The semiconductor device reliability is defined as a degree or characteristics that indicates the functional stability of the device over a time. The degree of reliability is the probability in that the device executes its defined functions during an estimated period under defined conditions. In general, the failure rate at time 0 is expressed as part per million (ppm). The failure rate during the periods of initial and random failures is expressed as Failure in time (Fit), where 1 Fit=10-9/time. The wear-out failure period is expressed as Time To Failure (TTF), which refers to the life until a certain cumulative failure rate is reached.