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Vapor Phase Growth of Functional Pentacene Films at Atmospheric Pressure
Author(s) -
Rolin Cédric,
Vasseur Karolien,
Niesen Björn,
Willegems Myriam,
Müller Robert,
Steudel Sören,
Genoe Jan,
Heremans Paul
Publication year - 2012
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201200896
Subject(s) - pentacene , materials science , nucleation , atmospheric pressure , thin film , evaporation , saturation (graph theory) , vapor pressure , analytical chemistry (journal) , phase (matter) , chemical vapor deposition , vacuum evaporation , thin film transistor , nanotechnology , layer (electronics) , thermodynamics , organic chemistry , meteorology , chemistry , physics , mathematics , combinatorics
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 P ch . Here, the influence of large P ch variations (from 0.1 mbar to atmospheric pressure) on pentacene thin film growth is explored. OVPD operation at higher P ch 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 P ch 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 cm 2 /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.