A comparison of threshold voltages based on the definitions
1,4,5, and 6,
i.e.,
,
(using the EKV equations),
,
and
is shown in
Figs. E.1-E.3. The data were obtained by device
simulations of a device with
,
,
and
a constant channel doping of
.
What can be seen in these figures - apart from the expected
qualitative dependencies - is that the threshold voltages differ by
some 100mV over wide ranges of parameters.
Figure E.4 shows the unique threshold current as a function of
the gate length. The deviation of this curve from a straight lineE.3
indicates a difference between definitions 2 and 6.
The reason for decrease of
at very small channel lengths is the
threshold voltage drop and the increased output conductance, which both tend
to lower the value of
determined according to definition 6.
In other words: the peak of the
is an indicator for
short-channel effects.