Degradation Instabilities

Reliability of any semiconductor device is mainly determined by the physical conditions of its operation. If electrical, thermal, mechanical, or other loads are close to some limit or exceed it, then the probability of catastrophic failure is rather high. If transistor operation conditions guarantee a safe operation regime and the operating regime never exceeds SOA limits, then the failure probability is sufficiently low. However, even in this case it is never equal to zero at any real operation regime including storage. The main reason for this is continuous evolution of various degradation processes inside the transistor structure. Degradation changes in the structure are not always available to direct observation or measurements, but a direct consequence is gradual change in transistor parameters and operation capability degradation. However, some degradation relaxation processes have practically no influence on the datasheet transistor parameters until some threshold or critical value of the changes is reached. Then, attainment of the threshold results in drastic changes in transistor operation. Obviously, such processes usually do not provide the possibility of visual inspection unlike for example in the case of electromigration.