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Reducing leakage currents in n-channel organic field-effect transistors using molecular dipole monolayers on nanoscale oxides.

Authors
Type
Published Article
Journal
ACS Applied Materials & Interfaces
1944-8244
Publisher
American Chemical Society
Publication Date
Volume
5
Issue
15
Pages
7025–7032
Identifiers
DOI: 10.1021/am401278p
PMID: 23845125
Source
Medline

Abstract

Leakage currents through the gate dielectric of thin film transistors remain a roadblock to the fabrication of organic field-effect transistors (OFETs) on ultrathin dielectrics. We report the first investigation of a self-assembled monolayer (SAM) dipole as an electrostatic barrier to reduce leakage currents in n-channel OFETs fabricated on a minimal, leaky ∼10 nm SiO2 dielectric on highly doped Si. The electric field associated with 1H,1H,2H,2H-perfluoro-octyltriethoxysilane (FOTS) and octyltriethoxysilane (OTS) dipolar chains affixed to the oxide surface of n-Si gave an order of magnitude decrease in gate leakage current and subthreshold leakage and a two order-of-magnitude increase in ON/OFF ratio for a naphthalenetetracarboxylic diimide (NTCDI) transistor. Identically fabricated devices on p-Si showed similarly reduced leakage and improved performance for oxides treated with the larger dipole FOTS monolayer, while OTS devices showed poorer transfer characteristics than those on bare oxide. Comparison of OFETs on both substrates revealed that relative device performance from OTS and FOTS treatments was dictated primarily by the organosilane chain and not the underlying siloxane-substrate bond. This conclusion is supported by the similar threshold voltages (VT) extrapolated for SAM-treated devices, which display positive relative VT shifts for FOTS on either substrate but opposite VT shifts for OTS treatment on n-Si and p-Si. Our results highlight the potential of dipolar SAMs as performance-enhancing layers for marginal quality dielectrics, broadening the material spectrum for low power, ultrathin organic electronics.

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