tesi R. Miscioscia.pdf - EleA@UniSA

Chapter 2 61
figure 31: OTFT realized by means SAMT dielectric on ITO gate and on a Mylar substrate [37]
2.7 Source and Drain electrodes in OTFTs
Strictly thinking to the materials involved in the realization, the
performance of an organic transistor depend, and of course, not only
from the properties of the semiconductor channel and of the gate
insulator, but also from the physical-chemical properties of the source
and drain contacts that are responsible for the injection of carriers
modulated by the effect of the field within the channel region. In
particular, it is clear those technologically attractive electrodes, in
order to minimize the ohmic losses, have a high conductivity and at
the same time they are characterized by a low contact resistance (Rs)
which is often a critical factor in OFET operation (reduces the drain
current).
In addition, the interface between the electrodes and the
channel is comparable to a metal/semiconductor junction and it is
necessary to pay particular attention to the electrical characteristics of
the resulting device realized by the junction itself. The contact should
have an ohmic characteristic and this goal is achieved depends on the
barrier between the energy levels related to the contacts and the
channel.
The reduction of this barrier is obtained, for a given
semiconductor, by choosing the appropriate material with which
realize the Source and Drain, as well as by the adoption of process
improvements and interface treatments. Equally important, as regards
the feasibility of a particular transistor and its integration in complex
logic, are the possibility to realize a patterned structure of the