tesi R. Miscioscia.pdf - EleA@UniSA

Chapter 1 25
In eq. 27, kB is the Boltzmann constant, T is the absolute temperature,
Ea is the activation energy of the process. In the hypothesis of
Arrhenius-behavior Ea can be extracted by experimentally like
suggested in [9].
The rule which is empirically obeyed for a wide variety of
thermally-activated physical processes is about the pre-factor X0 in the
eq. 27 and implies X0 growing exponentially with the activation
energy Ea like in
eq. 28
Such feature goes under the name of Meyer-Neldel Rule (MNR)
from the names of its discoverers [9].
In eq. 28 X00 is a constant (non-thermally activated) pre-factor;
EMN is the characteristic energy of the process and is named Meyer-
Neldel Energy (MNE). By substituting the MNR law (eq. 28) in the
Arrhenius law (eq. 27), we obtain:
eq. 29
This implies the existence of a typical temperature TMN=EMN/kB
(named isokinetic temperature) which makes the process X
independent from Ea and finally from the physical parameters which
make Ea change.
In the case o fan OTFT, once named X the channel’s mobility, for
T = TMN the Activation energy becomes independent from the gate
voltage. This will be by now the meaning that we attribute to the TMN.
As we told before, MNR (eq. 29) has been observed for a plethora of
physical processes but the quest for the link between the macroscopic
source of this behavior and the physical meaning of EMN is still matter
of discussion[4] because of its potentiality to be a general rule for the
determination of the break-even point in the competition of two
opposed activated processes. That’s why it has also been referred as
compensation rule.