Articles you may be interested inAmbipolar organic thin film transistors based on a soluble pentacene derivative Appl. Phys. Lett. 99, 023304 (2011); 10.1063/1.3606537Influence of polymer gate dielectrics on n -channel conduction of pentacene-based organic field-effect transistors

We demonstrate the origin and mechanism of the hysteresis behavior that is frequently observed during the operation of organic field-effect transistors (OFETs) based on polymer gate dielectrics. Although polar functionalities, such as hydroxyl groups, present in the polymer gate dielectrics are known to induce hysteresis, there have only been a few detailed investigations examining how the presence of such end functionalities both at the polymer surface—forming an interface with the semiconductor layer—and in the bulk influences the hysteresis. In this study, we control the hydrophobicity of the polymer by varying the number of hydroxyl groups, and use an ultrathin polymer/SiO2 bilayer and a thick single polymer as the gate dielectric structure so that the hysteresis behavior is divided into contributions from hydroxyl groups present at the polymer surface and in the bulk, respectively. Electrical characterizations of the OFETs, performed both in vacuum (≈10−3 Torr) and in ambient air (relative humidity of about 40%), show that the observed hysteresis is determined by the transport of water within the polymer (i.e., the adsorption at the polymer surface and the diffusion into the bulk), which in turn is controlled by the hydrophobicity and the thickness of the polymer.

Here, we report on the fabrication of low-voltage-operating pentacene-based organic field-effect transistors (OFETs) that utilize crosslinked cyanoethylated poly(vinyl alcohol) (CR-V) gate dielectrics. The crosslinked CR-V-based OFET could be operated successfully at low voltages (below 4 V), but abnormal behaviour during device operation, such as uncertainty in the field-effect mobility (μ) and hysteresis, was induced by the slow polarization of moieties embedded in the gate dielectric (e.g. polar functionalities, ionic impurities, water and solvent molecules). In an effort to improve the stability of OFET operation, we measured the dependence of μ and hysteresis on dielectric thickness, CR-V crosslinking conditions and sweep rate of the gate bias. The influence of the CR-V surface properties on μ, hysteresis, and the structural and morphological features of the pentacene layer grown on the gate dielectric was characterized and compared with the properties of pentacene grown on a polystyrene surface.

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The dependence of pentacene nanostructures on gate dielectric surfaces were investigated for flexible organic field-effect transistor (OFET) applications. Two bilayer types of polymer/aluminum oxide (Al(2)O(3)) gate dielectrics were fabricated on commercial Al foils laminated onto a polymer back plate. Some Al foils were directly used as gate electrodes, and others were smoothly polished by an electrolytic etching. These Al surfaces were then anodized and coated with poly(alpha-methyl styrene) (PAMS). For PAMS/Al(2)O(3) dielectrics onto etched Al foils, surface roughness up to approximately 1 nm could be reached, although isolated dimples with a lateral diameter of several micrometers were still present. On PAMS/Al(2)O(3) dielectrics (surface roughness >40 nm) containing mechanical grooves of Al foil, average hole mobility (mu(FET)) of 50 nm thick pentacene-FETs under the low operating voltages (|V| < 6 V) was approximately 0.15 cm(2) V(-1) s(-1). In contrast, pentacene-FETs employing the etched Al gates exhibited mu(FET) of approximately 0.39 cm(2) V(-1) s(-1), which was comparable to that of reference samples with PAMS/Al(2)O(3) dielectrics onto flat sputtered Al gates. Conducting-probe atomic force microscopy and two-dimensional X-ray diffraction of pentacene films with various thicknesses revealed different out-of-plane and in-plane crystal orderings of pentacene, depending on the surface roughness of the gate dielectrics.