As illustrated in Fig. 7.7 the initial relaxation rate 
after NBTI stress is
higher than its PBTI counterpart. For NBTI 
increases with increasing 
,
while for PBTI 
only slightly increases with increasing 
. Due to also
higher 
at the beginning of the relaxation with higher 
, the effect
even results in lower relative recovery per decade with higher 
. Furthermore,
for PBTI 
decreases with increasing 
because of the higher contributing
permanent part.
) and second (
) logarithm are
plotted over 
as a function of the device thickness 
and its oxide
electric field 
. The slope 
of NBTI stress is higher than that resulting
from PBTI stress, and decreases with 
as shown by the solid lines. The
dashed line denotes the boundary between NBTI and PBTI. The initial
relaxation slopes 
increase from 
(PBTI) to 
(NBTI), which is
a factor of more than 
. This demonstrates the different initial relaxation
behavior following NBTI and PBTI stress.
In contrast, the long-term relaxation 
increases with 
and 
, which
clearly shows enhanced relaxation after PBTI stress, but lower relaxation after
NBTI compared to the corresponding 
, cf. Fig. 7.8. All these results support
the trends schematically shown in Fig. 7.4.
) and second (
) logarithm are
plotted over 
as a function of the device thickness 
and its oxide
electric field 
. The slope 
for the long-term characteristics increases
with 
and 
and clearly reflects the increased relaxation after PBTI
stress with values ranging from 
(NBTI) to 
(PBTI). Combining
this fact and recalling that PBTI does practically not recover during the
first few seconds supports the assumption that the performed kind of stress
condition already constitutes the short-term and long-term relaxation.
