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enabling
innovative electronics
Here, L is the channel length, k
and C
is the capacitance of the semiconductor depletion layer.
D
Well-behaved transistor and validation of the figures of merit
For non-optimised R&D devices, it is not always straightforward to determine if the DUT is actually
an 'acceptable' transistor and to what extend the equations introduced above constitute a valid
description of the behaviour of the DUT itself. It can therefore be useful to benchmark the behaviour
of a real R&D DUT with an ideal well-behaved transistor.
The aim of this section is to give to graduate students or researchers with no previous experience of
TFT/OFET characterisation a very brief guide on data validation. Despite not being strictly rigorous,
this section should help the beginner to easily tell apart a good from a bad transistor.
In this user manual, we define a transistor as well-behaved if:
1) The IV output curves comply with the following conditions, see page Output Characteristic (I-
V)
I
is a linear function of the driving voltage for small V
DS
I
(approximately) saturates for larger V
DS
I
increase with V
DS
2) Linear and transfer characteristic curves are (approximately) described by Eqs. 1 and 6,
3) The current TC current I
17
4) The derivatives
of the gate voltage, they must always be positive with possibly no more than one peak for
V
>V
GS
T
Condition 1) guarantees that the DUT is really a field effect transistor. Discard any device that does
not comply with condition 1).
A poor carrier injection from the drain electrode to the semiconductor will results in
underperforming current I
function V
.
DS
Condition 2) is required in order for the mobility equations 4 and 8 or (9 and 10) to be valid.
Important: Failure to satisfy this condition can prevent SuperFACT from calculating the mobility.
Refer to
Mobility Errors
for a detailed description of the mobility errors code.
16
Monotonically increasing function means that for any V
(V
): large voltage always means larger drain current. For p-type transistor, where both voltage and current
GS,2
are negative, these relations hold true if the inequality symbol is reversed.
17
These derivatives, apart from a multiplicative factor, are the mobility of the transistor, see Eqs. 4 and 8.
Ossila Ltd
the Boltzmann constant, T the temperature, q the electrical charge
b
(field effect)
GS
is a monotonically
DS
(for linear TC) or
at low drain voltage, i.e. I
DS
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DS
DS
16
increasing function of V
(for saturation TC) are constant or, if functions
(V
) will increase less-than linearly as a
DS
DS
< V
, the drain current is such that I
GS,1
GS,2
GS
(V
)< I
DS
GS,1
DS
42
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