Berlin 2008 – wissenschaftliches Programm

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SYSA: Symposium Tayloring Organic Interfaces: Molecular Structures and Applications

SYSA 5: Poster Session SYSA

SYSA 5.39: Poster

Dienstag, 26. Februar 2008, 14:30–20:00, Poster A

Threshold voltage shift in OFETs due to charges stored in a polymer dielectric — •Niels Benson, Christian Melzer, and Heinz von Seggern — Technische Universität Darmstadt, Institute of Materials Science, Division: Electronic Materials, Petersenstraße 23, D-64287 Darmstadt, Germany

Considering organic field effect transistors (OFETs), we recently demonstrated that a significant positive threshold voltage shift of ΔVth ≈ 60V can be obtained when negative charges are trapped in a near surface layer of a polymer gate dielectric. This charge leads to an effective field enhancement at the contacts and allows for an effective hole injection from Ca electrodes into pentacene.

Here we present the complementary experiment, were a negative ΔVth is obtained as the result of positive charges stored in the OFET dielectric. The utilized pentacene OFET comprises Au drain/source electrodes, as well as a Polymethylmethacrylat (PMMA) insulator. The positive charge is stored in the PMMA dielectric by exposing the OFET to different electric field strengths at a forming temperature of T = 108^∘C. For an electric field strength of 2MV/cm between the transistor channel and the gate electrode, during the forming step, a negative threshold voltage shift of ΔVth ≈ -29V was obtained. In addition, to the observed threshold voltage shift an electron current is measured in the pentacene OFET, comprising Au source/drain electrodes. This current occurred despite an injection barrier of ≈ 2.2eV.