Example Application Setup for Vth Measure-
ment
This section describes an example application setup that you should save to
the le named
VTH.MES
on diskette before executing program examples (that
use
VTH.MES
) described previously in this chapter.
A frequently used method of measuring Vth is to synchronously sweep the
exact same voltage to gate and drain, and measure the characteristics in the
saturation region.
The theoretical value of drain current in the saturation region is calculated as
follows:
Id
=
3
(
Vg
0
Vth
)
2
Where
is the gain factor, which is
0
1
=
2
3
(
ox
W=L
)
3
t
ox
. Therefore, if you
take the square root of both sides of the equation:
p
Id
=
p
3
(
Vg
0
Vth
)
p
Id
is proportional to Vg, and the slope is
p
. At the point where
p
Id
is
equal 0,
Vth
is equal to
Vg
.So, to know
Vth
, we need to nd that point.
The measurement conditions are as follows:
Channel Denition
Measurement Mode
Sweep
UNIT VNAME INAME MODE FCTN
SMU1 Vd Id V VAR1'
SMU2 Vg Ig V VAR1
SMU3 Vs Is COMMON CONST
SMU4 Vsb Isb V CONST
3-23
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