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
Dielectric break down Dielectric failure
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.    
Multiple Choice questions to all of 3.5

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© H. Föll (Electronic Materials - Script)