tesi R. Miscioscia.pdf - EleA@UniSA

Gate-leakages 101
modeled with a constant voltage source. The proposed model has
allowed to estimate the channel mobility and the voltage threshold.
The mobility values of the devices estimated with the model
agrees with the SEM analysis. Further investigations will show
(chapter 3) that in the case of different topologies and dielectrics, the
variation of charge mobility with gate field will make sometimes notconsistent
the fits made with a model having a power-law dependence
of current from voltages as in the examined case.
3.7 Layout design impact of the gate-leakage
analysis
Gate leakages are often a hidden problem in many literature
reports. They become relevant when working on very thin insulating
films or leaky dielectrics like polymers or solution-processed
materials and are responsible of static dissipation in OFET-based
circuitry.
From observations of this chapter’s data analysis we can state that
the PI offers the best performances once annealed: in terms of
mobility: 0.72 cm 2 V -1 s -1 with a negligible gate leakage IG
The drawback of Polyimide utilization are the high operating voltages
(0,-100V), the it should be necessary to fabricate thinner dielectrics to
increase the insulator’s capacity Cins.
Unfortunately, we were not able to process PI layers under the
1µm thickness without obtaining gate short-circuits. But a way to
reduce active area under contacts had to be found to optimize devices
not only in terms of mobility but thresholds, gate leakages, operating
voltages and so on.
Being the overlap between S/D contacts in large part responsible
of such non-ideality effects, to improve performances we had to move
to a process/layout with patterned gates/islands. In this line of work
we can take into account three chances:
• OSC subtraction.
This is usual in inorganic devices where organics are
used just to make patterning and removed with solvents. Thus,
inorganic technology is for its nature orthogonal to patterning
technology. This method is not actable without any precaution