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|V
|<< |V
– V
DS
GS
Th
Eq. 2
Eq. 2 defines the range or region of validity of Eq. 1. In the range of validity of Eq. 1, V
compared to V
and, therefore it follows that this equation can be simplified as
GS
Eq. 3
By inverting Eq. 3, the mobility
Eq. 4
where
is the slope of the curve I
calculate the field effect linear mobility.
Since the mobility is proportional to the slope of the linear transfer characteristic curves, it follows
that these curves can be written as
Eq. 5
Figure 16. The linear mobility is proportional to the slope α of the IDS(VGS) curves, while the
threshold voltage is the intercept of these curves with the x-axis (red dot on the picture).
The field effect mobility can then be calculated by fitting the (I
straight line, the slope of which is inserted into Eq. 4 in order to obtain µ, while the intercept with
the x-axis gives the threshold voltage.
The mobility is the most important figure of merit for FET since it determines the ON/OFF speed of
the transistor, see Eq. 16.
10
Here, the extra index i is added to underline that (I
drive voltage and I
the corresponding nth measured current.
DS,I
Ossila Ltd
| and |V
| > |V
|.
GS
Th
.
can be written as
,
(V
), see Fig. 5. Eq. 6 is the equation SuperFACT uses to
DS
GS
,V
DS,i
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10
,V
) points
DS,i
DS,i
) are experimental quantities, with V
DS,i
is small
DS
.
satisfying Eq. 3 to a
the nth
DS,I
37
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