### 3.5.3 Summary to: Electrical Breakdown and Failure

| The first law of materials science obtains: At field strengths larger than some critical value, dielectrics will experience (destructive) electrical breakdown |  |
|  | This might happen suddenly (then calls break-down) , with a bang and smoke, or |
|  | it may take time - months or years - then called failure. |
|  | Critical field strength may vary from < 100 kV/cm to > 10 MV / cm. |  |
| Highest field strengths in practical applications do not necessarily occur at high voltages, but e.g. in integrated circuits for very thin (a few nm) dielectric layers |  |
Example 1: TV set, 20 kV cable, thickness of insulation = 2 mm. Þ E = 100 kV/cm Example 2: Gate dielectric in transistor, 3.3 nm thick, 3.3 V operating voltage. Þ E = 10 MV/cm
|  | Properties of thin films may be quite different (better!) than bulk properties! |
| Electrical breakdown is a major source for failure of electronic products (i.e. one of the reasons why things go "kaputt" (= broke)), but there is no simple mechanism following some straight-forward theory. We have: |  |
|  | Thermal breakdown; due to small (field dependent) currents flowing through "weak" parts of the dielectric. |  |
|  | Avalanche breakdown due to occasional free electrons being accelerated in the field; eventually gaining enough energy to ionize atoms, producing more free electrons in a runaway avalanche. |  |
|  | Local discharge producing micro-plasmas in small cavities, leading to slow erosion of the material. |  |
|  | Electrolytic breakdown due to some ionic micro conduction leading to structural changes by, e.g., metal deposition. |  |
Questionaire
Multiple Choice questions to all of 3.5

© H. Föll (Advanced Materials B, part 1 - script)