Regensburg 2007 – wissenschaftliches Programm
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SYOE: Symposium Organic Thin Film Electronics: From Molecular Contacts to Devices
SYOE 4: Organic Transistors
SYOE 4.2: Vortrag
Dienstag, 27. März 2007, 10:15–10:30, H1
Dielectric Interface Modification by UV irradiation: A Novel Method to control OFET charge carrier transport properties — •Niels Benson, Martin Schidleja, Christian Melzer, and Heinz von Seggern — University of Technology Darmstadt, Institute of Material Science, Petersenstr. 23, 64287 Darmstadt, Germany
In the present talk a novel concept is introduced, which allows for a change in OFET polarity by polymer dielectric interface modification. This concept is based on the irradiation of the gate dielectric by ultra violet radiation prior to the organic semiconductor deposition. As a result balanced unipolar charge carrier transport properties of n- and p-type pentacene based OFETs were obtained. The change in OFET polarity manifests itself in a large positive threshold voltage shift of approximately 60V for both charge carrier types. On the basis of detailed studies using contact angle and x-ray photo electron spectroscopy measurements, a possible cause for the threshold voltage shift is discussed. We could show that during the UV treatment step, polar groups such as C=O and according to literature -COH, recently identified as electron traps by Chua et al., are formed in the polymeric gate dielectric, influencing the OFET charge carrier properties. In line with this idea, negative charge carriers are localized within the PMMA dielectric once the UV modified OFET is driven in electron accumulation mode. This results in a positive threshold voltage shift inhibiting the electron- and promoting the hole-transport. The area density of trapped electrons necessary for the observed threshold voltage shift is estimated to be ≥3.9*1012cm−2.