Electronic Material Properties - und Geowissenschaften ...

Dielectric interface trap engineering by UV irradiation: A novel
method to control OFET charge carrier transport properties
N. Benson, M. Schidleja, C. Melzer, H. von Seggern
For modern day electronics the integration of field effect transistors with complementary
polarity on a single substrate is essential, in order to enhance the logic capability of the
respective circuits. When considering organic electronics, however, this has proven
difficult since most organic semiconductors exhibit either suitable hole (p) or electron (n)
conduction [1]. The development of organic circuitry therefore requires the deposition of
spatially separated p- and n-type organic semiconductors. However, recent publications
[2,3] revealed the importance of the dielectric/semiconductor interface for charge carrier
Drain
Ca
V DS
Pentacene
PMMA
SiO2 ++ p - Si
Gate
Fig. 1: OFET configuration of both p- and n-type
devices.
Ca
Source
transport in the OFET channel, and
demonstrated the feasibility to
determine the OFET charge carrier
transport properties by controlling the
interfacial electrical trap density.
In the current article we demonstrate
that unipolar p- and n-type OFETs can
be realized by employing pentacene
as the organic semiconductor and a
Ca source/drain metallization. The
OFETs simply differ by UV exposure of
the utilized PMMA dielectric layer in
ambient atmosphere prior to the
pentacene deposition. The OFET
substrate is a highly p-doped
1.7x1.7 cm 2 silicon waver, functioning as the gate contact, with a 200 nm thick SiO2 dry
oxide. In the following, an 120 nm thick PMMA dielectric layer was spin coated from a
2% wt THF solution. Subsequently, the PMMA layer of selected substrates was exposed
to UV light for 10 minutes in air, using
wavelengths of 254 and 185 nm with a
respective intensity of 15 mW/cm 2 and
1.5 mW/cm 2 . A 50 nm thick pentacene
layer and 100 nm thick Ca
Drain/Source contacts were then
precipitated by physical vapour
deposition, using a rate of 2 Å/s at a
chamber base pressure