with the inverse square root of the permittivity. Only recently, the intrinsic breakdown strength could be theoretically explained by density functional theory calculations, which confi rmed von Hippel's electron avalanche model. This thickness dependence resembles the difference between an intrinsic mechanical strength and a volume dependent defect size controlled Weibull mechanical strength distribution. Therefore, the hypothesis whether the thickness dependence of dielectric breakdown can be explained by a weakest link concept is discussed. Finally it is shown that the prevailing electrical conduction mechanism at the onset of dielectric breakdown is most probably dominated by space charge injection. A Griffi th type energy release rate breakdown model including space charge conductivity is presented, which allows for the explanation of the empirical results in the extrinsic regime.

The breakdown strength as well as the mechanical strength of ceramic materials decreases with increasing volume. The volume-effect of the mechanical strength can be explained by the Weibull theory. For the breakdown strength the same explanation has been often assumed.In order to validate this assumption breakdown strength and mechanical strength of alumina samples with defined porosities were compared. Differences in the Weibull moduli of breakdown and mechanical strength distributions indicate that the volume-effect cannot explain the thickness-dependence of the breakdown strength. In particular, the thicknessdependence of the breakdown strength always leads to a Weibull modulus of two which is not 2 in agreement with the measured Weibull moduli for samples with constant thickness. It can be concluded that the thickness-dependence of the breakdown strength cannot be explained by the Weibull concept. A recently developed breakdown model which is based on space charge injection is able to explain the experimental results.

No abstract

Electrical characteristics and conduction mechanisms of metal-insulator-metal capacitors with nanolaminated Al 2 O 3 -Hf O 2 dielectrics

The bulk breakdown behaviour of alumina single crystals with two different crystal orientations,   0 2 11 -plane (single crystal A) and   1 000 -plane (single crystal C), have been studied. Therefor plan-parallel single crystal samples were electrically loaded until dielectric breakdown was achieved. For each crystal orientation, a characteristic breakdown channel direction through the sample could be defined. In C-oriented crystals the breakdown channel originated parallel to the c-axis. For Aoriented crystals however, the breakdown channel crossed the sample in an oblique direction; the angle between crystal surface and breakdown channel was 60°. Here, the breakdown channel crossed the sample along an A-plane. Although the breakdown channel paths of A and C crystals are different, the observed breakdown strength are identical within the scatter range.