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Vapor Phase Growth of Functional Pentacene Films at Atmospheric Pressure

Authors

  • Cédric Rolin,

    Corresponding author
    1. imec, Polymer and Molecular Electronics Group, Kapeldreef, 75, B-3001 Leuven, Belgium
    • imec, Polymer and Molecular Electronics Group, Kapeldreef, 75, B-3001 Leuven, Belgium.
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  • Karolien Vasseur,

    1. imec, Polymer and Molecular Electronics Group, Kapeldreef, 75, B-3001 Leuven, Belgium
    2. Katholieke Universiteit Leuven, Department of Metallurgy and Materials Engineering, Kasteelpark Arenberg, 44, B-3001 Leuven, Belgium
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  • Björn Niesen,

    1. imec, Polymer and Molecular Electronics Group, Kapeldreef, 75, B-3001 Leuven, Belgium
    2. Katholieke Universiteit Leuven, Department of Electrical Engineering, Kasteelpark Arenberg, 10, B-3001 Leuven, Belgium
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  • Myriam Willegems,

    1. imec, Polymer and Molecular Electronics Group, Kapeldreef, 75, B-3001 Leuven, Belgium
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  • Robert Müller,

    1. imec, Polymer and Molecular Electronics Group, Kapeldreef, 75, B-3001 Leuven, Belgium
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  • Sören Steudel,

    1. imec, Polymer and Molecular Electronics Group, Kapeldreef, 75, B-3001 Leuven, Belgium
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  • Jan Genoe,

    1. imec, Polymer and Molecular Electronics Group, Kapeldreef, 75, B-3001 Leuven, Belgium
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  • Paul Heremans

    1. imec, Polymer and Molecular Electronics Group, Kapeldreef, 75, B-3001 Leuven, Belgium
    2. Katholieke Universiteit Leuven, Department of Electrical Engineering, Kasteelpark Arenberg, 10, B-3001 Leuven, Belgium
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Abstract

Compared to traditional vacuum evaporation techniques for small organic molecules, organic vapor phase deposition (OVPD) possesses a extra processing parameter: the pressure of process gas Pch. Here, the influence of large Pch variations (from 0.1 mbar to atmospheric pressure) on pentacene thin film growth is explored. OVPD operation at higher Pch is characterized by lower carrier gas velocities and lower organic diffusivities. These result in an invariance of the material utilization efficiency over the entire pressure span and in an advantageous equilibrium evaporation regime in the source. An increase in Pch yields rough pentacene layers. Classical nucleation theory is applied to demonstrate how the pressure rise triggers homogeneous nucleation in the gas phase, causing the observed roughening. The use of lower deposition rates, higher dilution flow rates, and higher substrate temperatures result in the suppression of gas phase nucleation and the growth of smooth pentacene films at atmospheric pressure. Using these optimized conditions, state-of-the-art pentacene thin film transistors with saturation mobilities above 0.9 cm2/Vs are reproducibly fabricated. p-Type circuits are also made and a 19-stage ring oscillator with a stage delay of 51 μs at a supply voltage of 15 V is demonstrated.

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