TDDB

Time-Dependent Dielectric Breakdown (TDDB) is a reliability failure mechanism in thin dielectric films subjected to sustained electrical stress. It is a major concern for gate oxides in metal-oxide-semiconductor (MOS) devices and for interlayer dielectrics in integrated circuits. Under high electric fields, localized defects such as traps and microvoids coalesce to form a percolating conduction path through the dielectric. Once a conductive path spans the thickness, the dielectric loses its insulating function, current rises dramatically, and a failure occurs.

TDDB lifetime, tBD, is defined as the time to breakdown under a specified constant-stress voltage, or the time at which a device crosses a defined leakage threshold; ramp tests are also used. The statistics of tBD across devices or wafers is typically described by a Weibull distribution. TDDB data are collected as functions of stress voltage, temperature, oxide thickness, and dielectric material.

Breakdown is accelerated by higher field, higher temperature, thinner dielectrics, and poorer quality (defects, impurities, interface traps). Materials include conventional SiO2 gates and advanced high-k dielectrics such as HfO2 and Al2O3; interface layers and nitridation can influence results.

To project reliability at operating conditions, empirical acceleration models relate log tBD to stress level and temperature. Common forms include field- or voltage-accelerated relations and Arrhenius-type temperature dependence. Caution is advised in extrapolations due to variability and model choice.

TDDB testing informs reliability budgets, oxide thickness selection, process optimization, and design margins. It remains a critical metric in evaluating next-generation dielectrics and scaling schemes.