7.2 Schematic Recovery Behavior

The question arises whether this different recovery shapes are due to an artifact again (cf. Chapter 6.5) or not. Therefore, the key findings are presented first. Given that aid it is possible to discuss the experimental results afterwards.

Let us assume a recovery trace that shows both features, early as well as delayed recovery. Considering the assumptions that no recovery is missed in the beginning and no additional negative charges are created at the same time till the total charges are released again yields the complete recovery trace after BTI stress, schematically depicted in the top left of Fig. 7.4. Unfortunately the full features of the recovery after typical BTI stress are rarely visible, cf. the curve of and in Fig. 7.3, as often only a part of the S-shaped recovery characteristic can be recorded by the experiment.

Figure 7.4: A schematic recovery trace after bias temperature stress is shown as solid line. Top Left: The full S-shape is only observable under certain conditions, e.g. and . For longer the whole curve is shifted to higher . PBTI mainly shows the characteristics in the top left (red) box, whereas the behavior after NBTI stress typically proceeds as shown in the bottom right (green) box. Within these sections and depend on the curvatures and mark the transition between the initial and the concluding phase of the recovery. Bottom Left: In combination with the oxide electric field dependence, the behavior of PBTI and NBTI can be obtained by scaling with and . Top Right: Increasing stress conditions ( and/or ) for PBTI yield smaller relaxation rates per decade at earlier , followed by larger relaxation rates afterwards. When extending the observation period towards larger , the transition back to smaller relaxation rates becomes visible. Bottom Right: Increased stress conditions after NBTI feature increased relaxation up to . Extending the observation period towards smaller after NBTI stress is often not possible due to the limited measurement speed.

While for PBTI only the upper section of the whole relaxation curve is visible, it is the lower section for NBTI. Within these sections the curvature marks the transition between the initial and the late phase of the recovery respectively. By using this curvature to detect a change of the relaxation the recovery following PBTI versus NBTI stress is now analyzed in more detail.