tesi R. Miscioscia.pdf - EleA@UniSA

Conclusions
In this PhD dissertation the role played by the gate dielectric in the
electrical performances of organic transistors is presented.
The key aspects which have been investigated about dielectrics are
the gate leakages and the models to extract the channel current, the
relationship between wettability of dielectric surfaces and the growth
of pentacene and then, the channel morphology and charge transport.
Another important factor is the optimization of the device when
keeping in mind that optimum performances are reached not just with
an OTFT having high values of charge mobility but also low threshold
voltages, low operation voltages, high saturation currents and low gate
dissipations. In order to obtain an optimized device, a process layout
and flowchart has been designed and stencils utilized to make
pattering of evaporated contacts and OSC islands.
This manufacturing method has been chosen because other
potentially more precise techniques have been evaluated and not taken
into account because they did not guarantee a working device and
good performances.
One of the caveats of analyzed OTFTs was the gate-leakage. This
non-ideal component has been studied by means of a specific circuital
model which has been developed from experimental data to explicit
the dependence between gate-to-contact currents from polarization
voltages in the OTFT.
Annealing effects have been analyzed by means of the developed
circuital model on fabricated devices in the aim to reduce, in some
cases, gate dissipations. As a result of this analysis, we found
Polyimide to be from the point of view of mobility an optimum gate
dielectric after a simple low-temperature rapid annealing. But
considering this device performances, thinking about applications
such device has to carry on, it was mandatory to obtain lower working
voltages by reducing the insulator thickness. But we found Polyimides
to be not easy to dilute and spin in continuous defect-free film
thicknesses under 1 microns. Thus, polyimide had to be abandoned in
favor of more processable materials like PMMA. In order to reduce