There are two important definitions of components failure when analysing semiconductor devices namely:-
(i) Degradation failure:- Many semiconductor devices have key parameters eg Beta (DC current gain). When measuring parameters such as this over a period of time, the component is said to have failed if the parameter values drifts outside pre-determined limits.
(ii) Catastrophic failures:- The component simply fails completely eg at end of life.
Failure mechanisms
One of the main causes of failures in GaAs and Silicon is metal migration, which is the physical flow of metal from one contact to the next due to the presence of an electric current. As metal is removed from a contact it’s surface area will reduce which increases the current density leading to eventual burn out of the contact. In addition, accumulation of metal removed from one contact, can build elsewhere causing short circuits.